JP6572579B2 - Image processing apparatus, image forming apparatus, image forming system, and image processing method - Google Patents

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, and an image forming system capable of eliminating density unevenness in a specific direction that can occur in an image forming apparatus without using a dedicated chart or an image area having a specific density. And an image processing method.

  As an image forming apparatus, an image of a photosensitive drum or the like in a state in which exposure for each line or a plurality of lines in the first direction (main scanning direction) according to image data is driven in the second direction (sub-scanning direction). It is known that two-dimensional (every page) image formation is performed by repeatedly performing on a carrier.

  As an example, in an electrophotographic image forming apparatus, a light beam modulated in accordance with image data is scanned in the main scanning direction on the surface of a charged photosensitive drum, and in parallel with this, the photosensitive drum is It is driven to rotate in the sub-scanning direction. Then, the electrostatic latent image formed on the photosensitive drum is developed by a developing device to be converted into a toner image, and the toner image is transferred onto a sheet.

  In such an image forming apparatus, uneven charging voltage on the surface of the photosensitive drum, inclination of the photosensitive drum, unevenness of the fixing device that fixes the toner image on the paper, characteristics of the optical system that scans the light beam in the main scanning direction, etc. It is known that density unevenness occurs in the main scanning direction due to various factors. This uneven density often occurs as a decrease in image density at the end portion in the main scanning direction as compared to the central portion in the main scanning direction.

  As for the method for eliminating the density unevenness in the main scanning direction of the image forming apparatus as described above, a method for performing correction by reading the image with a scanner after forming a dedicated test chart arranged in the main scanning direction, There are various methods such as those described in the following patent documents.

JP 2005-153165 A

In order to eliminate the density unevenness in the main scanning direction at the time of image formation as described above, a method using a test chart is executed as follows.
First, a test chart having a belt-like patch image in the main scanning direction is printed. The paper on which the test chart is printed is read by a scanner to detect density unevenness. Then, correction data capable of eliminating the detected density unevenness is calculated, and the correction data is applied to the image data in the image processing unit in the image forming apparatus. By doing so, it is possible to eliminate density unevenness in the main scanning direction.

  However, in this case, it is necessary to print the test chart as described above before obtaining the correction data. That is, normal image formation is limited by the time for outputting the test chart, and productivity is lowered. There is also a problem of consuming paper and toner.

In addition, when the normal image formation schedule is clogged, there is a new problem that density unevenness cannot be corrected because time for outputting a test chart cannot be taken.
On the other hand, in Patent Document 1 described above, it is proposed to perform density unevenness detection and correction similar to those in the above test chart using a constant density area included in a graphic image in an image to be formed.

In this case, it is assumed that there is a region having a constant density continuously in the main scanning direction in the image. For this reason, there is a problem that density unevenness cannot be detected and corrected unless there is a continuous area in the main scanning direction with a constant density.
The present invention has been made in view of such problems, and does not obstruct the normal operation of the image forming apparatus by printing a dedicated test chart, and does not require the presence of a constant density area in the image. It is an object of the present invention to realize an image processing apparatus, an image forming apparatus, an image forming system, and an image processing method capable of detecting and correcting density unevenness occurring in formation.

One embodiment of the present invention for solving the above-described problems is as follows.
(1) An image processing apparatus that reflects one aspect of the present invention repeatedly executes linear image formation in a first direction in a second direction orthogonal to the first direction to form a two-dimensional image on a recording medium. An image processing apparatus used for image processing in an image forming apparatus that performs formation, the image data before output used for image formation by the image forming apparatus, and an image formed on the recording medium by the image forming apparatus An input / output gradation characteristic calculating unit that calculates an input / output gradation characteristic indicating a correspondence relationship between densities of the same pixel with respect to post-output image data obtained by scanning the image data for each of a plurality of different areas in the first direction; A correction data calculation unit that calculates correction data for each of a plurality of areas to eliminate a difference between the input / output gradation characteristics for each of the plurality of areas and a reference input / output gradation characteristic; and the correction for each of the plurality of areas According to the data Has an image processing section performing image processing to correct the force before the image data to eliminate the difference between the input-output gradation characteristics of different each of the plurality of regions in the first direction, wherein the input-output gray level characteristic FIG. 5 shows a correspondence relationship between the density of the plurality of pre-output images in a region and the density of the post-output image data of the same pixel for each density of the pre-output image.

  An image forming apparatus reflecting one aspect of the present invention includes the above image processing apparatus, an image forming unit that forms an image based on pre-output image data that has been subjected to image processing by the image processing apparatus, and the image forming apparatus. An image reading unit that reads the image formed by the unit and generates the post-output image data.

  An image forming system reflecting one aspect of the present invention includes the above image processing apparatus, an image forming apparatus that forms an image based on pre-output image data that has been subjected to image processing by the image processing apparatus, and the image forming apparatus. An image reading device that reads the image formed by the device and generates the post-output image data.

Also, an image processing method reflecting one aspect of the present invention is a two-dimensional image formation on a recording medium by repeatedly performing linear image formation in the first direction in a second direction orthogonal to the first direction. An image processing method for an image processing apparatus used for image processing in an image forming apparatus for executing image processing, comprising: pre-output image data used for image formation by the image forming apparatus; and formed on the recording medium by the image forming apparatus An input / output gradation characteristic indicating a correspondence relationship of the density of the same pixel with respect to post-output image data obtained by scanning the obtained image is calculated for each of a plurality of different areas in the first direction, and Correction data that eliminates the difference between the input / output gradation characteristics and the reference input / output gradation characteristics is calculated for each of a plurality of areas, and the pre-output image data is corrected using the correction data for each of the plurality of areas. Said It is intended to image processing so as to eliminate the difference between the input-output gradation characteristics of each of a plurality of regions different in one direction, the input-output gradation characteristics, and concentration of a plurality of said output pre-image area, wherein It shows the correspondence between the density of the pre-output image and the density of the post-output image data of the same pixel.

(2) In the above (1), the input / output gradation characteristic calculation unit calculates the reference input / output gradation characteristic based on an average of the input / output gradation characteristics for each of a plurality of regions.
(3) In the above (1), the input / output gradation characteristic calculation unit uses an input / output gradation characteristic given in advance as the reference input / output gradation characteristic.

  (4) In the above (1), the input / output gradation characteristic calculation unit, when a necessary amount of the pre-output image data and the post-output image data is obtained, outputs the input / output floor for each of a plurality of areas. The reference input / output gradation characteristics are calculated based on the average of the gradation characteristics, and when the necessary amount of the pre-output image data and the post-output image data is not obtained, the input / output gradation characteristics given in advance are calculated. Used as the reference input / output gradation characteristics.

  (5) In the above (1) to (4), the input / output gradation characteristic calculation unit can obtain the pre-output image data and the post-output image data only in a partial region or a partial gradation. The input / output gradation characteristics are calculated only for the partial area or the partial gradation, and the correction data calculation unit The correction data is generated for some gradations.

(6) In the above (1) to (5), when the image forming apparatus forms a color image on the recording medium using a plurality of color materials, the input / output gradation characteristic calculating unit The input / output gradation characteristics are calculated for pixels that use only one of the color materials.
(7) In the above (1) to (6), when the input / output gradation characteristic calculation unit calculates the input / output gradation characteristic in a plurality of regions different in the first direction, the first direction The correction data calculation unit calculates the correction data for each region in accordance with the region setting change in the input / output gradation characteristic calculation unit.

  (8) In the above (1) to (7), the input / output gradation characteristic calculation unit is configured to determine the first direction as a plurality of regions different in the first direction when calculating the input / output gradation characteristic. It is assumed that the area is roughly divided near the center and the area is finely divided near the end in the first direction.

According to the image processing apparatus, the image forming apparatus, the image forming system, and the image processing method reflecting one aspect of the present invention, the following effects can be obtained.
(1) In the image processing apparatus, the image forming apparatus, the image forming system, and the image processing method reflecting one aspect of the present invention, linear image formation in the first direction is repeated in the second direction orthogonal to the first direction. When executing two-dimensional image formation on the recording medium, input / output gradation characteristics of the pre-output image data and post-output image data are calculated for each of a plurality of different areas in the first direction, and The correction data for eliminating the difference between the input / output gradation characteristics for each area and the reference input / output gradation characteristics is calculated for each of the plurality of areas, and the pre-output image data is corrected by the correction data for each of the plurality of areas. Image processing is as follows.

For this reason, it is possible to detect and correct density unevenness occurring in image formation without requiring the printing of a dedicated test chart or the presence of a constant density region in the image.
Accordingly, it is possible to avoid a situation in which normal image formation is restricted by the print of the test chart and productivity is lowered. In addition, the problem of consuming paper, toner, and the like is solved. Furthermore, even when the normal image formation schedule is clogged, a test chart is not necessary, so that density unevenness can be corrected at an arbitrary timing.

(2) In the above (1), by calculating the reference input / output gradation characteristics by the average of the input / output gradation characteristics for each of the plurality of areas, the density unevenness of each of the plurality of areas can be reduced with a small correction amount. It becomes possible to correct.
(3) In the above (1), the input / output gradation characteristics given in advance are used as the reference input / output gradation characteristics, and the input of pre-output image data and post-output image data is sufficient. Even when there is no accumulation, it becomes possible to ensure the reference input / output gradation characteristics. In addition, it is possible to correct density unevenness based on predetermined input / output gradation characteristics for each of a plurality of regions.

  (4) In the above (1), when the required amount of pre-output image data and post-output image data is obtained, the input / output gradation characteristics serving as a reference are obtained by averaging the input / output gradation characteristics for each of a plurality of areas. By calculating the above, it is possible to correct the density unevenness of each of the plurality of regions with a small correction amount.

  In addition, when the required amount of pre-output image data and post-output image data is not obtained, the input / output gradation characteristics given in advance are used as reference input / output gradation characteristics, so It becomes possible to correct the density unevenness based on the input / output gradation characteristics of the predetermined region.

  (5) In the above (1) to (4), when the pre-output image data and the post-output image data are obtained only in a partial area or a partial gradation, the partial area or The input / output gradation characteristics are calculated using only the partial gradation, and correction data is generated in a partial region or a partial gradation where the input / output gradation characteristics exist. In this way, even when there are few inputs of pre-output image data and post-output image data and a complete input / output gradation characteristic cannot be generated, density unevenness can be corrected in each of a plurality of regions. It becomes possible. In addition, when the pre-output image data and the post-output image data are obtained in only a part of the area or a part of the gradation, the part of the area or the part of the gradation is only an area necessary for the correction. Or since it is a gradation, a problem does not arise.

  (6) In the above (1) to (5), when the image forming apparatus forms a color image on a recording medium using a plurality of color materials, only one color material is used. By calculating the input / output gradation characteristics in the pixel, it is possible to accurately determine and correct the input / output gradation characteristics caused by uneven density of the target color without being affected by the color material of other colors. become.

  (7) In the above (1) to (6), when calculating input / output gradation characteristics in a plurality of regions different in the first direction, the setting of the plurality of regions in the first direction can be changed. By calculating correction data for each area according to the area setting change in the output tone characteristic calculation unit, depending on the presence or absence of density unevenness, and depending on the required density unevenness accuracy In addition, it is possible to calculate and correct an appropriate density unevenness according to an allowable calculation amount.

  (8) In the above (1) to (7), as a plurality of regions different in the first direction when calculating the input / output gradation characteristics, a region roughly divided near the center in the first direction, the first direction By making the area finely divided in the vicinity of the edge, it is possible to calculate and correct appropriate density unevenness accurately and with a minimum amount of calculation at the edge where density unevenness easily occurs. .

1 is a block diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment of the present invention. 1 is a configuration diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment of the present invention. It is a block diagram which shows the structure of the image processing apparatus of embodiment of this invention. 6 is a flowchart illustrating an image forming operation according to the embodiment of the present invention. It is explanatory drawing which shows the mode of the image processed by embodiment of this invention with a photographic image. It is explanatory drawing which shows the mode of the image processed by embodiment of this invention with a photographic image. It is a characteristic view which shows the characteristic of the image processing in embodiment of this invention. It is a characteristic view which shows the characteristic of the image processing in embodiment of this invention. It is a characteristic view which shows the characteristic of the image processing in embodiment of this invention. It is a characteristic view which shows the characteristic of the image processing in embodiment of this invention. It is a characteristic view which shows the characteristic of the image processing in embodiment of this invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.
Here, the embodiment will be described in detail with a focus on the image forming apparatus 100 including the image processing apparatus.

〔overall structure〕
First, the configuration of the image forming system 1 or the image forming apparatus 100 according to the present embodiment will be described with reference to FIGS.
The image forming apparatus 100 includes a control unit 101, a communication unit 102, an operation display unit 103, a storage unit 104, a paper feeding unit 105, a conveyance unit 107, a document reading unit 110, and a density unevenness detection unit 120. The image data storage unit 130, the image processing unit 140, the image forming unit 150, the fixing unit 160, and the output product reading unit 190 are configured.

The image forming apparatus 100 repeatedly executes linear image formation in the first direction (main scanning direction) in a second direction (sub-scanning direction) orthogonal to the first direction to form a two-dimensional image on the recording medium. The image formation is executed.
Here, the control unit 101 controls each unit in the image forming apparatus 100 and also controls the entire image forming system. The communication unit 102 communicates with other connected devices. The operation display unit 103 notifies the control unit 101 of an operation input signal corresponding to the operation input by the operator, and also displays the status of the image forming apparatus 100, notifications, and warnings. The storage unit 104 stores a control program and various setting data, and is used as a work area for the control program. The paper feeding unit 105 feeds the stored paper toward the image forming unit 150. The transport unit 107 transports paper that has been fed and formed an image at a predetermined speed. The document reading unit 110 scans a document and generates image data. The density unevenness detection unit 120 detects density unevenness that occurs in the main scanning direction of the image formed on the paper and calculates correction data thereof. The image data storage unit 130 stores image data and various data used when forming an image. The image processing unit 140 executes various image processes necessary for image formation. The image forming unit 150 (see FIG. 2) executes printing (hereinafter referred to as “image formation”) by electrophotographic image formation / transfer / fixing based on an image formation command and image data after image processing. To do. The fixing unit 160 stabilizes the image transferred onto the paper by heat and pressure. The output material reading unit 190 reads an image of a sheet on which an image has been formed.

Further, as shown in FIG. 3, the image processing apparatus 1000 can be configured by the density unevenness detection unit 120 and the image processing unit 150. The image processing apparatus 1000 may exist in the image forming apparatus 100 or may exist as a single apparatus.
Here, the internal configuration of the image processing apparatus 1000 is shown in FIG. Here, the image processing apparatus 1000 includes a density unevenness detection unit 120 and an image processing unit 140.

In addition, the density unevenness detection unit 120 includes an input / output tone characteristic calculation unit 121, a reference tone characteristic holding unit 122, and a correction data calculation unit 123.
In this embodiment, image data used for image formation is referred to as “pre-output image data”. Also, image data generated as a result of reading an image of an image-formed sheet (post-output image) by the original reading unit 110 or the output product reading unit 190 is referred to as “post-output image data”. To do.

FIG. 5 schematically shows a state in which an image having no density unevenness (pre-output image) to be formed by pre-output image data is divided into five regions (AREA_1 to AREA_5) in the main scanning direction. Here, the white broken line schematically shows the division of the region.
FIG. 6 schematically shows a state in which an image formed by image data before output and having density unevenness in the main scanning direction (post-output image) is divided into five regions (AREA_1 to AREA_5) in the main scanning direction. Show. Here, the white broken line schematically shows the division of the region.

5 and 6 show specific examples in which the area is equally divided into five areas in the main scanning direction, but the present invention is not limited to this.
That is, it is possible to set a plurality of different areas in the main scanning direction. For example, in order to accurately detect density unevenness in the main scanning direction, it is possible to set more regions, for example, 10 regions in the main scanning direction.

Further, since uneven density hardly occurs near the center in the main scanning direction, a coarsely divided area is set. In the vicinity of an end in the main scanning direction, the density unevenness greatly changes, so that a finely divided area is set. It is also possible.
Such setting and setting change can be performed by various methods such as setting at the factory at the time of manufacture and setting by the user via the operation display unit 103 of the image forming apparatus 100. As will be described later, it is also possible to automatically set the number of areas from the result of calculating the input / output gradation characteristics.

  Here, the input / output gradation characteristic calculation unit 121 has the same pixel density for the pre-output image data used for image formation and the post-output image data obtained by scanning the image formed image. Input / output gradation characteristics indicating the correspondence relationship are calculated for each of a plurality of different regions in the first direction.

  That is, the input / output gradation characteristic calculation unit 121 determines the input / output gradation characteristics in the area AREA_1 in FIG. 5 and the area AREA_1 in FIG. 6 according to the density of the pre-output image data and the post-output image data in the same pixel. Is generated. Similarly, the input / output gradation characteristic calculation unit 121 includes the area AREA_2 in FIG. 5 and the area AREA_2 in FIG. 6, the area AREA_3 in FIG. 5 and the area AREA_3 in FIG. 6, the area AREA_4 in FIG. In the area AREA_4, the input / output gradation characteristics are generated by the density of the pre-output image data and the density of the post-output image data of the same pixel in the area AREA_5 in FIG. 5 and the area AREA_5 in FIG.

  In the case where the image forming unit 150 forms a color image on a recording medium using a plurality of color materials, the input / output tone characteristic calculation unit 121 uses only one of the color materials. The above input / output gradation characteristics are calculated in FIG. This makes it possible to accurately obtain the density unevenness of the target color without being affected by the color materials of other colors.

  When the pre-output image data and post-output image data necessary for calculating the input / output gradation characteristics are sufficiently obtained, the input / output gradation characteristic calculation unit 121 inputs / output gradation characteristics for each of a plurality of areas. Based on the average of the tone characteristics, the reference input / output tone characteristics are calculated. The reference input / output gradation characteristics are held in the reference gradation characteristic holding unit 122.

  Further, the input / output gradation characteristic calculation unit 121, when the pre-output image data and the post-output image data necessary for calculating the input / output gradation characteristic are not sufficiently obtained, is input in advance. The output gradation characteristics or the input / output gradation characteristics in the region near the center in the main scanning direction is held in the reference gradation characteristic holding unit 122 as the reference input / output gradation characteristics. Here, when the pre-output image data and post-output image data necessary for calculating the input / output gradation characteristics are not sufficiently obtained, the data on the graph is connected to obtain the minimum density. This means that a characteristic curve up to the maximum concentration can be generated.

The correction data calculation unit 123 calculates, for each of the plurality of areas, correction data that eliminates the difference between the input / output gradation characteristics for each of the plurality of areas and the reference input / output gradation characteristics, and sends the correction data to the image processing unit 140. Notice. The correction data will be described in detail later.
The image processing unit 140 corrects the pre-output image data with the correction data for each of the plurality of areas, and performs image processing so as to eliminate the difference in input / output gradation characteristics for each of the plurality of areas that differ in the first direction. That is, the image processing unit 140 performs image processing based on the correction data so that the input / output gradation characteristics match in a plurality of regions. As a result, density unevenness is eliminated by such image processing.

  1 and 2 show the image forming apparatus 100, the present invention is not limited to this. For example, it is possible to provide an image forming system in which the output product reading unit 190 is provided in the post-processing apparatus or another apparatus. In addition, an image forming system in which the image processing apparatus 1000 and the image forming apparatus 100 are configured separately can be used.

[Operation of Embodiment]
Hereinafter, the operation of this embodiment will be described with reference to the flowchart of FIG. 4 and characteristic diagrams showing specific examples of input / output gradation characteristics shown in FIG. Here, the operation will be described assuming that the image forming apparatus 100 includes the image processing apparatus 1000.

In the image forming apparatus 100, when the print processing operation starts, the control unit 101 performs initial setting of each unit (step S101 in FIG. 4).
When an image formation instruction and document image data are given (step S102 in FIG. 4), the control unit 101 stores document image data in the image data storage unit 130 as necessary, and an image processing unit as necessary. Image processing is executed at 140 (step S103 in FIG. 4).

If correction data (described later in step S103 in FIG. 4) has already been generated at the time of this image processing, image processing using the correction data is also executed.
The control unit 101 causes the image forming unit 150 to perform image formation using the image data that has been subjected to image processing by the image processing unit 140 (step S104 in FIG. 4).

  Here, if the output reading unit 190 exists in the image forming apparatus 100 and the setting is such that automatic reading is performed (YES in step S105 in FIG. 4), the sheet on which the image is formed by the image forming unit 150 The control unit 101 controls the output product reading unit 190 to read the image (post-output image) (step S106 in FIG. 4). The control unit 101 controls the image data (post-output image data) obtained by the output material reading unit 190 to be stored in the image data storage unit 130 in association with the pre-output image data described above (FIG. 4 in step S204).

  Further, even in an image forming system in which a reading device equivalent to the output object reading unit 190 is arranged as a post-processing device, image data (post-output image data) obtained by reading a paper image by the reading device in the same manner. Is stored in the image data storage unit 130 in association with the pre-output image data described above.

  On the other hand, if the output reading unit 190 does not exist in the image forming apparatus 100 or if automatic reading is not performed (NO in step S105 in FIG. 4 and NO in step S202 in FIG. 4), A user reads an image of a sheet on which an image has been formed using the document reading unit 110 or another reading device (not shown) (step S203 in FIG. 4), and the image data (post-output image data) obtained by the reading is The control unit 101 controls to store the image data storage unit 130 in association with the pre-output image data described above (step S204 in FIG. 4).

As the print processing of the image forming apparatus 100, the control unit 101 controls each unit so that a series of processes similar to the above are repeatedly executed for all of the instructed original image data (steps in FIG. 4). NO in step S208 → step S102, or
In step S208 in FIG. 4, YES → END).

  On the other hand, as uneven density correction processing, the control unit 101 is configured to divide the pre-output image data into a plurality of regions in the main scanning direction (see FIG. 5) and divide the post-output image data into a plurality of regions in the main scanning direction (see FIG. 6). Controls the image processing unit 140 (step S205 in FIG. 4). Here, the plurality of regions of the pre-output image data and the post-output image data are divided into a plurality of regions in the main scanning direction, and are set from the start position to the end position in the sub-scanning direction.

Further, the control unit 101 enters the input / output gradation characteristics indicating the correspondence relationship of the density of the same pixel for the pre-output image data and the post-output image data for each region divided into a plurality of regions in the main scanning direction. The output tone characteristic calculation unit 121 is controlled (step S206 in FIG. 4).
That is, the input / output gradation characteristic calculation unit 121 performs input / output of AREA_1 in the area AREA_1 in FIG. 5 and the area AREA_1 in FIG. 6 according to the density of the pre-output image data and the post-output image data for the same pixel. A gradation characteristic Fio_1 is generated. Similarly, the input / output gradation characteristic calculation unit 121 inputs AREA_2 in the area AREA_2 in FIG. 5 and the area AREA_2 in FIG. 6 according to the density of the pre-output image data and the density of the post-output image data for the same pixel. Output gradation characteristic Fio_2 is generated. Similarly, the input / output tone characteristic calculation unit 121 inputs AREA_3 for the same pixel in the area AREA_3 in FIG. 5 and the area AREA_3 in FIG. 6 according to the density of the pre-output image data and the density of the post-output image data. An output gradation characteristic Fio_3 is generated. Similarly, the input / output gradation characteristic calculation unit 121 inputs AREA_4 in the area AREA_4 in FIG. 5 and the area AREA_4 in FIG. 6 according to the density of the pre-output image data and the density of the post-output image data for the same pixel. An output gradation characteristic Fio_4 is generated. Similarly, the input / output gradation characteristic calculation unit 121 inputs AREA_5 in the area AREA_5 in FIG. 5 and the area AREA_5 in FIG. 6 according to the density of the pre-output image data and the density of the post-output image data for the same pixel. An output gradation characteristic Fio_5 is generated.

  An example of these input / output gradation characteristics Fio_1 to Fio_5 is shown in FIG. Here, the horizontal axis represents the density D_in of the pre-output image data, and the vertical axis represents the density D_out of the post-output image data. In the example of FIG. 7, the input / output gradation characteristics Fio_1 of AREA_1 and the input / output gradation characteristics Fio_5 of AREA_5 corresponding to the ends in the main scanning direction are after output than the other input / output gradation characteristics Fio_2 to Fio_4. It can be seen that the image density D_out is lowered. The characteristics shown here are merely examples, and are expected to vary depending on the configuration of the apparatus.

  The calculation of the above input / output gradation characteristics Fio_1 to Fio_5 is not obtained from one pre-output image data and post-output image data, but from a plurality of pre-output image data and post-output image data. This is desirable from the viewpoint of eliminating errors. However, since the image forming characteristics of the image forming unit 150 change and the input / output gradation characteristics change as time passes, the latest pre-output image data and post-output image data are heavily weighted, and the old pre-output image data It is desirable to obtain input / output gradation characteristics from a plurality of pre-output image data and post-output image data, with a smaller weighting for post-output image data.

Also, under the control of the control unit 101, the input / output gradation characteristic calculation unit 121 calculates a reference gradation characteristic Fio_ref as a reference input / output gradation characteristic, and the reference gradation characteristic Fio_ref is the reference gradation characteristic holding unit. 122 (step S207 in FIG. 4).
The generation of the reference gradation characteristic Fio_ref by the input / output gradation characteristic calculation unit 121 is performed when the pre-output image data and the post-output image data necessary for calculating the input / output gradation characteristic are sufficiently obtained. Is calculated by averaging the input / output gradation characteristics Fio_1 to Fio_5 of a plurality of regions. For example, as shown in FIG. 8, the reference gradation characteristics Fio_ref (solid line) are calculated by averaging the input / output gradation characteristics Fio_1 to Fio_5 (broken line). In this way, by calculating the reference gradation characteristic Fio_ref by averaging the input / output gradation characteristics Fio_1 to Fio_5, it is possible to correct the uneven density in each of the plurality of regions with a small correction amount.

  Note that the generation of the reference gradation characteristic Fio_ref is not obtained from one pre-output image data and post-output image data, but is obtained from a plurality of pre-output image data and post-output image data, thereby eliminating errors. It is desirable from the viewpoint of However, since the image forming characteristics of the image forming unit 150 change with time, the latest one can be obtained from a plurality of pre-output image data and post-output image data as a larger weight and an older one as a smaller weight. desirable.

  On the other hand, the generation of the reference gradation characteristic Fio_ref by the input / output gradation characteristic calculation unit 121 is when the pre-output image data and post-output image data necessary for calculating the input / output gradation characteristic are not sufficiently obtained. In this case, the input / output gradation characteristic (for example, Fio_3) of the region near the center in the main scanning direction may be held in the reference gradation characteristic holding unit 122 as the reference input / output gradation characteristic.

  Further, the generation of the reference gradation characteristic Fio_ref by the input / output gradation characteristic calculation unit 121 is performed when the pre-output image data and the post-output image data necessary for calculating the input / output gradation characteristic are not sufficiently obtained. Alternatively, when a fixed reference gradation characteristic is desired, an input / output gradation characteristic given in advance may be used. In this case, the input / output gradation characteristics provided by the user may be used, or when the image forming apparatus 100 is manufactured, the specific input / output gradation characteristics are held in advance in the reference gradation characteristic holding unit 122 as the reference gradation characteristics. May be. Note that the fixed reference gradation characteristics may be replaced with the above-described average of the input / output gradation characteristics of a plurality of regions as specified by the user.

Then, under the control of the control unit 101, the correction data calculation unit 123 calculates correction data for eliminating the difference between the input / output gradation characteristics Fio_1 to Fio_5 of the plurality of regions and the reference gradation characteristic Fio_ref (in FIG. 4). Step S208).
Here, the procedure for calculating correction data for eliminating the difference between the input / output gradation characteristic Fio_1 obtained in the area AREA_1 and the reference gradation characteristic Fio_ref will be described with reference to FIG.
(1) In the input / output gradation characteristic Fio_1 obtained in the area AREA_1, the post-output image density D_out_a is obtained corresponding to the pre-output image density D_in_a.
(2) When the reference gradation characteristic Fio_ref is applied instead of the input / output gradation characteristic Fio_1 obtained in the area AREA_1, the post-output image density D_out_a_ref is obtained corresponding to the pre-output image density D_in_a. That is, when a density equivalent to the post-output image density D_out_a_ref is obtained corresponding to the pre-output image density D_in_a, this corresponds to a state in which the input / output gradation characteristics match in each of the plurality of areas, and density unevenness is eliminated. Become.
(3) Therefore, the pre-output image density D_in_a ′ from which the post-output image density D_out_a_ref is obtained in the input / output gradation characteristic Fio_1 is calculated backward.
(4) Also in the area AREA_1, an ideal post-output image density D_out_a_ref can be obtained by correcting the pre-output image density D_in_a to the pre-output image density D_in_a ′ and then applying the input / output gradation characteristic Fio_1.
(5) Calculate correction data for correcting the pre-output image density D_in_a to the pre-output image density D_in_a ′ in the pre-output image density D_in_a of the area AREA_1.
(6) Similarly, when the input / output gradation characteristic Fio_1 is applied to the pre-output image densities D_in_0 to D_in_max in the area AREA_1, the pre-output image densities D_in_0 to D_in_0 to D_out_0_ref to D_out_max_ref are obtained. Correction data for converting D_in_max into pre-output image densities D_in_0 ′ to D_in_max ′ is calculated.

  The control unit 101 obtains the correction data calculated by the correction data calculation unit 123 as described above for each of a plurality of areas, and supplies the correction data to the image processing unit 140 in a format such as a lookup table. Then, the image processing unit 140 executes image processing before image formation using the correction data (step S103 in FIG. 4).

By such image processing, an image obtained by image formation by the image forming unit 150 is in a state that matches the input / output gradation characteristics equivalent to the reference gradation characteristics in all of the plurality of regions in the main scanning direction. That is, image formation is executed in a state where density unevenness in the main scanning direction is eliminated.
The above density unevenness correction processing is executed in parallel with image formation. Therefore, it is not necessary to print a dedicated test chart. Accordingly, it is possible to avoid a situation in which normal image formation is restricted by the print of the test chart and productivity is lowered. In addition, since it does not require the presence of a constant density region in the image, it can be executed in a normal state. Further, even when the normal image formation schedule is clogged, a test chart is not required, so that density unevenness can be corrected at any timing or periodically.

  FIG. 10 shows a state where the input / output gradation characteristic Fio_x is obtained only in a part of the density range. In this case, it is also difficult to calculate the reference gradation characteristic Fio_ref by averaging the input / output gradation characteristics of a plurality of regions. In such a case, it is desirable to use the reference gradation characteristic Fio_ref previously held in the reference gradation characteristic holding unit 122.

  Then, as described above in (1) to (6), in the input / output gradation characteristic Fio_x obtained in the area AREA_x, after applying the reference gradation characteristic Fio_ref corresponding to the pre-output image density D_in_b The pre-output image density D_in_b ′ from which the image density D_out_b_ref is obtained is calculated backward, and correction data for correcting the pre-output image density D_in_b to the pre-output image density D_in_b ′ is calculated. Similarly, correction data is calculated within a range where the input / output gradation characteristic Fio_x exists. Note that the problem occurs when the pre-output image data and post-output image data are obtained with only some of the gradations, because only the partial gradation range is the gradations necessary for correction. Absent.

  In the above description, it is assumed that input / output gradation characteristics are obtained in all of a plurality of regions divided in the main scanning direction, but the present invention is not limited to this. For example, photographic images may exist only on the right half in the main scanning direction on all pages, and only letters may exist on the left half of all pages. That is, when the pre-output image data and post-output image data are obtained only in a part of the area, the input / output gradation characteristics are calculated only in the part of the part of the area, and a predetermined reference level is calculated. Correction data may be generated based on the tone characteristics. In this case as well, there is no problem because only a part of the region is a region necessary for correction.

  Further, in the above description, when calculating the input / output gradation characteristics in a plurality of areas in the main scanning direction and generating correction data, a specific example is shown in which the areas are equally divided into five areas in the main scanning direction. However, it is desirable to be able to change the settings of a plurality of regions having different main scanning directions.

  For example, as a plurality of regions in the main scanning direction, a region that is roughly divided near the center in the main scanning direction, and a region that is finely divided near the end in the main scanning direction, thereby causing unevenness in density unevenness. Therefore, it is possible to calculate and correct appropriate density unevenness with high accuracy and with a minimum amount of calculation.

  In addition, when there is a margin in the calculation capability of the density unevenness detection unit 120, the area may be more fine than 5 areas. Thereby, calculation and correction of fine and appropriate density unevenness can be performed. Further, the number of regions divided in the main scanning direction may be increased or decreased according to the density unevenness distribution state (spatial frequency of density unevenness). In this case, the density unevenness distribution state, that is, the spatial frequency of the density unevenness may be obtained by image processing or based on the user's judgment. This makes it possible to calculate and correct appropriate density unevenness.

  In addition, when the correction data of each area obtained as described above exceeds a presumed range, the control unit 101 can determine that some abnormality has occurred in the image forming unit 150. In this case, it is also desirable to take various measures such as stopping image formation and notifying the call center.

[Effect obtained by the embodiment]
(1) Pre-output image data and post-output image when linear image formation in the main scanning direction is repeatedly executed in the sub-scanning direction orthogonal to the main scanning direction to execute two-dimensional image formation on the recording medium. Correction data that calculates the input / output gradation characteristics for each area that differs in the main scanning direction and eliminates the difference between the input / output gradation characteristics for each area and the reference input / output gradation characteristics Is calculated for each of a plurality of areas, and image processing is performed so that the pre-output image data is corrected by the correction data for each of the plurality of areas. For this reason, it is possible to detect and correct density unevenness occurring in image formation without requiring the printing of a dedicated test chart or the presence of a constant density region in the image. Accordingly, it is possible to avoid a situation in which normal image formation is restricted by the print of the test chart and productivity is lowered. In addition, the problem of consuming paper, toner, and the like is solved. Furthermore, even when the normal image formation schedule is clogged, a test chart is not necessary, so that density unevenness can be corrected at an arbitrary timing.

(2) By calculating the reference input / output gradation characteristics based on the average of the input / output gradation characteristics for each of the plurality of areas, it is possible to correct the uneven density in each of the plurality of areas with a small correction amount. .
(3) By using input / output gradation characteristics given in advance as the reference input / output gradation characteristics, there are few inputs of pre-output image data and post-output image data and there is not sufficient accumulation. In addition, it becomes possible to secure the reference input / output gradation characteristics. In addition, it is possible to correct density unevenness based on predetermined input / output gradation characteristics for each of a plurality of regions.

  (4) When necessary amounts of pre-output image data and post-output image data are obtained, a plurality of input / output gradation characteristics are calculated by calculating an average of input / output gradation characteristics for each of a plurality of areas. Thus, it is possible to correct the density unevenness of each area with a small correction amount. In addition, when the required amount of pre-output image data and post-output image data is not obtained, the input / output gradation characteristics given in advance are used as reference input / output gradation characteristics, so It becomes possible to correct the density unevenness based on the input / output gradation characteristics of the predetermined region.

  (5) When the pre-output image data and the post-output image data are obtained in only a part of the region or a part of the gradations, the input / output floor is obtained only in the part of the region or the part of the gradation A tone characteristic is calculated, and correction data is generated in a part of the region where the input / output gradation characteristic exists or a part of the gradation. In this way, even when there are few inputs of pre-output image data and post-output image data and a complete input / output gradation characteristic cannot be generated, density unevenness can be corrected in each of a plurality of regions. It becomes possible. In addition, when the pre-output image data and the post-output image data are obtained in only a part of the area or a part of the gradation, the part of the area or the part of the gradation is only an area necessary for the correction. Or since it is a gradation, a problem does not arise.

  (6) In the case of forming a color image on a recording medium using a plurality of color materials, the input / output gradation characteristics are calculated in pixels using only one of the color materials, so that other colors are obtained. Therefore, it is possible to accurately obtain and correct the input / output gradation characteristics caused by the uneven density of the target color without being affected by the color material.

  (7) When calculating the input / output gradation characteristics in a plurality of areas different in the main scanning direction, the setting of the plurality of areas different in the main scanning direction can be changed, and the setting of the areas in the input / output gradation characteristic calculation unit By calculating correction data for each area according to the change, depending on the presence or absence of density unevenness, depending on the required accuracy of density unevenness, and depending on the allowable calculation amount Therefore, it is possible to calculate and correct an appropriate density unevenness.

  (8) As a plurality of regions different in the main scanning direction when calculating the input / output gradation characteristics, a region roughly divided near the center in the main scanning direction and a region finely divided near the end in the main scanning direction are By doing so, it is possible to calculate and correct the appropriate density unevenness with high accuracy and with the minimum amount of calculation at the end portion where the density unevenness is likely to occur.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Control part 102 Communication part 104 Storage part 103 Operation display part 105 Paper feed part 107 Conveyance part 110 Original reading part 130 Image data storage part 140 Image processing part 150 Image forming part 190 Output matter reading part

Claims (11)

An image processing apparatus used for image processing in an image forming apparatus that executes linear image formation in a first direction repeatedly in a second direction orthogonal to the first direction to execute two-dimensional image formation on a recording medium. There,
Correspondence relationship of the density of the same pixel between pre-output image data used for image formation by the image forming apparatus and post-output image data obtained by scanning an image formed on the recording medium by the image forming apparatus An input / output gradation characteristic calculating unit that calculates the input / output gradation characteristic for each of a plurality of different areas in the first direction;
A correction data calculation unit that calculates correction data for each of the plurality of regions to eliminate a difference from the reference input / output tone characteristics for the input / output tone characteristics for each of the plurality of regions;
An image processing unit that corrects the pre-output image data with the correction data for each of a plurality of areas and performs image processing so as to eliminate the difference in the input / output gradation characteristics for each of the plurality of areas that differ in the first direction; Yes, and
The input / output gradation characteristics indicate a correspondence relationship between the density of the plurality of pre-output images in a region and the density of the post-output image data of the same pixel for each density of the pre-output image. A featured image processing apparatus. The input / output gradation characteristic calculation unit calculates the reference input / output gradation characteristic based on an average of the input / output gradation characteristics for each of a plurality of regions;
The image processing apparatus according to claim 1. The input / output gradation characteristic calculation unit uses a predetermined input / output gradation characteristic as the reference input / output gradation characteristic,
The image processing apparatus according to claim 1. The input / output tone characteristic calculation unit, when the necessary amount of the pre-output image data and the post-output image data necessary for calculating the input / output tone characteristic is obtained, Calculate the reference input / output gradation characteristics by the average of the input output gradation characteristics,
When the required amount of the pre-output image data and the post-output image data is not obtained, the input / output gradation characteristics given in advance are used as the reference input / output gradation characteristics,
The image processing apparatus according to claim 1. When the pre-output image data and the post-output image data are obtained in a partial area or only in a partial gradation, the input / output gradation characteristic calculating unit The input / output gradation characteristics are calculated using only the gradation of the part,
The correction data calculation unit generates the correction data in a partial region where the input / output gradation characteristics exist or a partial gradation.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. In the case where the image forming apparatus forms a color image on the recording medium using a plurality of color materials,
The input / output gradation characteristic calculation unit calculates the input / output gradation characteristic in a pixel using only one of the color materials;
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The input / output gradation characteristic calculation unit can change the setting of the plurality of different areas in the first direction when calculating the input / output gradation characteristics in the plurality of areas different in the first direction,
The correction data calculation unit calculates the correction data for each region in accordance with the region setting change in the input / output gradation characteristic calculation unit.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The input / output tone characteristic calculation unit includes a plurality of regions different in the first direction when calculating the input / output tone characteristics, and a region roughly divided near the center of the first direction, the first direction In the vicinity of the edge, the area should be finely divided.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The image processing apparatus according to any one of claims 1 to 8,
An image forming unit that forms an image based on pre-output image data image-processed by the image processing device;
An image reading unit that reads the image formed by the image forming unit and generates the output image data;
An image forming apparatus comprising: The image processing apparatus according to any one of claims 1 to 8,
An image forming apparatus that forms an image based on pre-output image data image-processed by the image processing apparatus;
An image reading device for reading the image formed by the image forming device and generating the output image data;
An image forming system comprising: An image processing apparatus used for image processing in an image forming apparatus that executes linear image formation in a first direction repeatedly in a second direction orthogonal to the first direction to execute two-dimensional image formation on a recording medium. An image processing method comprising:
Correspondence relationship of the density of the same pixel between pre-output image data used for image formation by the image forming apparatus and post-output image data obtained by scanning an image formed on the recording medium by the image forming apparatus Calculating the input / output gradation characteristics for each of a plurality of different areas in the first direction,
Calculating correction data for each of the plurality of areas to eliminate the difference between the input / output gradation characteristics for each of the plurality of areas and a reference input / output gradation characteristic;
Correcting the pre-output image data with the correction data for each of a plurality of areas to perform image processing so as to eliminate the difference in the input / output gradation characteristics for each of the plurality of areas different in the first direction ;
The input / output tone characteristics indicate a correspondence relationship between the density of the plurality of pre-output images in a region and the density of the post-output image data of the same pixel for each density of the pre-output image. An image processing method characterized by the above.