JP4050237B2 - Image forming apparatus and image processing method used therefor - Google Patents

Description

  The present invention relates to an image processing apparatus used for forming a multi-tone image, an image forming apparatus including the image processing apparatus, and a method for determining input / output characteristics in the image forming apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer or a copying machine, when an image is output based on input multi-gradation image data, the input image In order to faithfully reproduce the data gradation, the gradation of the input image data is corrected.

  Examples of such gradation correction techniques include (1) Japanese Patent Laid-Open No. 10-173942 and (2) Japanese Patent Laid-Open No. 10-278347.

  First, in the technique (1), first, a reference patch (gradation pattern) is formed on a photoconductor, and a target density value of the reference patch is stored. On the other hand, the density value of the reference patch is directly read by an image reading unit. After reading, correction data for correcting the density gradation characteristics of the formed image is generated based on the difference between the stored target density value and the actually read density value. This makes it possible to perform highly accurate gradation correction in a short time.

  Next, in the technique (2), a test pattern in which different gradations are arranged two-dimensionally is formed on the basis of pattern information that forms a continuous gradation test pattern (gradation pattern) adjacently, Image forming conditions are controlled by reading this test pattern. As a result, the characteristics of the image forming means can be detected with high accuracy, and correction can be performed so that satisfactory image formation can be performed.

  In addition, when forming an image on a sheet of paper with the gradation pattern as a chart for the gradation correction, if an electrostatic latent image corresponding to the gradation pattern is formed on the photoconductor, A portion such as a portion where the electrostatic potential changes rapidly is generated. When such a portion is developed, the density becomes higher than the original density. This is generally referred to as an edge effect. As a technique for preventing this edge effect, for example, a technique such as (3) Japanese Patent Laid-Open No. 7-160075 is cited.

  In the technique (3), the amount of reflected light is detected from the toner adhering part and non-adhering part on the photosensitive member, the detection result is time-integrated with the order of the first order or more, and the maximum value of the integration result is detected The density of the image to be formed is controlled in accordance with the ratio between the detected maximum value of the attached portion and the maximum value of the non-attached portion. Thereby, it is possible to realize density control that is not affected by the edge effect.

  In addition, there is a technique for detecting the color of the background of the paper on which an image is formed and adjusting the density of the image to be formed based on this color in the image forming apparatus of the electrophotographic process. This makes it possible to form a good image according to the background color of the paper. Examples of such a technique include (4) Japanese Patent Laid-Open No. 2-230870 and (5) Japanese Patent Laid-Open No. 10-145598.

  First, in the technique (4), before the main scan for reading an original performed for outputting an image signal, the maximum density and the background density in a predetermined area of the original are detected and the image data is corrected. Density coefficient data and background data corresponding to the background density are calculated, and the image data is reduced based on the background data by the background removal means during the main scanning, and the density coefficient calculation means is used to reduce the density coefficient data. The corrected image data that has been subjected to the calculation for increasing the output from the background removing means is output. This makes it possible to form a clear image with good contrast regardless of the background density.

  Next, in the technique (5), a plurality of reference patches having different densities are formed, and the density and background density of each formed reference patch are measured. Then, the reference background correction amount is calculated from the measured background density measurement value and the predetermined background density target value, and the calculated reference background correction amount is not exceeded and the density of the reference patch is increased. Accordingly, either the density measurement value of each reference patch or the predetermined density target value of each reference patch is corrected by the correction amount that decreases with time. As a result, it is possible to reduce an error in image density control due to a difference in the type of paper in the highlight portion and variations in the density measuring device while avoiding excessive density correction in the high density portion.

  Further, when the gradation pattern is read by the image reading means, there is a problem that interference occurs between the spatial frequencies of the original on which the gradation pattern is formed and the CCD (image reading means), resulting in moire. Dots may occur. As a technique for preventing such interference, there is a technique described in (6) Japanese Patent Publication No. 6-95240.

  In the technique (6), when the test chart is read by the image reading unit, the optical path length of the imaging optical system of the image reading unit is changed from the optical path length at the time of reading a normal document. The spatial frequency of the means is changed to prevent interference with the spatial frequency of the image output means. Therefore, the test chart can be accurately read by the image reading means, and the characteristics can be adjusted with high accuracy. In addition, since the adjustment of the characteristic does not depend on the spatial frequency of the image output unit, the characteristic can be automatically adjusted even if various image output units having different spatial frequencies are used.

  In addition, the relationship between the density output value and the density input value is generally called a γ characteristic. In other words, this γ characteristic is a parameter representing a scale of gradation, and the gradation of the formed image is adjusted to an appropriate one by correcting the γ characteristic as appropriate. As a technique for correcting the γ characteristic, for example, the technique (1) and the technique (7) Japanese Patent No. 2643951 are cited.

  In the technique (1), as described above, the density gradation characteristic (γ characteristic) of the formed image is corrected based on the difference between the stored target density value and the actually read density value. Correction data is generated.

  In the technique (7), correction data of the image reading unit is created based on the image data of the reference chart read by the image reading unit, and corrected by the output unit based on the reference data for correcting the output unit. The read image is read by the image reading unit corrected by the generated correction data, and correction data of the output unit is generated based on the read image data.

As a result, the image reading means and the output means can be corrected separately, and the characteristic change in each means can be corrected accurately. Further, since the image reading means whose characteristics are corrected at that time is used when generating correction data of the output means, the correction of the output means can be performed with a simple configuration without using a special input device. It can be carried out.
Japanese Patent Laid-Open No. 10-173942 JP-A-10-278347 Japanese Patent Laid-Open No. 7-160075 JP-A-2-230870 Japanese Patent Laid-Open No. 10-145598 Japanese Examined Patent Publication No. 6-95240 Japanese Patent No. 2463951

  By the way, the edge effect is more greatly affected in the sub-scanning direction than in the main scanning direction of image formation. In an image forming apparatus using an electrophotographic process, when developing an electrostatic latent image corresponding to a gradation pattern, generally, the toner density of the developing apparatus is determined based on the density of a representative location, and the toner of the toner Whether or not to newly supply toner is determined based on the density. Therefore, if a high-density gradation pattern continues in the sub-scanning direction, the toner replenishment followability may be lowered.

  Therefore, if the gradation pattern is formed without taking into consideration the influence of the edge effect and the followability to replenish the electrostatic latent image of the toner, a gradation pattern having an appropriate gradation property cannot be formed. As a result, the density of the gradation pattern is not properly read by the image reading means, and the image forming apparatus is not adjusted properly.

  Here, the techniques (1) and (2) described above do not mention anything about the decrease in reading accuracy caused in the gradation pattern due to the edge effect. In the technique (3), although the density variation generated in the gradation pattern due to the edge effect is corrected, the response characteristics such as the developing bias hardly change corresponding to the edge portion of the gradation pattern. As a result, the density of the obtained gradation pattern is unlikely to be the original desired density, which causes a problem that an appropriate gradation pattern cannot be obtained.

  On the other hand, in the techniques (4) and (5) relating to the image correction based on the color of the background of the paper on which the image is formed, both of the read image data are simply converted into the background of the paper during normal image formation. It is only corrected by the data. Here, the zero level of the reading value of the image reading means is determined by reading the reference white plate, but the white degree of the paper on which the gradation pattern is formed is larger than the reading value of the reference white plate. Therefore, the background and the gradation pattern do not have an appropriate contrast for gradation correction.

  For this reason, even if the gradation pattern formed on the paper is read, the reading value of each gradation pattern does not correspond to the whiteness of the background, so the image reading means cannot obtain an appropriate reading value. Therefore, sufficient gradation correction cannot be performed. That is, the formed gradation pattern cannot be used more effectively.

  Further, in the technique (6) for preventing the interference effect generated between the spatial frequency of the original and the image reading means, the optical path length of the imaging optical system is changed in order to prevent the interference. That is, in the technique (6), it is necessary to use a mechanical means for changing the optical path length, and a separate driving means is required to improve the reading accuracy of the gradation pattern. For this reason, there is a problem that the apparatus configuration becomes complicated.

  In the techniques (1) and (7), the gradation pattern is simply read to correct the reference γ characteristic curve. Only the determination of gradation by these does not satisfy the user's preference or desire for gradation.

  The present invention has been made in view of the above-mentioned problems, and the object thereof is to make it possible to easily and appropriately determine the γ characteristic so as to satisfy a user's preference or demand for gradation. An image forming apparatus and an image processing method used therefor are provided.

  In order to solve the above-described problem, an image forming apparatus according to the present invention forms different latent patterns on a recording material by forming an electrostatic latent image on a photoconductor based on first image information. An image forming unit that forms and outputs a pattern chart, and an image processing unit that processes second image information input based on the pattern chart output from the image forming unit and adjusts image processing conditions. And an image forming apparatus capable of outputting a reading pattern chart for inputting the second image information to the image processing means by being read by an image reading means for reading an original image. The image forming means can be used by the user as a pattern chart for inputting the second image information to the image processing means. It is characterized by Flip and can output a visual pattern chart of inputting the second image information in said image processing means.

  According to the above configuration, the visual gradation pattern chart is used so as to satisfy not only the automatic gradation determination using the reading pattern chart but also the user's preference or demand for gradation characteristics. Thus, the gradation can be determined. For example, while the user visually observes the obtained visual gradation pattern chart, the hue of each color is adjusted to adjust the γ characteristic, and the density of the desired gradation pattern is changed according to the user's preference. May be. In this way, the γ characteristic can be determined easily and appropriately so as to satisfy the user's preference or demand for gradation.

  In the image forming apparatus, the image processing unit further includes a base color of the recording material on which the reading pattern chart is formed when the second image information is input using the reading pattern chart. It is preferable to adjust the image processing conditions by performing image processing on the second image information on the basis of.

  According to the above configuration, image processing is performed in consideration of the background color of the recording material forming the pattern chart at the time of shading correction. Therefore, it becomes possible to make the input density of the gradation pattern to the background more appropriate, and as a result, the gradation pattern can be read stably, so that the image forming conditions can be adjusted reliably and appropriately. Can do.

  In the image forming apparatus, the image processing unit may further reduce the amount of light applied to the reading pattern chart when the image reading unit reads the reading pattern chart, or the image reading unit It is preferable that the second image information is subjected to image processing based on the read value obtained by reducing the read gain.

  According to the above configuration, the reading value of the pattern chart (gradation pattern) by the image reading unit is read so as to be smaller than the actual value. Therefore, at the time of shading correction, even when the whiteness of the reference white plate is lower than the whiteness of the background density of the pattern chart, the background density can be read by the image reading unit. As a result, even when the whiteness of the reference white plate is lower than the whiteness of the background density, the gradation pattern is stably read by making the input density of the gradation pattern to the background more appropriate. be able to.

  In the image forming apparatus, the first image information for forming the reading pattern chart is multi-gradated by adding a dither value based on a dither matrix. Preferably, the means reads the reading pattern chart through an image filter having the same size as the dither matrix.

  According to the above configuration, since the pattern chart is read through the image filter having the same size as the dither matrix of the image information, interference occurs between the spatial frequency of the gradation pattern and the image reading means, and moire is generated. The problem of occurrence can be prevented without using mechanical means. Therefore, it is possible to easily improve the reading accuracy of the gradation pattern while avoiding the complexity of the apparatus.

  Further, in the image forming apparatus, the image forming unit further includes a high density in the reading pattern chart based on both the input accuracy of the image reading unit and the image forming accuracy of the density in the image forming unit. It is preferable to form the reading pattern chart so that the output value of the image reading unit in the gradation pattern on the side is larger than the output value of the image reading unit in the gradation pattern on the low density side.

  According to the above configuration, since the image is formed based on both the image forming accuracy in the density of the image forming unit and the input accuracy of the density of the image reading unit, variations occurring in the image forming accuracy and the input accuracy are caused. A pattern chart can be formed in consideration. As a result, it is possible to avoid the occurrence of a reversal phenomenon that is likely to occur in the pattern chart, and the gradation pattern that is originally on the higher density side becomes a value corresponding to the lower density side, thereby preventing unnecessary formation of the pattern chart. Thus, more accurate image forming conditions can be adjusted.

  Further, in the image forming apparatus, the first image information for forming the reading pattern chart is multi-gradated by adding a dither value based on a dither matrix. The means reads the relationship between the target reading value of the reading density of the image reading means and the reading reference value of the image reading means determined corresponding to the target reading value, and the reading pattern chart as the image reading means. It is preferable to perform image processing for obtaining the relationship between the input density of the image forming means and the dither value based on the relationship between the actual read value obtained by reading the image and the dither value.

  According to the above configuration, the relationship between the input density obtained based on the reading reference value and the actual reading value and the dither value at the time of image formation is determined as appropriate. Therefore, even if the relationship of the reference γ characteristic is not stored in the storage means, it is only necessary to have a correspondence table between the target input value of the concentration of the γ characteristic and the input reference value, which requires only a small memory capacity. The optimum γ characteristic can always be easily obtained.

  Further, in order to solve the above problems, the image processing method according to the present invention forms a pattern chart in which different gradation patterns are arranged on a recording material based on image information, and image formation is performed using this pattern chart. In an image processing method for adjusting image forming conditions of an apparatus, a step of outputting a reading pattern chart for adjusting image forming conditions by being read by an image reading means for reading a document image, and a user use And a step of outputting a visual pattern chart for adjusting the image forming conditions according to the user's request.

  According to the above configuration, the visual gradation pattern chart is used so as to satisfy not only the automatic gradation determination using the reading pattern chart but also the user's preference or demand for gradation characteristics. Thus, the gradation can be determined. For example, while the user visually observes the obtained visual gradation pattern chart, the hue of each color is adjusted to adjust the γ characteristic, and the density of the desired gradation pattern is changed according to the user's preference. May be. In this way, the γ characteristic can be determined easily and appropriately so as to satisfy the user's preference or demand for gradation.

  The image processing method further includes a first step of forming a plurality of types of gradation patterns corresponding to different known dither values on the recording material by the image forming means as the reading pattern chart, and image reading. The reading pattern chart is directly read and input by the means, and the second step of storing the relationship between the input value and the dither value is determined corresponding to the target value of the input density of the image reading means. It is preferable to have a third step for obtaining the relationship between the input density of the image forming means and the dither value based on the read reference value and the read value stored in the second step.

  According to the above method, the relationship between the input density obtained based on the reading reference value and the actual reading value and the dither value at the time of image formation is determined as appropriate. Therefore, even if the relationship of the reference γ characteristic is not stored in the storage means, it is only necessary to have a correspondence table between the target input value of the concentration of the γ characteristic and the input reference value, which requires only a small memory capacity. The optimum γ characteristic can always be easily obtained.

  In the image processing method, the fourth step of forming the visual pattern chart on the recording material based on the relationship between the input density and the dither value determined in the third step, and the visual inspection And a value corresponding to the target value obtained from the relationship adjusted in the fifth step by manually adjusting the relationship by visually observing the pattern chart, is used as the reading reference value. 6 strokes are preferred.

  According to the above method, not only the reading pattern chart but also the density of the visual pattern chart determined by the user's visual observation can be added to the image processing. Therefore, the γ characteristic can be determined easily and appropriately.

  In the processing method, any one of the reading reference value obtained in the sixth step and the reading reference value determined corresponding to the target input value of the input density in the third step is further provided. Is preferably used as the reading reference value for the third stroke.

  According to the above method, there are two types of standard reading reference values (values determined in the third step) and reading reference values taking into account user preferences (values obtained in the sixth step). The reading reference value is properly used. Therefore, for example, when the image forming apparatus is shipped from the factory, it is not necessary to consider the user's preference. Therefore, the standard reading reference value is used, and the apparatus is installed at the user's hand. In this case, set the reading reference value taking into account the user's preference. Furthermore, when the user moves the device, the original standard reading reference value is used. The reading reference value can be made appropriate depending on the situation. As a result, the setting can be simplified.

  In the image processing method, it is preferable that the number of gradations of the reading pattern chart is larger than the number of gradations of the visual pattern chart.

  In general, when the gradation is determined by the image reading unit, it is possible to determine the gradation more accurately when the number of gradations is larger. However, when the user visually determines the gradation, If the number of gradations is too large, the determination becomes complicated and accurate gradation determination cannot be performed. On the contrary, if the number of gradations is small, it is suitable for the user's determination, but the image reading means cannot make an accurate determination. On the other hand, according to the above method, the number of gradations of the reading pattern chart (first image) is larger than the number of gradations of the visual pattern chart (second image). Can be determined.

  That is, according to the above method, the number of gradations of the reading pattern chart (first image) is larger than the number of gradations of the visual pattern chart (second image). When the user visually adjusts the image forming conditions, the gradation is increased or the adjacent gradation is difficult to visually distinguish. It can be avoided.

  An image forming apparatus according to the present invention forms and outputs a pattern chart in which different gradation patterns are arranged on a recording material by forming an electrostatic latent image on a photoconductor based on first image information. Forming means and image processing means for processing second image information input based on the pattern chart output from the image forming means and adjusting image processing conditions, and the image forming means includes a document In an image forming apparatus capable of outputting a reading pattern chart for inputting the second image information to the image processing means by being read by an image reading means for reading an image, the image forming means includes image processing As a pattern chart for inputting the second image information to the means, the user uses the second image information according to the request of the user. An output possible is configured a visual pattern chart is input to the image processing means.

  According to the above configuration, the visual gradation pattern chart is used so as to satisfy not only the automatic gradation determination using the reading pattern chart but also the user's preference or demand for gradation characteristics. As a result, it is possible to determine the gradation, and it is possible to easily and appropriately determine the γ characteristic.

An embodiment of the present invention will be described with reference to FIGS. 1 to 40 as follows. Note that the present invention is not limited to this.
The image forming apparatus according to the present invention is adjacent to the gradation pattern in the sub-scanning direction of the image forming unit when generating a gradation pattern in which different gradations are arranged by the image forming unit for gradation correction. The density difference between the regions is set within a predetermined value where the density of the gradation pattern is not affected by the edge effect.

  In addition, the image forming apparatus according to the present invention expands the dynamic range by correcting the background of the gradation pattern, and the size of the image filter at the time of gradation pattern reading is the same size as the dither matrix of the gradation pattern. This makes it possible to appropriately adjust the image forming conditions of the image forming apparatus by making the reading density of the gradation pattern more appropriate.

  Furthermore, an image forming apparatus and an image processing method used for the image forming apparatus according to the present invention include a read value obtained by reading a gradation pattern corresponding to a known dither value by an image reading unit (image information input unit), and target image formation. By determining the relationship between the output density of the image forming means and the dither value in the multi-value dither method based on the reference reading value of the image reading means determined corresponding to the density, the γ characteristic is easily and appropriately determined. Make it possible to do.

  First, the configuration of the image forming apparatus according to the present invention will be described. As shown in FIG. 2, the image forming apparatus according to the present invention has a color image reading unit (image reading means, hereinafter simply referred to as an image reading unit) 110 disposed above and a color image forming unit (hereinafter referred to as “image reading unit”). 2 is a digital color copying machine (hereinafter simply referred to as image forming apparatus 1) provided with an image processing unit 2 (not shown) (not shown).

  In the main body of the image forming apparatus 1, a document table 111, a double-sided document automatic feeder (RADF: Reversing Automatic Document Feeder) 112, and an operation panel 5 described later are provided above the image reading unit 110. .

  The document table 111 is disposed on the upper surface of the main body of the image forming apparatus 1. On the other hand, the RADF 112 is supported on the upper surface of the document table 111 so as to be openable and closable with respect to the document table 111, and is mounted on the surface of the document table 111 with a predetermined positional relationship. The RADF 112 performs a double-sided conveyance operation for automatically placing both sides of a document on the document table 111.

  The duplex conveyance operation will be described. First, the document is conveyed toward the document table 111 such that one side of the document is opposed to the image reading unit 110 at a predetermined position on the document table 111. Next, after the image input by the image reading unit 110 (image reading) is finished on this one side, the original is placed on the original so that the other side faces the image reading unit 110 at a predetermined position on the platen 111. Transport toward the table 111. When the image input on both sides of one original is completed by the above operation, the RADF 112 discharges the original to the paper output unit provided in the RADF 112 and executes the same double-sided conveyance operation for the next original. To do. Note that the operations of conveying the document and turning the front and back by the RADF 112 are controlled in relation to the operation of the entire image forming apparatus 1.

  The image reading unit 110 is disposed below the document table 111 in order to input image information of the document conveyed on the document table 111 by the RADF 112, and reciprocates in parallel along the lower surface of the document table 111. It has first and second document scanning bodies 113 and 114 that move, an optical lens 115, a CCD (Charge Coupled Device) 116 that is a photoelectric conversion element, and the like.

  The first document scanning body 113 has an exposure lamp that exposes the surface of the document image and a first mirror that changes the reflected light image from the document in a predetermined direction. And reciprocating in parallel at a predetermined scanning speed while maintaining a certain distance. The second document scanning unit 114 has second and third mirrors that further deflect the reflected light image from the document deflected by the first mirror of the first document scanning unit 113 in a predetermined direction. The first document scanning body 113 reciprocally moves in parallel while maintaining a constant speed relationship.

  The optical lens 115 reduces the reflected light from the original deflected by the third mirror of the second original scanning body 114 and forms the reduced optical image at a predetermined position on the CCD 116. The CCD 116 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal.

  The CCD 116 reads a black and white image or a color image on the surface of a document, and can output line data that is color-separated into R (red), G (green), and B (blue) color components. It is a color CCD line sensor. The document image information converted into an electrical signal (RGB signal or the like) by the CCD 116 is further transferred to the image processing unit 2 described later, and image processing such as the color correction processing described above is performed.

  The image forming unit 210 disposed below the image reading unit 110 is located at substantially the center of the image forming apparatus 1, and includes a paper tray 251, a paper feed mechanism 211, a pair of registration rollers 212, image forming stations Pa to Pd, A transfer conveyance belt mechanism 213, a fixing device 217, a switching gate 218, a discharge roller 219, a discharge tray 220, a switchback conveyance path 221 and the like are provided.

  The paper tray 251 is disposed below the image forming unit 210 and stores paper P that is a recording medium. Similarly to the paper tray 251, the paper feed mechanism 211 is disposed below the image forming unit 210, and separates the sheets P stacked and accommodated in the paper tray 251 one by one to form the image forming stations Pa˜ of the image forming unit 210. Supply toward Pd. The pair of registration rollers 212 is configured such that two rollers are opposed to each other through a conveyance path of the paper P at a position before the paper P is conveyed in the image forming stations Pa to Pd. The registration roller 212 controls the timing when the fed paper P is conveyed to the image forming stations Pa to Pd. Note that the sheet P on which an image is formed on one side is re-supplied to the image forming stations Pa to Pd in accordance with the image forming timing of the image forming stations Pa to Pd.

  The image forming stations Pa to Pd form an image on the conveyed paper P. The transfer / conveying belt mechanism 213 is disposed below the image forming stations Pa to Pd, and the sheet P is placed on the transfer / conveying belt 216 stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel. Transport by electrostatic adsorption. Details of the transfer / conveyance belt mechanism 213 will be described later.

  The fixing device 217 is disposed on the downstream side of the transfer conveyance belt mechanism 213 (that is, on the downstream side in the paper conveyance direction), and fixes the toner image transferred and formed on the paper P onto the paper P. The fixing device 217 is provided with a pair of fixing rollers, and the sheet P that has passed through the nip between the fixing rollers is attached to the outer wall of the image forming apparatus 1 by a discharge roller 219 through a conveyance direction switching gate 218. The paper is discharged onto the paper discharge tray 220.

  The switching gate 218 selectively selects a conveyance path of the fixed sheet P between a path for discharging the sheet P to the image forming apparatus 1 and a path for resupplying the sheet P toward the image forming unit 210. It is designed to switch. The paper P whose transport direction has been switched again by the switching gate 218 toward the image forming stations Pa to Pd is turned upside down via the switchback transport path 221 and then supplied again to the image forming stations Pa to Pd. The

  As described above, four image forming stations Pa to Pd are provided adjacent to the transfer conveyance belt 216 above the transfer conveyance belt mechanism 213. These image forming stations Pa to Pd are arranged in the order of the image forming stations Pa, Pb, Pc, and Pd from the upstream side when viewed from the conveyance direction of the paper P, and form images with toners of different colors. .

  Note that the first image forming station Pa, the second image forming station Pb, the third image forming station Pc, and the fourth image forming station Pd are arranged from the upstream side in the conveyance direction of the paper P. In the present embodiment, the first image forming station Pa forms an image with black (black / K) toner, the second image forming station Pb forms an image with cyan (C) toner, The third image forming station Pc forms an image with magenta (M) toner, and the fourth image forming station Pd forms an image with yellow (Y) toner.

  The transfer / conveying belt mechanism 213 includes a transfer / conveying belt 216, a driving roller 214, a driven roller 215, a sheet adsorption charger 228, and a static eliminator 229. As described above, the transfer belt mechanism 213 is arranged below the image forming stations Pa to Pd, and the transfer conveyance belt 216 is stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel. ing. A portion where the transfer conveyance belt mechanism 213 is arranged becomes a sheet conveyance path.

  The transfer / conveying belt 216 is supported substantially in parallel by a driving roller 214 and a driven roller 215, and is driven to rotate by the driving roller 214. As the direction of this rotational drive, as shown in FIG. 2, the side of the transfer conveyance belt 216 facing the image forming stations Pa to Pd is driven so as to move from the registration roller 212 side to the fixing device 217 side (FIG. Middle arrow Z). At this time, as described above, the paper P supplied from the paper feeding mechanism 211 is carried, and the paper P is sequentially conveyed to the image forming stations Pa to Pd.

  The surface of the transfer conveyance belt 216 is charged by a sheet adsorption charger 228 in order to stably convey the sheet P. The sheet adsorbing charger 228 is provided between the first image forming station Pa and the sheet feeding mechanism 211, that is, on the upstream side in the rotation direction of the transfer conveyance belt 216. As a result, the paper P supplied from the paper feed mechanism 211 is transported without shifting between the first image forming station Pa and the fourth image forming station Pd in a state where the paper P is reliably adsorbed on the transfer transport belt 216. Is done.

  On the other hand, a static eliminator 229 is provided on the downstream side in the rotation direction of the transfer conveyance belt 216, that is, almost directly above the drive roller 214 between the fourth image forming station Pd and the fixing device 217. An AC voltage is applied to the static eliminator 229 in order to separate the sheet P electrostatically attracted to the transfer conveyance belt 216 from the transfer conveyance belt 216. As a result, the paper P is peeled off from the transfer conveyance belt 216.

  Each of the image forming stations Pa to Pd has substantially the same configuration. Each of the image forming stations Pa, Pb, Pc, and Pd is disposed to face the transfer conveyance belt 216, and is rotationally driven in the rotation direction and forward direction of the transfer conveyance belt 216 (in the direction of arrow F in FIG. 2). Photosensitive drums 222a, 222b, 222c and 222d are included.

  Around the photosensitive drums 222a to 222d, there are chargers 223a, 223b, 223c, and 223d, developing devices 224a, 224b, 224c, and 224d, transfer devices 225a, 225b, 225c, and 225d, and cleaning devices 226a, 226b, 226c, and 225d. 226d is arranged in this order along the rotation direction of the photosensitive drums 222a to 222d.

  The chargers 223a, 223b, 223c, and 223d uniformly charge the photosensitive drums 222a to 222d, respectively. The developing devices 224a, 224b, 224c, and 224d develop the electrostatic latent images formed by laser beam scanner units 227a, 227b, 227c, and 227d, which will be described later, on the photosensitive drums 222a to 222d, respectively. The transfer units 225a, 225b, 225c, and 225d transfer the developed toner images on the photosensitive drums 222a to 222d onto the paper P. The cleaning devices 226a, 226b, 226c, and 226d remove toner remaining on the photosensitive drums 222a to 222d.

  Laser beam scanner units (hereinafter abbreviated as LSU) 227a, 227b, 227c, and 227d are provided above the photosensitive drums 222a to 222d, respectively. The LSUs 227a to 227d include semiconductor laser elements (not shown), polygon mirrors (deflecting devices) 240a to 240d, fθ (scanning) lenses 241a to 241d, mirrors 242a, 242b, 242c, and 242d and 243a, 243b, 243c, and 243d. It has. The semiconductor laser element emits light modulated according to output data on which image processing such as color correction has been performed by the image processing unit 2 described above. The polygon mirrors 240a to 240d deflect the laser beam from the semiconductor laser element in the main scanning direction. The fθ lenses 241a to 241d, the mirrors 242a to 242d and 243a to 243d, etc., image the laser beams deflected by the polygon mirrors 240a to 240d on the surfaces of the photosensitive drums 222a to 222d.

  An image signal corresponding to a black component image in a color original image is input to LSU 227a, an image signal corresponding to an image of a cyan component in a color original image is input to LSU 227a, and magenta in the color original image is input to LSU 227c. An image signal corresponding to the component image is input, and an image signal corresponding to the yellow component image in the color original image is input to the LSU 227d.

  The developing devices 224a to 224d provided in the image forming stations Pa to Pd respectively store toners of colors corresponding to the image signals input to the image forming stations Pa to Pd. Specifically, the developing device 224a contains black toner, the developing device 224b contains cyan toner, the developing device 224c contains magenta toner, and the developing device 224d contains yellow toner. The electrostatic latent images on the photosensitive drums 222a to 222d are developed with the toners of these colors. As a result, the document image information is reproduced as a toner image of each color by the image forming unit 210.

  In the image forming apparatus 1 having the above configuration, cut sheet-like paper is used as the paper P. When the paper P is sent out from the paper tray 251 and supplied into the paper feed path guide in the paper feed mechanism 211, the leading end of the paper P is detected by a sensor (not shown). Based on the detection signal output from the sensor, it is temporarily stopped by the pair of registration rollers 212.

  Then, the paper P is sent onto the transfer conveyance belt 216 rotating in the direction of the arrow Z in time with each of the image forming stations Pa to Pd. At this time, since the transfer conveyance belt 216 is charged by the sheet adsorbing charger 228 as described above, the sheet P is stably conveyed and supplied while passing through the image forming stations Pa to Pd. Is done.

  In each of the image forming stations Pa to Pd, black, cyan, magenta, and yellow toner images are formed and superimposed on the support surface of the paper P that is electrostatically attracted and conveyed by the transfer conveyance belt 216. When the transfer of the image by the fourth image forming station Pd is completed, the sheet P is sequentially peeled off from the transfer conveyance belt 216 by the charge eliminator 229 from the leading end portion thereof and guided to the fixing device 217. Finally, the paper P on which the toner image is fixed is discharged onto a paper discharge tray 220 from a paper discharge port (not shown).

  In the above description, the LSUs 227a to 227d perform optical writing on the photosensitive drums 222a to 222d by scanning and exposing a laser beam. However, writing means for performing optical writing on the photosensitive drums 222a to 222d is not limited to the LSUs 227a to 227d.

  For example, as another writing means, a writing optical system (LED: Light Emitting Diode head) including a light emitting diode array and an imaging lens array may be used. The LED head is smaller in size than the laser beam scanner unit, has no moving parts, and is silent. Therefore, it can be suitably used in a tandem digital color image forming apparatus that requires a plurality of optical writing units.

  The image processing unit 2 provided in the image forming apparatus 1 will be described. As shown in FIG. 3, the image processing unit 2 includes an image data input unit 40, an image data processing unit 41, an image memory 43 including a hard disk device or a RAM (random access memory), an image data output unit 42, A central processing unit (hereinafter abbreviated as CPU) 44, an image editing unit 45, external interface units 46 and 47, and an image determination unit 48 are configured.

  The image data input unit 40 includes a color CCD 40a, a shading correction circuit 40b, a line matching unit 40c, a sensor color correction unit 40d, an MTF correction unit 40e, a γ correction unit 40f, and the like.

  As described above, the color CCD 40a is a three-line color CCD that can read a monochrome document or a color document image and output line data that is color-separated into RGB color components. The image reading unit 110 shown in FIG. This corresponds to the CCD 116 which is a photoelectric conversion element.

  The shading correction circuit 40b corrects the line image level of the line data read by the color CCD 40a. The line alignment unit 40c corrects the deviation of the image line data read by the color CCD 40a, and includes a line buffer and the like.

  The sensor color correction unit 40d corrects the color data of the line data of each color output from the three-line color CCD 40a. The MTF correction unit 40e corrects the change in the signal of each pixel so as to have an edge. The γ correction unit 40f corrects the brightness of the image and corrects the visibility.

  The image data processing unit 41 includes a monochrome data generation unit 41a, an input processing unit 41b, a region separation unit 41c, a black generation unit 41d, a color correction circuit 41e, a zoom processing circuit 41f, a spatial filter 41g, a halftone processing unit 41h, and the like. I have.

  The monochrome data generation unit 41a generates monochrome data from RGB signals that are color image signals input from the image data input unit 40 when the document is a monochrome document.

  When the document is a color document, the input processing unit 41b converts the R, G, and B signals that are color image signals input from the image data input unit 40 into CMY signals corresponding to the image forming stations Pb, Pc, and Pd. In addition, a clock conversion process and an AE histogram process are also performed. By the AE histogram process, character information and picture information in the document can be separated from the color image signal input from the image data input unit 40.

  The area separation unit 41c separates whether the image data input from the monochrome data generation unit 41a or the input processing unit 41b is a character part, a halftone dot photograph, or a photographic paper photograph.

  The black generation unit 41d generates black by performing undercolor removal processing based on the CMY signal output from the input processing unit 41a, and generates black color data (K signal) when forming a color image. is there. The color correction circuit 41e adjusts each color of each CMY color image signal based on each color conversion table.

  The zoom processing circuit 41f converts the input image information based on the set magnification. The halftone processing unit 41h is for expressing gradation such as multilevel error diffusion and multilevel dither.

  The image memory 43 temporarily stores the image data of each color that has been subjected to the halftone processing by the halftone processing unit 41h. The image memory 43 is an 8-bit four-color (32-bit) serial output from the image data processing unit 41. Four hard disks (rotating storage media) 43a, 43b, and 43c that sequentially receive image data, convert them from 32-bit data to 8-bit 4-color image data and store them as image data for each color while temporarily storing them in a buffer -It has 43d.

  Further, since the image memory 43 has different positions of the image forming stations Pa, Pb, Pc, and Pd, each color image data is temporarily stored in the delay buffer memory 43e (semiconductor memory) of the image memory 43, and the time is shifted. Thus, the timing for sending image data to each of the LSUs 227a to 227d is matched to prevent color misregistration. The image memory 43 further includes an image synthesis memory (not shown) for synthesizing a plurality of images.

  The image data output unit 42 includes a laser control unit (hereinafter abbreviated as LCU) 42a and LSUs 42b, 42c, 42d, and 42e.

  The LCU 42a performs pulse width modulation based on the image data of each color from the halftone processing unit 41h. The LSUs 42b, 42c, 42d, and 42e perform laser recording based on a pulse width modulation signal corresponding to the image signal of each color output from the LCU 42a. These LSUs 42b to 42e correspond to the LSUs 227a to 227d in the image forming unit 210 shown in FIG.

  The CPU 44 controls the image data input unit 40, the image data processing unit 41, the image memory 43, the image data output unit 42, the image editing unit 45, which will be described later, and the external interface units 46 and 47 based on a predetermined sequence. It is.

  The image editing unit 45 temporarily performs predetermined image editing on the image data stored in the image memory 43 via the image data input unit 40, the image data processing unit 41, or external interfaces 46 and 47 described later. belongs to. This image data editing operation is performed using an image composition memory in the image memory 43.

  The external interface 46 is an external image input processing means provided separately from the image forming apparatus 1, for example, a communication interface means for receiving image data from a communication portable terminal, a digital camera, a digital video camera, etc. Image information input means).

  It is preferable that the image data input from the external interface 46 is also temporarily input to the image data processing unit 41 to perform color space correction or the like. As a result, the data is converted to a data level that can be handled by the image recording unit 210 of the image forming apparatus 1 and then stored and managed in the hard disks 43 a to 43 d of the image memory 43.

  Further, the external interface 47 is a printer interface for inputting image data created by a personal computer (not shown), and is a monochrome or color FAX interface for receiving image data received by FAX. The image data input from the external interface 47 is already a CMYK signal, and is subjected to halftone processing by the halftone processing unit 41h and stored and managed in the hard disks 43a to 43d of the image memory 43.

  The image determination unit 48 separates a character area and a photographic area for area separation, and determines whether the reading area is a color image or a monochrome image. Furthermore, it is also used for collating various patterns included in the read image to prevent copying of banknotes and securities. Note that pre-scanning is necessary when determining whether the reading area is a color image or a monochrome image.

  The control system for controlling the operation of the entire apparatus in the image forming apparatus 1 will be described. As shown in FIG. 4, the operation of each part of the entire apparatus is managed by the CPU 44.

  Details of the image data input unit 40, the image data processing unit 41, the image data output unit 42, the image memory 43, the CPU 44, and the external interface 46 shown in FIG. 4 are as described above. The density sensor 140 is for measuring the density of high-density toner patches formed on the surfaces of the photosensitive drums 222a to 222d, as will be described later. The external interface 46 can exchange data with the image memory 43 and is further connected to the CPU 44 via the image memory 43.

  In addition, the CPU 44 manages each drive mechanism unit constituting the image forming apparatus 1 such as the RADF 112, the image reading unit 110, and the image forming unit 210 by sequence control, and outputs a control signal to each unit.

  Further, an operation board unit 48 including an operation panel 5 is connected to the CPU 44 so as to be able to communicate with each other, and a control signal indicating the copy mode contents set and inputted by the operator according to the operation of the operation panel 5 is sent to the CPU 44. The entire image forming apparatus 1 is controlled to operate according to the set mode.

  Further, control signals indicating various operation states of the image forming apparatus 1 including an operation panel 5 (see FIG. 5) to be described later are connected from the CPU 44 so as to be able to communicate with the operation board unit 49.

  When the user sets a copy mode (copy mode) using the operation panel 5, a control signal indicating the content is transferred from the operation board unit 49 to the CPU 44, whereby the CPU 44 controls the entire image forming apparatus 1. Control to operate according to the set mode.

  On the other hand, control signals indicating various operation states of the image forming apparatus 1 are transferred from the CPU 44 to the operation board unit 49. On the operation board unit 49 side, what kind of image forming apparatus 1 is currently in response to this control signal. Whether it is in a state or not is displayed on a touch panel type liquid crystal display device 6 of color display (described later) provided on the operation panel 5 so that the user can recognize it.

  Next, the operation panel 5 will be described. As shown in FIG. 5, the operation panel 5 is provided with a color display touch panel type liquid crystal display device 6 (hereinafter referred to as a color LCD) at the center. On the right side, a numeric keypad 8, a start key 11, a clear key 9, and an all release key 10 are arranged. A dial 7 for adjusting the brightness of the screen of the color LCD 6 is disposed on the left side of the color LCD 6.

  Of the key group arranged on the right side of the color LCD 6, the numeric keypad 8 is a key used for inputting numerical values on the screen of the color LCD 6, and the start key 11 is a key for instructing the start of the image forming operation. . The mode switching key 12 is a key for selecting an image forming operation from any one of a copy mode, a FAX mode, and a print mode.

  The clear key 9 is a key for clearing a set value displayed on the color LCD 6 or interrupting the image forming operation, and the all cancel key 10 is a key for returning the image forming condition setting to the default value. . Although not shown in FIG. 5, the operation panel 5 may be provided with an interrupt key which is a key for temporarily interrupting the image forming operation being executed and allowing other copying.

  Various screens are switched and displayed on the screen of the color LCD 6 as described later. In these screens, touch keys for setting various conditions are arranged, and various conditions can be set by directly pressing the touch keys with a finger (hereinafter simply referred to as operation). Yes. Further, operation guidance and warnings are also displayed on the color LCD 6.

  The outline of the screen displayed on the color LCD 6 will be described below. If the image forming apparatus 1 is in a standby state, the color LCD 6 displays a standby screen 601 as shown in FIG. On the upper side of the standby screen 601, there are a message area 602 and an image formation number display area 603. In the message area 602, a message for instructing an operation procedure is appropriately displayed so that the user can operate the operation panel 5 with certainty. In the image forming number display area 603, the number of images to be formed is input by the ten key 8, and the number is set.

  On the left side of the central portion of the standby screen 601 is an external view display area 605 that displays the overall appearance of the image forming apparatus 1 as a schematic view. In this external view display area 605, the apparatus main body, a paper tray, and installed options (RADF 112, various sorters, a large capacity tray, a multistage desk, etc.) are displayed. The paper tray displays the type, size, and remaining amount of the loaded paper.

  On the right side of the central portion of the standby screen 601, there is a finished form display area 606. Here, the finished form of the image formed is schematically illustrated. This finished form indicates what the area of the image formed on the selected paper will be, and the user can prevent this erroneous operation by confirming this. Yes. In the finished form display area 606, conditions that can be expressed as a figure among conditions set by a condition key (described later) that is a touch key can be displayed as appropriate.

  There is a mode display area 604 at the upper left of the external view display area 605. In the mode display area 604, the current mode of the image forming apparatus 1 is displayed. As described above, as described above, any one of the copy mode, the FAX mode, and the printer mode is selected and displayed by operating the mode switching key 12 (the copy mode in FIG. 6). When the numeric keys 8 are operated in a specific order, a setting mode for a serviceman who performs maintenance of the image forming apparatus 1 can be displayed.

  A condition key area 607 is provided below the standby screen 601. In the condition key area 607, a condition key 610 that is a touch key for setting various conditions of the image forming apparatus 1 is arranged. In the present embodiment, a color selection key 610a for selecting a color mode, a copy density key 610b for making settings relating to density at the time of image formation, a paper type / size key 610c for selecting the type and size of paper, An enlargement / reduction key 610d for setting a magnification is provided. The condition key 610 is not limited to these.

  There is a setting content display area 608 in the upper part of the condition key area 607, and the condition selected by the condition key 610 is displayed in the upper part corresponding to each condition key 610. In FIG. 6, “monochrome” is displayed as the condition of the color selection key 610a, “automatic (automatic setting)” is displayed as the condition of the copy density key 610b, and the condition of the paper type / size key 610c is displayed. “Regular paper / automatic (automatic setting)” is displayed, and “100% (original size)” is displayed as the condition of the enlargement / reduction key 610d.

  Further, there is a selection condition display area 609 between the setting content display area 608 and the external view display area 605 and the finished form display area 606. Here, a selection key 611 that can select various conditions corresponding to the condition key 610 when the condition key 610 is operated is displayed.

  For example, as shown in FIG. 7, when the color selection key 610a is operated among the condition keys 610, the selection condition display area 609 includes a monochrome key 611a as a selection key 611, a cyan key 611b as a single color key, magenta. A key 611c, a yellow key 611d, and a full color key 611e are displayed.

  If the monochrome mode is selected, the monochrome key 611a is operated as shown in FIG. Thus, since the monochrome mode is selected, the monochrome key 611a is actively displayed on the display. The active display method is not particularly limited. For example, as shown in FIG. 7, there can be mentioned a method in which the key frame is doubled, but the method is not particularly limited. Another method is to make the frame thick.

  When the image forming apparatus 1 changes from the standby state to the operation setting state, an operation setting initial screen 621 is displayed on the color LCD 6 as shown in FIG. In the operation setting initial screen 621, unlike the standby screen 601 shown in FIG. 6, the image formation number display area 603 is closed, and a finished form display area 606, a condition key area 607, a setting content display area 608, and a selection are displayed. Instead of the condition display area 609, an operation setting content area 622 for displaying operation setting contents is displayed. A mode display area 604 indicates a mode for setting an operation.

  In addition, an external view of the image forming apparatus 1 is displayed in the external view display area 605 in the same manner as the standby screen 601. This external view is used to indicate which function in the apparatus is used when the selected operation setting content is executed. In the operation setting content area 622, setting content keys 623 (γ characteristic key 623a, environmental characteristic key 623b, AE key 623c, paper transport key 623d), an execution key 624, and an end key 625 for selecting operation setting contents are provided. It is displayed.

  Of the setting content keys 623, the γ characteristic key 623a determines how to convert the density input value of the image data into a density output value. The setting of the γ characteristic executed by operating the γ characteristic key 623a will be described later. The environmental characteristic key 623b is a key for setting whether or not to set an image condition in consideration of environmental characteristics, particularly temperature and humidity characteristics. The AE key 623c is a key for performing correction so that the automatic density works appropriately. The sheet conveyance key 623d is a key for setting a setting related to sheet conveyance, for example, a sheet deflection amount in an alignment roller (for example, the registration roller 212 in FIG. 2).

  When the execution key 624 is activated by operating any of the setting content keys 623 and then this key is operated, setting processing of the selected setting content is started. The end key 625 is a key for ending the operation setting state to enter a standby state.

  Next, an operation method for performing the transition from the standby state to the operation setting state and the transition from the standby state to the image forming operation state using the operation panel 5 will be described with reference to the flowcharts of FIGS. I will explain.

  In the standby state in which the standby screen 601 is displayed on the operation panel 5 (step 1; hereinafter, step is abbreviated as S), it is determined whether or not the numeric keypad 8 has been operated in a specific order (S2). If the numeric keypad 8 is not operated in a specific order, it is next determined whether or not the all release key 10 has been operated (S3), and the all release key 10 (abbreviated as AC key in FIGS. 9 and 10) is operated. If so, the process returns to S1, and the standby screen 601 is displayed again. If all the release keys 10 are not operated in S3, it is next determined whether or not the numeric keypad 8 is operated (S4). If the numeric keypad 8 is operated, a numerical value corresponding to the operated numeric keypad 8 is displayed. The number is entered in the number-of-forms display area 603 (S9), and the process returns to S2.

  If the numeric keypad 8 has not been operated in S4, it is next determined whether or not the clear key 9 has been operated (S5). If the clear key 9 has not been operated, 1 is set in the image forming number display area 603. Count (S10) and return to S2. If the clear key 9 is not operated in S5, it is next determined whether or not the condition key 610 is operated (S6). If the condition key 610 is operated, the selection condition display area is displayed as the previous screen. It is determined whether or not the screen (selection screen) on which the selection key 611 is displayed in 609 (S11). If the selection key 611 is displayed, it is determined whether or not the displayed selection screen corresponds to the operated condition key 610 (S13).

  If the selection screen corresponds to the condition key 610 operated in S13, the currently displayed selection screen is closed, the selected condition is displayed in the setting content display area 608 (S14), and the process returns to S2. . If the selection screen is not displayed on the previous screen in S11, the selection screen corresponding to the operated condition key is displayed (S12), and the process returns to S2.

  If the selection screen does not correspond to the operated condition key 610 in S13, the currently displayed selection screen is closed and the selected condition is displayed in the setting content display area 608, and then the operated condition key 610 is displayed. A corresponding selection screen is displayed (S15), and the process returns to S2. If the condition key 610 has not been operated in S6, it is next determined whether or not the selection key 611 has been operated (S7). If the selection key 611 has been operated, the operated selection key 611 is displayed as active. The process returns to S2 (S16).

  If the selection key 611 is not selected in S7, it is next determined whether or not the start key 11 is operated (S8). If the start key 11 is operated, an image forming operation is executed (S17). When the image forming operation is completed, the process returns to S2. If the start key 11 is not operated in S8, the process returns to S2.

  If the numeric keypad 8 is operated in a specific order in S2, the screen of the color LCD 6 is switched to the operation setting initial screen 621 (S18), but the operation setting after S18 will be described later.

  In the operation control from S1 to S17 described above, an example of a screen change after the condition key 610 is operated in S6 will be described. First, on the standby screen 601 shown in FIG. 6, the operation when the color selection set to the monochrome mode among the condition keys 610 is set to the full color mode will be described first.

  When the color selection key 610a in the condition key area 607 is operated, as shown in FIG. 7, in the selection condition display area 609, each condition of monochrome / monochromatic color (cyan / magenta / yellow) and full color which are selection conditions for color selection is displayed. Are displayed as selection keys 611 (611a to 611e, see the above description).

  At this time, since the monochrome condition was selected before the operation of the color selection key 610a, the monochrome key 611a of the selection keys 611 is actively displayed until another selection key 611 is operated. . When the selection key 611 is actively displayed, a ▲ is displayed in the condition display frame (the display frame immediately above the color selection key 610a) in the setting content display area 608, thereby the current condition is being selected. It shows that.

  As shown in FIG. 11, when the full color key 611e is operated in color selection in the selection condition display area 609, the full color key 611e is displayed in an active manner. Next, when the color selection key 610a which is the condition key 610 is operated again, as shown in FIG. 12, the selection key 611 in the selection condition display area 609 is closed, and the condition of the full color key 611e which has been active display. “Full color” is displayed in the display frame immediately above the color selection key 610 a in the setting content display area 608.

  Further, instead of operating the condition key 610 again on the screen of FIG. 11 and closing the selection key 611 in the selection condition display area 609, operating another condition key 610, for example, the paper type / size key 610c, As shown in FIG. 13, the selection key 611 for color selection is closed, “full color” is displayed in the display frame of the setting content display area 608, and the selection key 611 of the paper type / size key 610c is displayed. The

  At this time, ▲ is displayed in the display frame of the setting content display area 608 corresponding to the paper type / size key 610c, indicating that the paper type / size condition is currently selected. The selection key 611 displayed in FIG. 13 is a selection key 611 for selecting a paper, which is a plain paper key 611f, an OHP key 611g, and a coated paper key 611h, and a selection for selecting a paper size. A3 key 611m, B4 key 611n, A4 key 611p, and B5 key 611q, which are keys 611, are displayed.

  Next, the case where the image forming apparatus 1 is in the operation setting state will be described. As described above, if the numeric keypad 8 is operated in a specific order in S2, the color LCD 6 changes from the standby screen 601 to the operation setting initial screen 621. The screen is switched (S18). Then, it is determined whether or not the execution key 624 displayed in the operation setting content area 622 is operated (S19). If the execution key 624 is operated, the operation setting content area 622 is also displayed. The setting process corresponding to the content of the selected setting content key 623 is executed (S23).

  If the execution key 624 is not operated in S19, it is next determined whether or not the all release key 10 is operated (S20), and if the all release key 10 is operated, the process returns to S1. On the other hand, if the all release key 10 is not operated in S20, it is next determined whether or not the end key 625 is operated (S21). If the end key 625 has been operated, the process returns to S1 in the same manner as when all the release keys 10 have been operated.

  If the end key 625 is not operated in S21, it is next determined whether or not the setting content key 623 is operated (S22). If the setting content key 623 is operated, the operated setting content key is determined. 623 is set as an active display (S24). If the setting content key 623 is not operated in S22, the process returns to S19 to wait for the operation of any one of the execution key 624, the all release key 10, the end key 625, or the setting content key 623.

  In the image forming apparatus 1 according to the present embodiment, in order to appropriately form an image of a document read by the image reading unit 110 using the image forming unit 210, the density input value of the image data is converted and the density is changed. It is necessary to decide whether to use the output value. This is because the image forming characteristics of the image forming unit 210 are different for each image forming unit 210. The relationship of the density output value with respect to the density input value is generally called a γ characteristic.

  The γ characteristic is determined before the image forming apparatus 1 is shipped from the factory or when the image forming apparatus 1 is installed. The procedure of this γ characteristic setting process will be described with reference to the flowcharts of FIGS.

  The flowcharts shown in FIGS. 14 and 15 show the procedure when the γ characteristic key 623a among the setting contents keys 623 is operated in the operation setting state (S18 to S24) in the flowchart of the operation method shown in FIGS. It is shown.

  First, when the γ characteristic key 623a in the operation content setting area 622 is operated while the operation setting initial screen 621 is displayed, the γ characteristic key 623a is actively displayed as shown in FIG. Thereafter, when the execution key 624 is operated, a γ characteristic setting process is performed.

  Thereafter, as shown in FIG. 16, a γ characteristic setting initial screen 631 is displayed (S50). This γ characteristic setting initial screen 631 has an automatic key 632a for selecting whether to set the γ characteristic automatically, that is, based on the determination of the image forming apparatus 1 itself, and whether the setting of the γ characteristic is determined manually, that is, the user himself / herself. A γ characteristic selection key 632 including a manual key 632b for selecting is displayed. Further, the above-described execution key 624 and end key 625 are also displayed on the γ characteristic setting initial screen 631.

  On the γ characteristic setting initial screen 631, a key operation of any one of the execution key 624, the end key 625, the automatic key 632a, and the manual key 632b is awaited (a loop connecting S51, S53, S54, S56, and S51). If the end key 625 is operated in S51, the γ characteristic setting process is terminated, the process returns to S18 in the flowcharts of FIGS. 9 and 10, and the operation setting initial screen 621 (see FIG. 8) is displayed in S18. If the automatic key 632a is operated in S54, the automatic key 632a is displayed as active (S57), and the process returns to S51. If the manual key 632b is operated in S56, the manual key 632b is displayed as active (S58), and the process returns to S51. If the execution key 624 is operated in S53, it is next determined whether or not automatic γ characteristic setting (hereinafter, abbreviated as γ setting as appropriate) is selected (S59).

  In S59, if automatic γ setting is not performed, that is, if manual γ setting is selected, it is determined whether or not automatic γ setting has been executed previously (S60). If the automatic γ setting has been executed before in S60, the process proceeds to S77 (3 in FIG. 15). If automatic γ setting has not been executed before in S60, it is notified that manual γ setting is not possible (S61), and the process returns to S51.

  In S60, it is determined whether or not the automatic γ setting has been executed before. When the γ characteristic of the image forming apparatus 1 is set and determined at the factory, the γ setting is manually set before the automatic γ setting. Prevent it and do it automatically first. As a result, it is possible to prevent the setting time of the γ characteristic from becoming long.

  In addition, there are variations in individual characteristics of the constituent units of the image forming stations Pa to Pd such as the chargers 223a to 223d, the transfer units 225a to 225d, the photosensitive drums 222a to 222d, the developing devices 224a to 224d, or the high-voltage transformer. When these constituent means are exchanged, the image forming characteristics of the image forming stations Pa to Pd change because the combination changes.

  Therefore, in S60, it may be determined whether or not automatic γ setting has been executed after replacement of the constituent units of the image forming stations Pa to Pd. This prevents the manual setting of the γ before the automatic γ setting at the time of the γ setting after replacement of the constituent units of the image forming stations Pa to Pd, and automatically performs the setting first. As a result, it is possible to prevent the setting time of the γ characteristic from becoming long.

  If automatic γ setting is selected in S59, then γ setting is automatically executed. In this automatic γ setting, first, the image forming stations Pa to Pd are adjusted (S62).

  The adjustment of the image forming stations Pa to Pd will be described. First, adjustment is performed by appropriately changing the parameters of the image forming stations Pa to Pd. As shown in FIG. 17, when the front side of the image forming apparatus 1 is represented by F and the rear side is represented by R, for example, a high-density toner patch (hereinafter, referred to as a high-density toner patch) (Abbreviated as high density patch) 141.

  A density sensor 140 (see FIG. 4) such as a light detection sensor provided in the pattern image detection unit detects the density of the high density patch 141 and outputs it to the image data processing unit 41. The image data processing unit 41 compares the detected value with a preset reference value, and calculates parameters of the image forming stations Pa to Pd so that the detected value becomes a reference value within a predetermined range.

  As described above, in S62, the density detection value of the high density patch 141 and the parameters of the image forming stations Pa to Pd corresponding to the detected high density patch 141 (the patch is imaged with a predetermined parameter value). The parameter values of the image forming stations Pa to Pd that can appropriately form an image over the entire density range are obtained. Here, the parameter values of the image forming stations Pa to Pd are obtained by representing the entire density region by the detection of the high density patch 141. The high density patch 141 is obtained even if various conditions such as the environment fluctuate. This is because a toner patch having a more stable density can be formed as compared with a toner patch in an intermediate density region or a low density region.

  In the present embodiment, the parameters of the image forming stations Pa to Pd adjusted based on the detected density value of the high density patch 141 are the developing bias voltage and the grid voltage of the scorotron charger, but are not limited thereto. Instead, for example, the charging potential or the power of the writing laser may be used as in the technique disclosed in Japanese Patent Application Laid-Open No. 8-202092.

  In the present embodiment, when adjusting the image forming stations Pa to Pd, the density of the high density patch 141 formed on the photosensitive drums 222a to 222d is detected. However, the present invention is not limited to this. The density of the high density patch 141 transferred onto the transfer conveyance belt 216 may be detected.

  If the parameter adjustment of the image forming stations Pa to Pd is completed in S62, image formation of a reading gradation pattern chart (pattern chart) as shown in FIG. 18 is started (S63). Next, a screen for informing how to set the gradation pattern chart for reading is displayed in a state in which various keys cannot be operated (S64).

  Next, after the image formation of the reading gradation pattern chart is completed (S65), when the image formation of the reading gradation pattern chart is completed, the reading gradation pattern previously displayed on the color LCD 6 is displayed. A display is made so that various keys on the chart set notification screen can be operated (S66).

  The screen displayed on the color LCD 6 in S66 is changed from the γ characteristic setting initial screen 631 to the γ characteristic setting second screen 641, as shown in FIG. This γ characteristic setting second screen 641 is a set screen for setting a gradation pattern chart for reading, and the execution key 624 and the end key 625 on the γ characteristic setting initial screen 631 are displayed as they are. In addition, an external view of the image forming apparatus 1 is displayed in the external view display area 605, and a pattern chart set diagram showing the arrangement state of a gradation pattern chart for reading, which will be described later, is also displayed on the side. Yes.

  The screen displayed on the color LCD 6 in S64 is basically the same as the γ characteristic setting second screen 641, but since various key operations are disabled, the execution key 624, the end key 625, etc. The frame of each key is displayed as a dotted line, or the key color is displayed lightly to indicate that operation is not possible at present.

  Next, it is determined whether or not the end key 625 has been operated on the second gamma characteristic setting screen 641 (S67). If the end key 625 has been operated, the automatic γ setting is stopped (S68), and the process returns to S50 to wait for any key to be operated on the γ characteristic setting initial screen 631. If the end key 625 is not operated in S67, it is determined whether or not the execution key 624 is operated (S69). If the execution key 624 is not operated, the process returns to S67. If the execution key 624 is operated, it is determined whether or not the reading gradation pattern chart (paper) is set at the setting position of the reading gradation pattern chart. (S70).

  If the setting of the sheet is not detected in S70, a notification is made to set the reading gradation pattern chart (S71), and the process returns to S67. If the setting of the sheet is detected in S70, each gradation pattern for reading formed in the gradation pattern chart for reading is read as the gradation pattern chart for reading is set (S72).

  Calculation of the γ characteristics of the image forming stations Pa to Pd is started based on the read density of each read gradation pattern and the dither value associated with each gradation pattern (S73). The calculation of the γ characteristic is started and the current calculation is displayed on the screen (S74). After the calculation of the γ characteristic is completed (S75), when the calculation is completed, the calculated automatic setting is performed. The γ characteristic is displayed on the screen (S76). In S76, a manual setting screen is displayed in order to manually set the γ characteristic. When the calculation of the γ characteristic is thus completed, a visual gradation pattern chart (pattern chart) 200 as shown in FIG. 20 is formed (S77 in FIG. 15).

  Note that the number of gradations of the visual gradation pattern chart 200 shown in FIG. 20 is smaller than the number of gradations of the reading gradation pattern chart described in detail later.

  As described above, in the image forming apparatus 1 according to the present invention, the reading gradation pattern chart is first formed on the sheet based on the first image information (referred to as the first image information), and then the reading image is read. The gradation pattern chart is read as second image information to obtain adjustment information (in this case, γ characteristics), and the image processing condition is adjusted by the image processing unit 2 based on this adjustment information. .

  However, the user's preference or demand for gradation is not satisfied only by the automatic gradation determination as described above. Therefore, it is preferable to determine the gradation using the visual gradation pattern chart 200 as described above. When the reading gradation pattern chart is the first image, the visual gradation pattern chart 200 is the second image.

  Here, in general, when the gradation is determined by the image reading unit, it is possible to determine the gradation more accurately when the number of gradations is larger. However, when the user determines the gradation If the number of gradations is too large, the determination becomes complicated and accurate gradation determination cannot be performed. On the contrary, if the number of gradations is small, it is suitable for the user's determination, but the image reading means cannot make an accurate determination.

  Therefore, as described above, the number of gradations in the visual gradation pattern chart 200 is made smaller than the number of gradations in the reading gradation pattern chart, that is, the number of gradations in the reading gradation pattern chart is visually checked. By making it larger than the number of gradations of the gray scale pattern chart 200, it is possible to realize more accurate gradation determination.

  Here, on the γ characteristic setting second screen 641, before the image formation of the reading gradation pattern chart is completed, a message related to the reading gradation pattern chart and the reading gradation pattern chart are set. The position is displayed. That is, the user can grasp how to set the obtained gradation pattern chart for reading before the image formation is completed.

  As shown in FIG. 19, in the external view of the apparatus displayed in the external view display area 605, where to set the reading gradation pattern chart, the front / back direction and the vertical direction of the reading gradation pattern chart to be set Indicates information related to the gradation pattern chart for reading, such as how to perform.

  Specifically, the mark ▼ is displayed on the document set tray of the RADF 112 (see FIG. 2), and this indicates the set position (set information) of the gradation pattern chart for reading. In the reading gradation pattern chart set at this time, the surface on which the gradation pattern is formed is up, the cyan gradation pattern is on the rear side of the apparatus, and the black gradation pattern is on the front side of the apparatus. Is set to be In the RADF 112, since the reading gradation pattern chart is reversed and conveyed to the contact glass, the surface on which the gradation pattern is formed is shown facing upward when setting.

  By the way, in the conveyance of the reading gradation pattern chart by the RADF 112, the reading gradation pattern chart may become dirty or jammed during the conveyance. Therefore, as shown in FIG. 21, it may be notified that the gradation pattern chart for reading is set directly on the contact glass without using the RADF 112. In this case, the external view of the apparatus shows a state in which the double-sided automatic document feeder 112 is opened, and a ▼ mark is displayed on the part of the contact glass.

  At this time, with respect to the setting direction of the gradation pattern chart for reading, it is set on the contact glass according to the A3 size of the document setting reference plate, and the gradation pattern forming surface side faces downward (that is, the back surface is set upward). The cyan gradation pattern is set to the rear side of the apparatus and the black gradation pattern is set to the front side of the apparatus. This set form is displayed in the pattern chart set form figure.

  Here, the display screen displayed on the color LCD 6 in the above-described process will be described. During the calculation of the γ characteristic in S74, the color LCD 6 displays the γ characteristic setting second screen 641 to the γ characteristic setting third screen 651 as shown in FIG. On this screen, a message area 602 indicates that the γ characteristic is being calculated, and various keys are inoperable (as described above, the various keys are displayed in dotted lines in the inoperable state. )

  Further, after completing the calculation of the γ characteristic in S75, the color LCD 6 displays the γ characteristic setting fourth screen 661 to the γ characteristic setting fourth screen 661 as shown in FIG. In this screen, a CMYK density key 662 is provided so that a γ characteristic can be displayed for each color. In FIG. 23, a cyan density key 662a, a magenta density key 662b, a yellow density key 662c, and a black density key 662d are calculated. Four keys are included.

  By operating the CMYK density key 662, the γ characteristic of the color corresponding to the operated key is displayed in a γ characteristic graph in which the vertical axis is the image forming density and the horizontal axis is the adjustment point. In FIG. 23, since the cyan density key 662a is operated, the γ characteristic of cyan is displayed in a graph.

  Further, on the fourth γ characteristic setting screen 661 shown in FIG. 23, the calculated γ characteristic for each color is displayed in a graph, and at the same time, the hues of cyan, magenta, yellow, and black can be adjusted according to the user's preference. It has become. Specifically, the user can adjust the hue of each of the colors while viewing the visual gradation pattern chart 200 obtained in S77 described above. For this reason, the fourth screen 661 for setting the γ characteristic is displayed. A density up key 663a, a density down key 663b, an adjustment point up key 664a, and an adjustment point down key 664b are provided.

  In FIG. 23, the density up key 663a and the density down key 663b are provided below the CMYK density key 662, and are used to adjust the density of the color selected by the CMYK density key 662. The adjustment point up key 664a and the adjustment point down key 664b are used to move the adjustment point on the horizontal axis in the γ characteristic graph, and are provided below the γ characteristic graph in FIG.

  The adjustment point of the γ characteristic graph and the gradation pattern of the visual gradation pattern chart 200 correspond to each other. Therefore, by moving the adjustment point with the adjustment point up key 664a and the adjustment point down key 664b, a desired gradation in the visual gradation pattern chart 200 can be obtained while the user visually observes the visual gradation pattern chart 200. The density of the pattern can be changed according to the user's preference.

  The manual setting of the γ characteristic will be described based on the flowchart of FIG. As shown in FIG. 15, after the visual gradation pattern chart 200 is formed in S77, an end key 625, an execution key 624, a CMYK density key 662, respectively in S78, S79, S80, S81, S82, S83, and S84. It is determined whether or not the density up key 663a, the density down key 663b, the adjustment point up key 664a, and the adjustment point down key 664b are operated.

  If the end key 625 is operated in S78, it is determined whether or not manual setting of the γ characteristic has been made (S85). If there is no manual setting, the γ characteristic setting process is ended. As a result, S23 in the flowcharts of FIGS. 9 and 10 ends, and therefore, the process returns to S18.

  If manual setting has been made in S85, a message is displayed on the screen to select whether or not to replace the target density of the γ characteristic (image formation density at a predetermined adjustment point in the γ characteristic graph) with this manually set value. (S86), it is determined whether or not the execution key 624 is operated (S87). If the execution key 624 is operated, the target density is replaced with the manually set value (S89), and the γ characteristic setting process is terminated. On the other hand, if the execution key 624 is not operated in S87, it is next determined whether or not the end key 625 is operated (S88). If the end key 625 is operated, the γ characteristic setting process is ended. If there is no operation of the end key 625 in S88, it returns to immediately before S87 and waits for the operation of the execution key 624 or the end key 625.

  If the execution key 624 is operated in S79, the visual gradation pattern chart 200 is formed again on the basis of the γ characteristic adjusted on the screen (S90), and the process returns to S78. In S80, if the CMYK density key 662 is operated, the operated CMYK density key 662 is actively displayed (S91), and then the γ characteristic of the color corresponding to the operated CMYK density key 662 is displayed on the graph. (S92), the process returns to S78.

  If the density up key 663a is operated in S81, the density of the adjustment point that is actively displayed in the γ characteristic graph is increased by one (S93), and the up / down key operable / impossible display switching process (described later) is executed. After (S94), the process returns to immediately before S78.

  If the operation of the density down key 663b is performed in S82, the density of the adjustment point that is being actively displayed is decreased by one scale (S95), and the up / down key operation enable / disable display switching process is executed (S94), and then the process goes to S78. Return.

  If the adjustment point up key 664a is operated in S83, the active adjustment point is moved up by one from the current adjustment point (S96), and the up / down key operation enable / disable display switching process is executed (S94). Return to immediately before S78.

  If the adjustment point down key 664b is operated in S84, then it is determined whether or not the adjustment point down key 664b is inoperable display (S97), and the active adjustment point is moved down by one from the current adjustment point ( (S98) After the up / down key operation enable / disable display switching process is executed (S94), the process returns to S78.

  Note that it is determined whether or not the adjustment point down key 664b is inoperable display in S97 because the active adjustment point is the adjustment point on the screen displayed in S76 (the screen shown in FIG. 23). Therefore, even if the adjustment point down key 664b is operated in this state, there is no adjustment point below this, so that it cannot be moved.

  Here, the up / down key operation enable / disable display switching process will be described with reference to the flowchart of FIG.

  In this up / down key operation enable / disable display switching process, the image forming density or the adjustment point becomes the upper limit value by operating the density up key 663a, the density down key 663b, the adjustment point up key 664a, and the adjustment point down key 664b. Sometimes the key to increase the density or adjustment point (hereinafter referred to as the up key) is displayed inoperable, and the key to decrease the density or adjustment point when the image formation density or adjustment point reaches the lower limit (hereinafter referred to as the “up key”). This is a process for displaying “down key” inoperable.

  In addition, in the up / down key operation sensitive / impossible display switching process, when one of the up key or the down key is in an inoperable display and the other operable key is operated, the inoperable display state of the inoperable key is changed. It can also be released to make it operable.

  When the up / down key operation enable / disable display switching process is started, it is determined whether or not the target to be operated with the up key after the operation of the up key or the down key is an upper limit value (S100). If the upper limit value is reached, the up key is disabled (S101), and the up / down key operable / impossible switching process is terminated. If the upper limit value is not reached in S100, it is next determined whether or not the target to be operated with the up key is the upper limit value after the up key or down key is operated (S102). Then, the down key is disabled (S103), and the up / down key operable / impossible display switching process is terminated. In S102, if the value of the operation target of the down key immediately after the key operation is not the lower limit value, it is next determined whether or not the value of the operation target of these keys immediately before the operation is the upper limit value using the up key or the down key. (S104). If it is an upper limit value, it is determined whether or not the operation key is a down key (S105). If it is a down key, the operation disable display of the up key is canceled and the operation key is displayed (S106). Thus, the up / down key operation enable / disable display switching process is completed. If the operation key is not the down key in S105, the up / down key operation enable / disable display switching process is terminated.

  If the value of the operation target of these keys immediately before the operation of the up key or the down key is not the upper limit value in S104, then whether the operation target value of these keys immediately before the operation of the up key or the down key is the lower limit value. It is determined whether or not (S107). If it is the lower limit value, it is determined whether or not the operation key is an up key (S108). If the operation key is the up key, the operation disable display of the down key is canceled and the operation is displayed (S109), the up / down key operation capability / impossible display switching process is terminated, and the operation key is not the up key. Then, the up / down key operable / impossible display switching process is terminated.

  Next, the manual setting of the γ characteristic will be described more specifically. For example, first, a cyan γ characteristic graph is displayed as shown in FIG. 23, and then it is desired to increase the density of the magenta adjustment point 10 by visual confirmation of the visual gradation pattern chart 200. At this time, the magenta density key 662b of the CMYK density keys 622 on the fourth γ characteristic setting screen 661 shown in FIG. 23 is operated to display a magenta γ characteristic graph as shown in FIG.

  Next, in order to improve the density of the magenta adjustment point 10, the active adjustment point is adjusted to the adjustment point 10 by operating the adjustment point up key 664a on the screen (gamma characteristic setting fourth screen 661) shown in FIG. (See FIG. 26). Next, as shown in FIG. 26, the image forming density at the adjustment point 10 is increased by operating the density up key 663a (see FIG. 27). As a result, as shown in FIG. 27, the density at the magenta adjustment point 10 is readjusted to an appropriate density by visual confirmation by the user. In this way, the density of each color and each adjustment point can be manually adjusted for each adjustment point.

  That is, the density up key 663a, the density down key 663b, the adjustment point up key 664a and the adjustment point down key 664b displayed on the fourth γ characteristic setting fourth screen 661, and the γ characteristic setting fourth screen 661 are set. The execution key 624 for executing the contents is a manual input unit for manually inputting image information. The manual input unit and the image reading unit 110 (image reading unit) are used to perform an image in the image forming apparatus 1 according to the present invention. An information input means is configured.

  The range that can be adjusted by the manual adjustment is preferably defined in advance. That is, an adjustment upper limit value and an adjustment lower limit value are provided at a certain adjustment point, and it is preferable that the density cannot be changed beyond that. In this case, the upper limit value of the adjustment point is a value smaller by a predetermined amount than the current density of the adjustment point above it. On the other hand, the lower limit value of the adjustment point is a value larger by a predetermined amount than the current density of the adjustment point below it. The upper limit value and the lower limit value are set in this way because the density difference is less than a predetermined value between the adjustment points, preventing the multi-tone from being appropriately expressed and increasing the density of the lower adjustment point. This is so as not to exceed the density of the adjustment point.

  For example, as shown in FIG. 28, when looking at the adjustment lower limit value and the adjustment upper limit value at the adjustment point 10, the adjustment point upper limit value is smaller by a predetermined amount than the density of the high density side adjacent adjustment point (adjustment point 11). The adjustment point lower limit value is set to a value larger by a predetermined amount than the density of the low density adjacent adjustment point (adjustment point 9). Therefore, the density of the adjustment point 11 or the adjustment point 9 that is an adjacent adjustment point and the density of the adjustment point 10 are not reversed, and as a result, the gradation of image formation can be ensured.

  As described above, in the image forming apparatus 1 according to the present invention, not only the γ characteristics are automatically set, but also the user uses the visual gradation pattern chart 200 to obtain a specific hue in a specific density range. It becomes possible to make it stronger or weaker. As a result, color correction according to the user's request can be performed.

  Although not shown in this embodiment, if a specific hue is to be strengthened over the entire region of the γ characteristic, a key for shifting the density value in the γ characteristic graph up and down over all the adjustment points is provided to adjust the hue. You may go. Further, several continuous adjustment points may be adjusted together to save the adjustment effort.

  In this embodiment, if the execution key 624 is operated in S89, the target density is replaced with the manually set value, but the manually set density value is originally stored as the target density value. It may be stored separately from the target density, and the γ characteristic may be set using either one according to the situation.

  The target density originally stored is a standard value that does not take into account the user's preference, but the manually set density value is replaced with the target density value by manual adjustment. The value is reflected. Therefore, the usage of each target density value is as follows.

  First, since the user is not limited when the image forming apparatus 1 is shipped from the factory, it is not necessary to consider the user's preference, and adjustment is performed with a standard target density value. After that, when the image forming apparatus reaches the user and is installed, the user's preference needs to be taken into account and reflected, so the manually set density value is replaced with the target density value. In this case, when setting the γ characteristic using the reading gradation pattern chart, the target density value that already reflects the user's preference is used. Therefore, it is possible to save the trouble of manually adjusting the γ characteristic according to the user's preference by looking at the visual gradation pattern chart 200.

  When the user moves the image forming apparatus 1 to another department, the initially set target density value reflects the preference of the user of the previous department, and a new department It will be different from your preference. Therefore, when the installation location of the image forming apparatus 1 is moved, it is only necessary that the original standard target density can be selected.

  Next, the reading gradation pattern chart will be described. As shown in FIG. 18, the above-described reading gradation pattern chart 100 includes 32 gradation patterns 101..., For example, A3 corresponding to four colors of CMYK, each having 16 different densities in two columns. Formed on a size paper.

  A background density measuring unit 102 for measuring the background density of the paper is provided at the end of the reading gradation pattern chart 100 on the low density side (light side). As will be described later, the density of the gradation patterns 101 of each color arranged in two rows is light in the left column and dark in the right column. Further, when the reading gradation pattern chart 100 is set, the direction of each color and shading (density change direction) is a gradation pattern so that the association with the setting direction displayed on the color LCD 6 becomes simpler. 101...

  The reading gradation pattern chart 100 is formed based on the pattern information which is the first image information described above. The pattern information may be generated as appropriate by the pattern information generating means, or stored in the hard disks 43a to 43d (see FIG. 3) in the image memory 43 in association with the dither value and the image formation position information. Also good.

  When forming the image of the reading gradation pattern chart 100, first, pattern information of the gradation patterns 101... Read from the hard disks 43a to 43d is transferred to the LCU 42a via the image data bus. Under the control of the LCU 42a, electrostatic latent images are formed on the photosensitive drums 222a to 222d (see FIG. 2) by the LSUs 42b, 42c, 42d, and 42e of the respective colors. On the paper, individual gradation patterns 101 are formed at positions corresponding to the pattern information with dither values corresponding to the pattern information.

  By the way, among the characteristics related to image formation of the electrostatic image forming stations Pa to Pd, there is a phenomenon that the portion where the potential of the electrostatic latent image changes rapidly becomes higher than the original density. Specifically, a strong electrostatic electric field acts on the boundary portion of the electrostatic latent image of line drawing or area drawing. On the other hand, in an electrostatic latent image having a large area such as a portion other than the boundary portion such as the center in the surface image, the electric field becomes weak and is difficult to be developed in the development process. For this reason, the boundary part may have a higher density than the center, particularly in a plane image. This is generally called an edge effect.

  In other words, this edge effect is because the potential difference increases at the end (boundary part) of the image of the surface image, and the electric field is emphasized and tends to increase. Conversely, the potential difference is not large at the center of the surface image. This is a phenomenon that occurs when the electric field tends to be low. Therefore, when the gradation pattern 101, which is a plane image, is formed, the edge effect causes the edge of the gradation pattern 101 to have a higher density than the original density, but compared to the main scanning direction of image formation, In the sub-scanning direction, the region where the density becomes higher becomes wider.

  Note that the sub-scanning direction of image formation is a direction along the rotation direction of the photosensitive drums 222a to 222d in the image forming unit 210, and the main scanning direction is along the rotation direction of the photosensitive drums 222a to 222d. This is a direction orthogonal to the direction (sub-scanning direction).

  As described above, the edge effect has a boundary at a portion where the density difference suddenly increases, that is, at a portion where the potential difference of the electrostatic latent images on the photosensitive drums 222a to 222d is greatly different. This occurs because the electric field concentrates on the toner and unnecessarily collects toner during development.

  As for the sub-scanning direction of the gradation pattern 101, the edge that is developed first tends to have a wider area where the density is higher than the edge that is developed later. For example, as shown in FIG. 29, the direction in which development is performed first (that is, the sub-scanning direction) is an arrow P direction, and the background density measuring unit 102, the density 1 gradation pattern 101a, and the density 2 gradation pattern 101b. Further, it is assumed that the gradation pattern 101n of density N is developed in this order. Note that the main scanning direction, which is the direction orthogonal to the sub-scanning direction, is the arrow Q direction in FIG.

  It should be noted that the density of the gradation patterns 101 increases as the density 1 changes to the density N. Also, as shown in FIG. 30, the P direction is the rotation direction of the photosensitive drums 222a to 222d, and development is performed by developing rollers 2241a to 2241d on which electrostatic latent images formed on the surface are opposed to each other. Is done. Accordingly, with the rotation of the photosensitive drums 222a to 222d, a constant width region (development width) along the main scanning direction is gradually developed in the sub scanning direction.

  At this time, as can be seen from the lower graph of FIG. 29, the edge on the side adjacent to the background density measuring unit 102 in the density 1 gradation pattern 101a is closer to the side adjacent to the density 2 gradation pattern 101b. The high density region is wider than the edge. The same applies to the gradation pattern 101b with density 2 and the gradation pattern 101n with density N.

  That is, when the gradation pattern 101 having a high density (dark) is formed in this order from the low density (light) gradation pattern 101 subsequent to the background density measurement unit 102, the gradation pattern 101 in the sub-scanning direction is formed. The region where the edge side (that is, the boundary portion) developed first becomes higher in density than the edge side developed after the sub-scanning direction becomes wider. In addition, the edge side of the gradation pattern 101 that is developed after in the sub-scanning direction has a wider area where the density is higher than the edge in the main scanning direction. As described above, the density difference between the density of the region where the density of the gradation pattern 101 is high and the original density of the gradation pattern 101 increases as the density difference at the edge of the gradation pattern 101 increases.

  Further, as shown in FIG. 31, for example, when each gradation pattern 101 is divided by providing a boundary portion 103 made of white or black between the gradation pattern 101a of density 1 and the gradation pattern 101b of density 2 Even in this case, a boundary portion 103 or a portion where the density difference of the gradation pattern 101 becomes high due to the density difference between the boundary pattern 103 and the adjacent gradation pattern 101 occurs.

  As described above, if there is a density higher than the original density in one gradation pattern 101, the density of the gradation pattern 101 is read and the parameters of the image forming stations Pa to Pd such as the developing bias and the grid are set. Inconvenience occurs when adjusting or setting γ characteristics.

  For example, when the image reading means (image information input means) such as the CCD 116 reads the reading gradation pattern chart 100, a plurality of locations are read with respect to one gradation pattern 101, and the read values are averaged to obtain a final result. A correct reading is output. This is to cope with variations in reading accuracy (input accuracy) of individual light receiving element portions in the CCD 116 and the entire CCD 116, and density accuracy of image formation in the image forming stations Pa to Pd.

  Further, in the reading gradation pattern chart 100, the larger the number of gradation patterns 101 with different densities, the more advantageous is the parameter adjustment and the determination of the γ characteristic in the image forming stations Pa to Pd.

  Here, if there is a portion having a density higher than the original density in one gradation pattern 101, the final read value varies. Therefore, if the gradation pattern 101 is formed to be large, the region of the portion having a higher density than the original density is relatively small, so that the above disadvantage does not occur theoretically. However, in practice, when the size of one gradation pattern is increased so that the area of the original density in one gradation pattern 101 is enlarged, a sufficient number of gradations are formed on one sheet of paper. The patterns 101... Cannot be formed, and the density of the gradation patterns 101... Varies due to variations in the formation densities of the image forming stations Pa to Pd (that is, image formation accuracy) and variations in paper characteristics. The density reading of ... will be inaccurate.

  Further, as a characteristic relating to image formation in the image forming stations Pa to Pd, there is a toner concentration replenishment followability. That is, in general, the toner density of the developing devices 224a to 224d is determined based on the density of a specific representative point, and it is further determined whether or not to newly supply toner based on this density. . For this reason, if there are continuous high-density portions in the sub-scanning direction of the gradation pattern 101 for each column of the gradation patterns 101 arranged in the main scanning direction, the high-density portions are continuous. In the column of the gradation pattern 101 in the main scanning direction, the toner concentration in the column of the gradation pattern 101 in the main scanning direction in which other high density portions do not continue even though the toner density is lower than the original value. Will be in the state of being appropriate.

  On the contrary, the toner is replenished due to the continuous high density portion, and a portion showing a toner density value higher than the original is generated, and in this portion, the density of the developed gradation pattern 101 is the original density. May be higher than concentration. Further, regarding each of the CMYK image forming stations Pa to Pd, the formation density of the reading gradation pattern chart 100 is divided into a color portion having an original density and a color portion having no original density. As a result, the balance between colors cannot be set appropriately.

  Therefore, in the image forming apparatus 1 according to the present invention, each gradation pattern is avoided so as to avoid the enhancement of the electric field due to the potential difference at the boundary portion in the electrostatic latent image of each gradation pattern 101 and 101 adjacent in the sub-scanning direction of image formation. The image information 101 is determined in advance in consideration of the image forming characteristics of the image forming unit 210, and is stored in the hard disks 43a to 43d and the like.

  Specifically, as shown in FIGS. 18 and 1, the reading gradation pattern chart 100 according to the present invention includes 16 gradation patterns 101 in one row in the sub-scanning direction in the main scanning direction for each color of CMYK. Two rows are formed, and the gradation pattern 101 is arranged so that the gradation pattern 101 is changed from the low density to the high density side along the sub-scanning direction. A plurality of adjacent ones are arranged in the main scanning direction.

  In FIG. 1, the numbers entered in each gradation pattern 101 indicate the order of density values of the gradation pattern 101. In this case, the smaller the number, the lower the density (lighter). Yes.

  The density of the gradation patterns 101... In the reading gradation pattern chart 100 is low density to high density in the sub-scanning direction side, and the gradation pattern 101 having a density close to the main scanning direction is adjacent. However, the specific density order is such that gradation patterns 101 and 101 having adjacent densities in the main scanning direction are arranged, and the next density is applied to the gradation pattern 101 adjacent in the sub-scanning direction. Each gradation pattern 101 is arranged.

  That is, when viewed from the lighter side, for example, in cyan, the gradation patterns of density 1 and 2 are arranged adjacent to the main density in the main scanning direction next to the background density measuring unit 102, and the density becomes higher in the sub-scanning direction side. The gradation patterns of density 3 and 4 are arranged. In other words, in the reading gradation pattern chart 100, the order of density of the gradation patterns 101 is staggered.

  If the arrangement of the gradation pattern 101 in the reading gradation pattern chart 100 is as described above, the gradation pattern 101 having a large density difference in the sub-scanning direction during image formation of the reading gradation pattern chart 100. Are not lined up. For this reason, the influence of the edge effect (reduction in the area of the original density) can be further reduced. In addition, since the high-density gradation pattern 101 having a closer density is not continuous in the sub-scanning direction, it is possible to appropriately cope with the toner replenishment followability.

  The reading gradation pattern chart 100 is arranged so that the gradation patterns 101 adjacent in the sub-scanning direction of image formation are in direct contact with each other. As a result, the boundary portion 103 made of white or black is not provided between the gradation patterns 101 and 101 arranged in the sub-scanning direction. Therefore, the influence of the edge effect by these boundary portions 103 can be avoided.

  Here, in the reading gradation pattern chart 100 as shown in FIG. 1, the density difference between the background density measuring unit 102 and the density 1 gradation pattern 101 or the density 2 gradation pattern 101 is not so large. However, since such densities 1 and 2 are very light density ranges, there is a possibility that the difference from the original density may be increased due to the edge effect as compared with the high density gradation pattern 101. Similarly, since the density difference between the gradation pattern 101 with the density 31 and the gradation pattern 101 with the density 32 and the ground is very large, the edge effect may be prominent.

  Therefore, it is preferable that a dummy pattern having a density close to the gradation pattern 101 serving as the end is formed adjacent to the gradation pattern 101 serving as the end in the sub-scanning direction. Thus, for example, as shown in FIG. 32, the gradation patterns 101 and 101 having the density 1 and 2 and the gradation patterns 101 and 101 having the densities 31 and 32 and the ground (ground density measurement) in the reading gradation pattern chart 100 A dummy gradation pattern (hereinafter referred to as a dummy pattern) 131 is disposed between the first and second portions 102).

  The dummy pattern 131 may have a density close to or the same as that of the gradation patterns 101 of density 1 and 2, or 31 and 32, but the dummy pattern is adjacent to the high density gradation pattern 101. When disposing 131, it is preferable to slightly lower the density of the dummy pattern 131 in consideration of toner replenishment followability. In the dummy pattern 131 of the high density gradation pattern 101, the toner replenishment followability is considered on the side where a plurality of types of reading gradation pattern charts 100 are formed or the high density side is developed first. It is necessary in some cases.

  For example, in FIG. 32, the dummy pattern 131 adjacent to the gradation patterns 101 of the density 1 and 2 on the lighter side has the same density (density 1 and 2), but the density 31 on the darker side. The dummy patterns 131 adjacent to the gradation patterns 101 and 32 have densities 29 and 30 that are slightly lower in density.

  Further, the arrangement of the gradation pattern 101 in the sub-scanning direction is not limited to the arrangement in which the density order is skipped every one as shown in FIG. 1 and FIG. If the density difference is within the range where there is no influence of the follow-up performance, the arrangement may be randomly arranged as shown in FIG. 33, or the column in the main scanning direction of the gradation pattern 101 may be arranged as shown in FIG. You may arrange | position at random, after making it 3 rows instead of 2 rows.

  That is, in the reading gradation pattern chart 100, the gradation pattern 101 is arranged from the low density to the high density side along the sub-scanning direction of the image formation, and the gradation patterns 101 and 101 having the closest densities to each other. What is necessary is just to make it arrange | position adjacent to each other in the main scanning direction.

  The edge effect and toner replenishment follow-up property are the development method of the developing devices 224a to 224d of the image forming stations Pa to Pd, the development bias value, the charging potential of the photosensitive drums 222a to 222d, and the development for supplying toner to the electrostatic latent image If the diameter of the rollers 2241a to 2241d and the rotation speed of the developing rollers 2241a to 2241d or the development of the two-component method, the toner replenishing method in the developer, the stirring performance for uniformizing the toner density in the developer, Depending on the position of the toner density sensor for detecting the toner density of the toner, the change value of the toner density in the development before the toner replenishment signal is output from the toner density sensor, etc., variously change.

  Therefore, based on the actual characteristics of the individual image forming stations Pa to Pd and the developing devices 224a to 224d, the influence of the edge effect and the toner replenishment followability due to the density difference between the gradation patterns 101 and 101 in the sub-scanning direction. It is only necessary to determine the pattern information (including the dither value and position information) of the gradation pattern 101 in advance so that the influence of the above can be suppressed.

  Each gradation pattern 101 and background in the reading gradation pattern chart 100 (the background density measuring unit 102 is read by each element of the CCD 116, and the read value is stored in storage means such as the hard disks 43 a to 43 d in the image memory 43. If one gradation pattern 101 is read in the n number in the sub-scanning direction and m in the main scanning direction, as shown schematically in FIG. If A is A, the area surrounded by the four points A11, A1n, Am1, and Amn is the entire reading area.

  Of these, the area surrounded by Acd, Aek, Abl, and Aij is the original density area (original density area 101α), and the area corresponding to the high density area due to the edge effect ( In the figure, there is a hatched portion and a high concentration region 101β). That is, one gradation pattern 101 includes a region having a high density due to the edge effect.

  Therefore, in order to obtain a more accurate reading value, a high density region 101β having a greatly different reading value is calculated from the reading value of the entire gradation pattern 101, and the reading value of the original density region 101α other than the high density region 101β is calculated. From this, it is preferable to sample a predetermined number of read values and take the average value to determine the read value of the corresponding gradation pattern 101. Although the predetermined number of samplings is not particularly limited, in this embodiment, for example, there are 256 points of 16 (main scanning direction) × 16 (sub-scanning direction).

  By the way, the gradation pattern 101 is formed with a known dither value as described above. Depending on how the read value is sampled with respect to the dither matrix size of the dither value of the gradation pattern 101, It is possible to prevent reading values from being unnecessarily varied.

For example, the image forming density of the image forming unit 210 in the image forming apparatus 1 is 600 dpi and the resolution of the image reading unit 110 corresponds to 600 dpi. As shown in FIG. It is assumed that the dot D (D ₁ , D ₂ , D ₃ , D _{4 in the} figure) is composed of a 2 × 2 dither matrix in which two dots D are arranged vertically and horizontally. At this time, since the size of one dot of the writing laser (LSU 42b, 42c, 42d, and 42e) in the image forming unit 210 is the same as the size that can be read by one element of the CCD 116, one pixel 201 is set to 2 × 2. In the case of a dither matrix, the reading area of one element of the CCD 116 corresponds to ¼ of the pixel 201.

  Therefore, as shown in FIG. 36B, if the read value of the element of the CCD 116 is used as it is as the read value of the gradation pattern 101, the read value varies greatly depending on the relative position between the CCD 116 and the pixel 201. Therefore, in the present embodiment, in order to prevent this, the reading values of the elements of the four adjacent CCDs 116 are determined based on the reading values of the elements of the CCD 116 stored in the storage means such as the image memory 43. Calculation is performed so that the read value of the gradation pattern 101 is obtained.

That is, as shown in FIG. 36B, among the reading values of each area of the gradation pattern read by the CCD 116, the reading values of two adjacent areas in the sub-scanning direction and the main scanning direction are added together. This is 1/4, and this is used as the reading value of the CCD 116 element. Specifically, D ₁ + D ₂ = D ₁₂ , D ₁ + D ₃ = D ₁₃ , D ₂ + D ₄ = D ₂₄ , and D ₃ + D ₄ = D ₃₄ are each 1/4.

  In this case, since the gradation pattern 101 is read through an image filter of the same size as the dither matrix of the gradation pattern 101, such a reading operation is generally performed by “an image filter is added to the reading value of the CCD 116”. Read through. " As a result, the reading value of the element of the CCD 116 does not vary greatly depending on the relative relationship between the element and the pixel 201, and therefore an appropriate reading value can be obtained.

  Further, when reading a general document, shading correction is performed in which an output value is determined by determining a white level with respect to a read value of the CCD 116 based on a value obtained by reading the reference white plate with the CCD 116. Here, when the reading gradation pattern chart 100 is read, based on the reading value of the reference white plate, when the ground on which the gradation pattern 101 is formed has a higher whiteness than the reference white plate, This causes a problem that the white level cannot be determined appropriately.

  Therefore, in the present embodiment, among the reading values read by the CCD 116, the output value of the base reading value is processed so as to correspond to the zero value. This makes it possible to determine the white level appropriately. As a process for making the reading value of the background correspond to the zero value, specifically, the following method can be cited.

First, when the whiteness of the reference white plate is set to be sufficiently higher than the background of the reading gradation pattern chart 100, the reading value of the gradation pattern 101 is subtracted from the value read by the CCD 116. do it. On the contrary, when the whiteness of the reference white sheet is less than whiteness for the underlying gradation pattern chart 100 reading, for example, as shown in the graph b ₁ in FIG. 37, the "gradation pattern 1" Since the read value (CCD output value in the figure) is lower than the zero value, the read value of the gradation pattern 101 that cannot be used as the read value of the CCD 116 is included.

  Therefore, when the gradation pattern 101 is read by the CCD 116, the reading value of the CCD 116 is reduced by reducing the lamp light amount irradiated to the document (gradation pattern chart 100) or reducing the reading gain of the CCD 116. The reading value lowering operation is performed so that the reading value is smaller than the actual value. At this time, as the reading value of the reference white plate by the CCD 116, the reading value of the CCD 116 is the reading value before the reading value lowering operation as described above (that is, the original reading value).

  As described above, when the whiteness of the reference white plate is lower than the whiteness of the background, the background density of the reading gradation pattern chart 100 read by the CCD 116 is the zero value of the read value (CCD output value) of the CCD 116. The read value lowering operation as described above is performed so that the background density is obtained as the output value of the CCD 116 when the background is read by the CCD 116.

Readings CCD116 obtained as a result, that the output value of the CCD116, as shown in the graph b ₃ in FIG. 37, background density is larger than zero value. Thereafter, as shown in FIG. 37, the entire read value may be shifted by the background read value (arrow B in the figure) by the image processing unit 2. As a result, even when the whiteness of the reference white plate is lower than the whiteness of the background density of the reading gradation pattern chart 100, the CCD 116 can read the background density. As a result, the gradation pattern 101 can be read more stably by making the input density of the gradation pattern 101 to the background more appropriate.

In FIG. 37, the vertical axis indicates the output from the CCD 116, and the horizontal axis indicates the density order of the gradation pattern 101. A graph b ₁ shows a value obtained by reading the background without reducing the read value of the CCD 116 when the whiteness of the background is higher than that of the reference white plate. Graph b ₂ shows a graph in which the above-mentioned graph b ₃ is shifted and the reading value of the background is set to zero.

  In the above-described example, the processing method for obtaining the reading value in which the white level reference is set to the output level of the CCD 116 is shown as the processing for appropriately determining the white level. However, the processing method is not limited to this. The white level can also be obtained from the output level of the CCD 116.

  For example, if the output level of the CCD 116 corresponding to the ground is Sc and the output level of the CCD 116 of each gradation pattern 101 is Tc, the output level Sc of the CCD 116 is added to the output level Tc of each gradation pattern as shown in FIG. Will be. Here, assuming that the maximum value of the number of gradations to be output is n and that n is applied to Sc, the correction value Sn for the white level of the background is obtained from the following equation.

Sn = n − {(n−Tc) / (n−Sc)} × n
The gradation number n is the maximum number of gradations that can be formed by the image forming apparatus 1, and is not limited to a specific numerical value. For example, in this embodiment, since it is assumed that an image with 256 gradations is formed, the maximum value n of the gradations is n = 255 (since 256 gradations, 0 to 255 gradations). Become.

  In this way, the relationship between the dither value in the gradation pattern 101 and the read value in the gradation pattern 101 is obtained as a substantially straight line as shown in FIG. In FIG. 38, the horizontal axis represents the dither value of the gradation pattern 101, which is from 0 to 1020 (an arbitrary value in the middle is represented by xi). The vertical axis is the read value of the gradation pattern (arbitrary value is yi). Further, in the figure, x marks are read values corresponding to the 32 kinds of dither values used in the read gradation pattern 101. In this way, the relationship between the dither value and the read value of the gradation pattern 101 shown in FIG. 38 is determined.

  Further, as shown in Table 1, in addition to the relationship, a standard gradation pattern chart (image formation with a dither value is not necessary, and a standard density pattern chart indicating a standard density may be used) may be used. The read value of the input density when read by the CCD 116, that is, the target read value (target input value, referred to as the target density in the flowchart of FIG. 15 and the description thereof), and the white level is defined for this target read value. The relationship between the output value of the CCD 116 having 256 gradations, that is, the reading reference value (input reference value) is determined in advance by experiments or the like.

  The relationship between the target reading value shown in Table 1 and the reading reference value of the CCD 116 is stored in various storage means of the image forming apparatus 1 as a relationship table (correspondence table). This relationship table requires a smaller memory capacity than the relationship of the reference γ characteristic, and can always easily obtain the optimum γ characteristic. The reading reference value is an input value to the image forming unit 210. More specifically, it is an input value to the image data processing unit 41 shown in FIG. The values in the relationship table between the target reading value and the reading reference value may be about 10 sets, for example.

  For the determination of the γ characteristic, the relationship shown in FIG. 38, that is, the reading formed by the image forming unit 210 with respect to the target reading value corresponding to the reading reference value (the output value of the CCD 116) in the relationship table. The gradation pattern chart is read, and the dither value of the gradation pattern 101 is determined from the obtained relationship.

  That is, from the relationship between the target reading value in Table 1 and the output value of the CCD 116, an arbitrary target reading value is traced from the reading value of the gradation pattern 101 in FIG. If the closest dither value is obtained from the substantially linear relationship in FIG. 6 and is associated with the output value of the CCD 116 corresponding to the target read value (same as the input value to the image forming unit 210), the curve as shown in FIG. A relationship is obtained.

  In FIG. 39, the vertical axis is the dither value (maximum 1020), and the horizontal axis is the output value of the CCD 116 (maximum 255, that is, 256 gradations). It is possible to adjust the image processing conditions to appropriately determine the relationship between the input value and output value relating to image information and density, that is, the γ characteristic.

  In this embodiment, the relationship table between the target reading value and the reading reference value is determined in advance and stored in the storage unit. However, the standard density chart is used for the target image forming apparatus for setting the γ characteristic. The read value may be used as a reading reference value, and the relationship table between the target reading value and the reading reference value may be created by inputting the density of the standard density chart to each value.

  In the above-described embodiment, when the dither value of the gradation pattern 101 is read by the image reading unit 110 when the image forming unit 210 forms a gradation pattern chart and reads it by the image reading unit 110. , And image formation in the image forming unit 210 may vary.

  That is, the density of the gradation pattern when the reading gradation pattern chart 100 is image-formed by the image forming unit 210 varies depending on the image formation accuracy at the density of the image forming unit 210 and is the same reading gradation pattern chart. The read value when 100 is read by the image reading unit 110 also varies depending on the density reading accuracy of the image reading unit 110. Due to both variations, the gradation pattern 101 which is originally on the high density side in the reading gradation pattern chart 100 is reversed so that the read value becomes a low value (a value corresponding to the low density side). End up.

  Therefore, if a value in which the reverse phenomenon occurs due to each variation is used for adjustment of the image forming condition, the adjustment cannot be appropriately performed, and thus is not adopted in processing. However, for this reason, the reading gradation pattern chart 100 may be wasted.

  Therefore, in the image forming unit 210, based on both the reading accuracy of the image reading unit 110 and the image forming accuracy of the density in the image forming unit 210, the high density side in the reading gradation pattern chart 100 is used. Each gradation pattern 101 is formed such that the reading value of the image reading unit 110 of the gradation pattern 101 is larger than the reading value of the image reading unit 110 in the gradation pattern 101 on the low density side. It is preferable.

  Specifically, for example, the variation in the reading accuracy of the image reading unit 110 and the variation in the image forming accuracy with respect to the density in the image forming unit 210 are appropriately generated as accuracy information, or the distribution of variation or the like is determined in advance as accuracy information. Is stored in the storage means. A dither value for forming the gradation pattern 101 is determined in advance based on the accuracy information so that the reading values of the image reading unit 110 corresponding to the different gradation patterns 101 are different. As a result, the reading value of the gradation pattern 101 in the reading gradation pattern chart 100 is not reversed, and the reading value can be suitably used for determining the γ characteristic.

  Thus, in the image processing method according to the present invention, the first step of forming the reading gradation pattern chart 100 having a plurality of kinds of gradation patterns 101 corresponding to different known dither values, and the reading The gradation pattern chart is read by the CCD 116, the second process of storing the relationship between the read value and the dither value, and the target read value of the input density obtained by reading the standard pattern chart by the CCD 116. And a third step for obtaining a relationship between the input density of the CCD 116 and the dither value based on the read reference value determined in this step and the read value stored in the second step. .

  Accordingly, the relationship between the input density obtained based on the reading reference value and the actual reading value and the dither value at the time of image formation is appropriately obtained. Therefore, even if the relationship of the reference γ characteristic is not stored in the storage means, the optimum γ characteristic can always be easily obtained.

  Further, in the image processing method, based on the relationship between the input density and the dither value determined in the third step, a fourth step for forming the visual gradation pattern chart 200, and the visual floor A fifth process in which the relationship is manually adjusted by visually observing the tone pattern chart 200, and a value corresponding to the target value obtained by the relationship adjusted in the fifth process is used as the reading reference value. 6 strokes.

  Thereby, the density of the visual gradation pattern chart determined by the visual observation of the user can be added to the image processing. Therefore, the γ characteristic can be determined easily and appropriately.

  In the above-described embodiment, the determination of the γ characteristic for the image forming apparatus in which the image reading unit and the image forming unit are integrally configured has been described. However, the image reading unit and the image forming unit are independent of each other. The present invention is also applicable to a case where an apparatus provided as a result, that is, a scanner apparatus having only a document image reading function and a printer apparatus having only a function of forming an image based on image data are connected and used on a network. Is possible. The present invention can also be applied to a case where the printer device is simply corrected by the scanner device.

  Further, the technique for suppressing the influence of the edge effect of the gradation pattern and the influence of toner replenishment followability can be applied not only to the reading gradation pattern chart but also to the visual gradation pattern chart. The application to the visual gradation pattern chart is to prevent the density between gradations from being recognized differently from the actual one when visually observed.

  The above-described image forming apparatus and image processing method may have the following configurations.

  That is, the above-described image forming apparatus is formed on the recording material with image forming means for forming an image on the recording material by forming an electrostatic latent image on the photoreceptor based on the first image information. When the image information input means for inputting the second image information based on the image and the image is a pattern chart in which different gradation patterns are arranged, the second image information is processed, and image processing conditions And an image processing unit for adjusting the electrostatic latent image of each gradation pattern adjacent to the image forming unit in the sub-scanning direction when the image forming unit forms the pattern chart. It can also be expressed as a configuration in which each gradation pattern is formed so as to avoid the enhancement of the electric field due to the difference in potential difference at the boundary portion.

  According to the above configuration, when correcting the gradation property to an appropriate one by forming a pattern chart and inputting the pattern chart to the image information input unit, the density difference between the gradation patterns adjacent in the sub-scanning direction is predetermined. A pattern chart smaller than the value is formed. For this reason, it is possible to avoid the nonuniformity of the density of the gradation pattern due to the occurrence of the edge effect and the toner replenishment followability, so that the overall density of each gradation pattern in the pattern chart becomes uniform. As a result, the gradation pattern can be read stably, so that the image forming conditions can be adjusted reliably and appropriately.

  In the image forming apparatus, it is preferable that the image forming unit forms a pattern chart so that each gradation pattern adjacent in the sub-scanning direction of the image forming unit is in direct contact.

  According to the above configuration, since no white display or black display boundary is provided between the gradation patterns, it is possible to prevent an edge effect from occurring between the gradation pattern and the boundary. Therefore, it is possible to further improve the input stability of the gradation pattern by making the overall density of the gradation pattern more uniform.

  In the image forming apparatus, the image forming unit may be adjacent to the gradation pattern serving as an end portion in the sub-scanning direction in the pattern chart and have the same density as or close to the gradation pattern serving as the end portion. It is preferable to form a dummy pattern.

  According to the above configuration, since the dummy pattern is formed at the end of the pattern chart in the sub-scanning direction, the density difference between the background of the recording material forming the pattern chart and the gradation pattern is reduced by the dummy pattern. be able to. As a result, it is possible to more reliably avoid the edge effect particularly in the gradation pattern at the end portion in the sub-scanning direction.

  In the image forming apparatus, the image forming unit further includes a plurality of gradation patterns having a gradation pattern that changes from a low density to a high density along the sub-scanning direction of the image forming means and has the closest density to each other. It is preferable to form a pattern chart so that are arranged in the main scanning direction.

  According to the above configuration, when the pattern chart is formed by the image forming unit, gradation patterns with higher density do not continue in the direction in which the pattern chart is developed. For this reason, it is possible to satisfactorily avoid the occurrence of non-uniformity in the density of the gradation pattern due to the toner replenishment followability at the time of pattern chart formation.

  Further, the image forming apparatus described above includes an image forming unit that forms an image on a recording material based on the first image information, and an image that reads the image formed on the recording material and forms second image information. In an image forming apparatus comprising: a reading unit; and an image processing unit that processes the second image information and adjusts an image processing condition when the image is a pattern chart in which different gradation patterns are arranged. The image processing means can also be expressed as a configuration that adjusts image processing conditions by performing image processing on the second image information on the basis of the background color of the recording material on which the pattern chart is formed. .

  According to the above configuration, image processing is performed in consideration of the background color of the recording material forming the pattern chart at the time of shading correction. Therefore, it becomes possible to make the input density of the gradation pattern to the background more appropriate, and as a result, the gradation pattern can be read stably, so that the image forming conditions can be adjusted reliably and appropriately. Can do.

  In the image forming apparatus, the image processing unit further reduces the amount of light applied to the pattern chart when the image reading unit reads the pattern chart, or reduces the reading gain of the image reading unit. It is preferable that the second image information is subjected to image processing based on the read value obtained in this way.

  According to the above configuration, the reading value of the pattern chart (gradation pattern) by the image reading unit is read so as to be smaller than the actual value. Therefore, at the time of shading correction, even when the whiteness of the reference white plate is lower than the whiteness of the background density of the pattern chart, the background density can be read by the image reading unit. As a result, even when the whiteness of the reference white plate is lower than the whiteness of the background density, the gradation pattern is stably read by making the input density of the gradation pattern to the background more appropriate. be able to.

  Further, the image forming apparatus described above includes an image forming unit that forms an image on a recording material based on the first image information, and an image that reads the image formed on the recording material and forms second image information. In an image forming apparatus comprising: a reading unit; and an image processing unit that processes the second image information and adjusts an image processing condition when the image is a pattern chart in which different gradation patterns are arranged. The first image information for forming the pattern chart is multi-gradation by adding a dither value by a dither matrix, and the image reading means has an image filter of the same size as the dither matrix. It can also be expressed as a configuration for reading the pattern chart via.

  According to the above configuration, since the pattern chart is read through the image filter having the same size as the dither matrix of the image information, interference occurs between the spatial frequency of the gradation pattern and the image reading means, and moire is generated. The problem of occurrence can be prevented without using mechanical means. Therefore, it is possible to easily improve the reading accuracy of the gradation pattern while avoiding the complexity of the apparatus.

  Further, the image forming apparatus described above includes an image forming unit that forms an image on a recording material based on the first image information, and an image that reads the image formed on the recording material and forms second image information. In an image forming apparatus comprising: a reading unit; and an image processing unit that processes the second image information and adjusts an image processing condition when the image is a pattern chart in which different gradation patterns are arranged. The image forming unit outputs the output of the image reading unit in the high density side gradation pattern in the pattern chart based on both the input accuracy of the image reading unit and the image forming accuracy of the density in the image forming unit. It is expressed that the pattern chart is formed so that the value is larger than the output value of the image reading means in the gradation pattern on the low density side. And it can also be.

  According to the above configuration, since the image is formed based on both the image forming accuracy in the density of the image forming unit and the input accuracy of the density of the image reading unit, variations occurring in the image forming accuracy and the input accuracy are caused. A pattern chart can be formed in consideration. As a result, it is possible to avoid the occurrence of a reversal phenomenon that is likely to occur in the pattern chart, and the gradation pattern that is originally on the higher density side becomes a value corresponding to the lower density side, thereby preventing unnecessary formation of the pattern chart. Thus, more accurate image forming conditions can be adjusted.

  Further, the image forming apparatus described above is formed on the recording material, and an image forming unit that forms an image on the recording material based on the first image information that has been multi-gradated by adding a dither value based on a dither matrix. The second image information is processed and the image processing conditions when the image reading means that reads the image that has been read into the second image information and the image is a pattern chart in which different gradation patterns are arranged In the image forming apparatus comprising the image processing unit for adjusting the image reading unit, the image processing unit includes a target reading value of the reading density of the image reading unit and the image reading unit that is determined corresponding to the target reading value. Based on the relationship between the reading reference value and the relationship between the actual reading value obtained by reading the pattern chart by the image reading unit and the dither value, the image It is configured to implement an image processing for obtaining the relationship between the input density and the dither value of the formation means, and can be expressed.

  Further, in the image processing method used in the image forming apparatus that forms an image by the image forming unit based on the image information, the above-described image processing method is a pattern for reading a plurality of types of gradation patterns corresponding to different known dither values. As a chart, a first step of forming the chart on the recording material by the image forming means and the reading pattern chart by the image reading means are directly read and inputted, and the relationship between the input value and the dither value is stored. The input density of the image forming unit based on the second step, the reading reference value determined corresponding to the input density target value of the image reading unit, and the reading value stored in the second step, It can also be expressed as a method including a third step for obtaining the relationship with the dither value.

  According to the above configuration or method, the relationship between the input density obtained based on the reading reference value and the actual reading value and the dither value at the time of image formation is determined as appropriate. Therefore, even if the relationship of the reference γ characteristic is not stored in the storage means, it is only necessary to have a correspondence table between the target input value of the concentration of the γ characteristic and the input reference value, which requires only a small memory capacity. The optimum γ characteristic can always be easily obtained.

  In the image processing method, the fourth step of forming a visual pattern chart on the recording material based on the relationship between the input density and the dither value determined in the third step, and the visual processing A fifth process in which the relationship is manually adjusted by visually observing the pattern chart, and a value corresponding to the target value obtained by the relationship adjusted in the fifth process is used as the reading reference value. It is preferable to have this process.

  According to the above method, not only the reading pattern chart but also the density of the visual pattern chart determined by the user's visual observation can be added to the image processing. Therefore, the γ characteristic can be determined easily and appropriately.

  In the processing method, any one of the reading reference value obtained in the sixth step and the reading reference value determined corresponding to the target input value of the input density in the third step is further provided. Is preferably used as the reading reference value for the third stroke.

  According to the above method, there are two types of standard reading reference values (values determined in the third step) and reading reference values taking into account user preferences (values obtained in the sixth step). The reading reference value is properly used. Therefore, for example, when the image forming apparatus is shipped from the factory, it is not necessary to consider the user's preference. Therefore, the standard reading reference value is used, and the apparatus is installed at the user's hand. In this case, set the reading reference value taking into account the user's preference. Furthermore, when the user moves the device, the original standard reading reference value is used. The reading reference value can be made appropriate depending on the situation. As a result, the setting can be simplified.

  Further, the above-described image processing method can be used to form a first image on a recording material based on the first image information, and on the recording material based on information obtained by reading the first image by an image reading unit. In the image processing method of adjusting image processing conditions by inputting information obtained visually from the second image by manual input means after forming the second image on the first image, the gradation of the first image It can also be expressed that the number is larger than the number of gradations of the second image.

  In general, when the gradation is determined by the image reading unit, it is possible to determine the gradation more accurately when the number of gradations is larger. However, when the user visually determines the gradation, If the number of gradations is too large, the determination becomes complicated and accurate gradation determination cannot be performed. On the contrary, if the number of gradations is small, it is suitable for the user's determination, but the image reading means cannot make an accurate determination. On the other hand, according to the above method, since the number of gradations of the first image is larger than the number of gradations of the second image, more accurate gradation determination can be realized. .

  That is, according to the above method, since the number of gradations of the first image is larger than the number of gradations of the second image, it is possible to achieve more accurate determination of gradation and use When the person visually adjusts the image forming conditions, it is possible to avoid a situation in which the gradation is increased or the visual discrimination is difficult due to the adjacent gradation.

  With the above-described configuration, in the image forming apparatus that corrects the gradation property by forming a gradation pattern and causing the image reading unit to read the gradation pattern, which is the object of the present invention, the edge effect and the toner An image forming apparatus that can adjust the image forming conditions surely and appropriately by forming a gradation pattern chart in consideration of replenishment followability and thereby making the gradation pattern reading density more appropriate. Can be provided.

  In addition, with the above-described configuration, when the gradation pattern, which is another object of the present invention, is read, the reading density of the gradation pattern is reduced by correcting the background of the paper on which the gradation pattern is formed. By making it more appropriate, it is possible to provide an image forming apparatus that can adjust the image forming conditions reliably and appropriately.

  Further, with the above-described configuration, when reading the gradation pattern, which is another object of the present invention, the reading accuracy of the gradation pattern can be easily increased without complicating the apparatus configuration using mechanical means. An image forming apparatus that can be improved can be provided.

  In addition, with the above-described configuration, it is possible to easily and appropriately determine the γ characteristic by reading the gradation pattern and obtaining the relationship between the input density and the dither value, which is another object of the present invention. An image forming apparatus and an image processing method used therefor can be provided.

  Further, there is known a conventional technique (the above-described techniques (1) and (7)) in which a gradation pattern is simply read to correct a reference γ characteristic curve. Here, regarding the gradation correction of the image, a visual gradation pattern chart may be used in addition to the reading gradation pattern chart for reading by the image reading unit. This visual gradation pattern chart is for preventing the density between gradations from being recognized differently from the actual one when visually observed. However, each of the above conventional techniques does not mention how to set the number of reading gradation patterns and the number of visual gradation patterns.

  The image forming apparatus according to the present invention can be applied to a digital color copying machine including a color image reading unit and a color image forming unit.

FIG. 5 is an explanatory diagram showing the order of density of each gradation pattern in a reading gradation pattern chart used in the image forming apparatus according to the embodiment of the present invention. It is a schematic sectional drawing which shows the structure of the image forming apparatus concerning this invention using the gradation pattern chart shown in FIG. FIG. 3 is a block diagram illustrating a configuration of an image processing unit in the image forming apparatus illustrated in FIG. 2. FIG. 3 is a block diagram illustrating a configuration of a control system in the image forming apparatus illustrated in FIG. 2. FIG. 3 is a plan view illustrating a configuration of an operation panel provided in the image forming apparatus illustrated in FIG. 2. FIG. 6 is an explanatory diagram showing a standby screen displayed when the color LCD is on standby in the operation panel shown in FIG. 5. FIG. 6 is an explanatory diagram illustrating an example of a selection screen displayed when the color LCD is on standby in the operation panel illustrated in FIG. 5. FIG. 6 is an explanatory diagram showing an operation initial setting screen displayed when initializing an operation of a color LCD on the operation panel shown in FIG. 5. 3 is a flowchart showing an operation procedure by an operation panel in the image forming apparatus shown in FIG. 10 is a flowchart showing a continuation of the flowchart of FIG. 9. FIG. 6 is an explanatory diagram showing another example of a selection screen displayed when the color LCD is on standby in the operation panel shown in FIG. 5. FIG. 6 is an explanatory diagram showing another example of a selection screen displayed when the color LCD is on standby in the operation panel shown in FIG. 5. FIG. 6 is an explanatory diagram showing another example of a selection screen displayed when the color LCD is on standby in the operation panel shown in FIG. 5. FIG. 3 is a flowchart showing an operation procedure of γ characteristic setting processing in the image forming apparatus shown in FIG. 2. FIG. It is a flowchart which shows the continuation of the flowchart shown in FIG. FIG. 6 is an explanatory diagram showing a γ characteristic setting initial screen displayed when setting the γ characteristic of the color LCD on the operation panel shown in FIG. 5. FIG. 3 is an explanatory diagram showing a formation state of a toner patch in a high density region used for adjustment of an image forming station in the image forming apparatus shown in FIG. 2. It is explanatory drawing which shows the outline | summary of the gradation pattern chart for reading shown in FIG. FIG. 6 is an explanatory diagram showing a γ characteristic setting initial screen displayed when setting the γ characteristic of the color LCD on the operation panel shown in FIG. 5. FIG. 3 is an explanatory diagram showing an outline of a visual gradation pattern chart used for manual adjustment of the γ characteristic of the image forming apparatus shown in FIG. 2. FIG. 6 is an explanatory diagram showing a γ characteristic setting initial screen displayed when setting the γ characteristic of the color LCD on the operation panel shown in FIG. 5. FIG. 6 is an explanatory diagram showing a screen during automatic calculation of γ characteristics displayed when setting γ characteristics of a color LCD on the operation panel shown in FIG. 5. FIG. 6 is an explanatory diagram showing a screen during manual adjustment of the γ characteristic displayed when setting the γ characteristic of the color LCD on the operation panel shown in FIG. 5. It is a flowchart which shows the control procedure of the up / down key operation possible / impossible display switching treatment in the flowchart shown in FIG. FIG. 6 is an explanatory diagram showing a screen during manual adjustment of the γ characteristic displayed when setting the γ characteristic of the color LCD on the operation panel shown in FIG. 5. FIG. 6 is an explanatory diagram showing a screen during manual adjustment of the γ characteristic displayed when setting the γ characteristic of the color LCD on the operation panel shown in FIG. 5. FIG. 6 is an explanatory diagram showing a screen during manual adjustment of the γ characteristic displayed when setting the γ characteristic of the color LCD on the operation panel shown in FIG. 5. FIG. 28 is an explanatory diagram showing an example of the range of the upper limit value and the lower limit value of the adjustment point when setting the γ characteristic of the color LCD in the operation panel shown in FIGS. 25 to 27. FIG. 3 is an explanatory diagram illustrating problems during reading of a reading gradation pattern chart in the image forming apparatus illustrated in FIG. 2. FIG. 30 is an explanatory diagram showing a rotation direction of the photosensitive drum for explaining a reading direction of the reading gradation pattern chart shown in FIG. 29. FIG. 5 is an explanatory diagram showing another problem when reading the reading gradation pattern chart in the image forming apparatus shown in FIG. 2. It is explanatory drawing which shows the other example of the gradation pattern chart for a reading shown in FIG. It is explanatory drawing which shows the further another example of the gradation pattern chart for reading shown in FIG. It is explanatory drawing which shows the further another example of the gradation pattern chart for reading shown in FIG. FIG. 2 is an explanatory diagram showing an outline of density distribution of individual gradation patterns in the reading gradation pattern chart shown in FIG. 1. (A) is explanatory drawing which shows the correspondence of 1 pixel which CCD which the image forming apparatus shown in FIG. 2 comprises reads, and 1 dot of a dither matrix, (b) is the gradation pattern for reading shown in FIG. It is explanatory drawing which shows the relationship between 1 pixel at the time of reading a chart with CCD, and each gradation pattern. FIG. 3 is an explanatory diagram illustrating an example of correcting whiteness of a background of the reading gradation pattern chart when the CCD included in the image forming apparatus shown in FIG. 2 reads the reading gradation pattern chart shown in FIG. 1; 3 is a graph showing a relationship between a read value of a gradation pattern and a dither value of the gradation pattern in the image forming apparatus shown in FIG. 39 is a graph showing the relationship between the dither value and the CCD output value obtained from the relationship between the read value of the gradation pattern and the dither value of the gradation pattern and the relationship between the target read value and the CCD output value shown in FIG. . FIG. 3 is an explanatory diagram illustrating a relationship between a ground output level and a gradation pattern output level when the CCD included in the image forming apparatus illustrated in FIG. 2 reads the reading gradation pattern chart illustrated in FIG. 1.

Explanation of symbols

2 Image processing unit (image processing means)
100 gradation pattern chart for reading (pattern chart, first image)
101 gradation pattern 110 image reading unit (image reading means / image information input means)
131 Dummy pattern 200 Visual gradation pattern chart (pattern chart / second image)
210 Image forming unit (image forming means)
222a to 222d Photosensitive drum (photosensitive member)
624 execution key (manual input means / image information input means)
663a Density up key (manual input means / image information input means)
663b Density down key (manual input means / image information input means)
664a Adjustment point up key (manual input means / image information input means)
664b Adjustment point down key (manual input means / image information input means)

Claims (11)

Image forming means for forming and outputting a pattern chart in which different gradation patterns are arranged on a recording material by forming an electrostatic latent image on a photoconductor based on first image information;
Image processing means for adjusting the image processing conditions by processing the second image information input based on the pattern chart output from the image forming means,
In the image forming apparatus capable of outputting a reading pattern chart that causes the image processing means to input the second image information by being read by an image reading means that reads an original image.
The image forming means includes
As a pattern chart for inputting the second image information to the image processing means, a visual pattern that allows the image processing means to input the second image information in response to a user request when used by the user. A chart can be output,
When forming at least one of the reading pattern chart and the visual pattern chart, the electric field due to the difference in potential difference at the boundary portion of the electrostatic latent image of each gradation pattern adjacent in the sub-scanning direction on the photoconductor. In order to reduce the density difference between the adjacent areas in the sub-scanning direction so as to avoid emphasis, the gradation pattern is changed from the low density to the high density along the sub-scanning direction on the photoconductor, and the density is the highest in each other. The gradation patterns are arranged in two rows in the sub-scanning direction so that two gradation patterns close to each other are arranged in the main scanning direction, and the gradation patterns adjacent to each other in the sub-scanning direction on the photosensitive member are brought into direct contact with each other. An image forming apparatus.   When the image processing means inputs the second image information using the reading pattern chart, the second image information is based on the background color of the recording material on which the reading pattern chart is formed. The image forming apparatus according to claim 1, wherein image processing conditions are adjusted to adjust image processing conditions.   The image processing means can be obtained by reducing the amount of light applied to the reading pattern chart or reducing the reading gain of the image reading means when the reading pattern chart is read by the image reading means. The image forming apparatus according to claim 2, wherein the second image information is subjected to image processing based on the read value. The first image information for forming the reading pattern chart is multi-gradation by adding a dither value by a dither matrix,
The image forming apparatus according to claim 1, wherein the image reading unit reads the reading pattern chart through an image filter having the same size as the dither matrix.   The image forming means is based on both the input accuracy of the image reading means and the image forming accuracy of the density in the image forming means, and the image reading means in the gradation pattern on the high density side in the reading pattern chart. 2. The image forming apparatus according to claim 1, wherein the reading pattern chart is formed so that an output value is larger than an output value of the image reading unit in a gradation pattern on a low density side. The first image information for forming the reading pattern chart is multi-gradation by adding a dither value by a dither matrix,
The image processing means includes the relationship between the target reading value of the reading density of the image reading means and the reading reference value of the image reading means determined corresponding to the target reading value, and the reading pattern chart. Image processing for obtaining a relationship between the input density of the image forming unit and the dither value based on the relationship between the actual reading value obtained by reading by the image reading unit and the dither value is performed. The image forming apparatus according to claim 1. In an image processing method of forming a pattern chart in which different gradation patterns are arranged on a recording material based on image information, and adjusting image forming conditions of an image forming apparatus having a photoconductor using the pattern chart,
Outputting a reading pattern chart for adjusting image forming conditions by being read by an image reading means for reading a document image;
And a step of outputting a visual pattern chart for adjusting image forming conditions according to the user's request by using the user ,
When forming at least one of the reading pattern chart and the visual pattern chart, the electric field due to the difference in potential difference at the boundary portion of the electrostatic latent image of each gradation pattern adjacent in the sub-scanning direction on the photoconductor. In order to reduce the density difference between the adjacent areas in the sub-scanning direction so as to avoid emphasis, the gradation pattern is changed from the low density to the high density along the sub-scanning direction on the photoconductor, and the density is the highest in each other. The gradation patterns are arranged in two rows in the sub-scanning direction so that two gradation patterns close to each other are arranged in the main scanning direction, and the gradation patterns adjacent to each other in the sub-scanning direction on the photosensitive member are brought into direct contact with each other. An image processing method characterized by the above. A first step of forming a plurality of types of gradation patterns corresponding to known different dither values on the recording material by the image forming means as the reading pattern chart;
A second step of directly reading and inputting the reading pattern chart by the image reading means, and storing the relationship between the input value and the dither value;
Based on the reading reference value determined corresponding to the target value of the input density of the image reading unit and the reading value stored in the second step, the input density of the image forming unit and the dither value are The image processing method according to claim 7, further comprising a third step of obtaining a relationship. A fourth step of forming the visual pattern chart on the recording material based on the relationship between the input density and the dither value determined in the third step;
A fifth step of manually adjusting the relationship by visually observing the visual pattern chart;
9. The image processing method according to claim 8, further comprising: a sixth step in which a value corresponding to the target value obtained by the relationship adjusted in the fifth step is used as the reading reference value.   One of the reading reference value obtained in the sixth step and the reading reference value determined corresponding to the target input value of the input density in the third step is used as the third step. The image processing method according to claim 9, wherein the image processing method is used as a reading reference value.   11. The image processing method according to claim 7, wherein the number of gradations of the reading pattern chart is larger than the number of gradations of the visual pattern chart.

Images