JP5288918B2 - Image forming apparatus, control method therefor, and program - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image in the same area on a recording medium by a plurality of recording scans of a recording head that discharges a plurality of recording agents having different densities, a control method therefor, and a program.

  As an example of a printer using a recording head provided with a plurality of recording elements, a color ink jet printer using a recording head provided with a plurality of ink discharge ports (nozzles) has been known.

  Unlike a monochrome printer that records only a character, a color printer that records a color image image requires stable recording for various elements such as color development, gradation, and uniformity. In particular, the uniformity is easily affected by slight nozzle unit variations that occur in the printing element array manufacturing process. Such variations make the discharge amount and direction of each nozzle unstable, resulting in uneven density in the recorded image. May occur.

  In particular, the following may occur in a serial-type ink jet printer that performs recording by scanning the recording head in a direction different from the arrangement direction of the plurality of recording elements, for example, a direction orthogonal thereto. In other words, the density unevenness caused by the above-described nozzle unit variation appears in the recorded image as stripes, which may reduce the image quality.

  In order to avoid this, it is common to apply a recording method called a multi-pass recording method. In this multi-pass recording method, in a conventional serial type ink jet printer, the recording data to be recorded in the same recording area is divided into a plurality of groups, and the same recording is performed by a plurality of recording scans sandwiching the recording medium conveyance operation. This is a method of recording an area divided into a plurality of times.

  According to the multi-pass recording method, a recording line that can be recorded by one recording scan can be formed by a plurality of recording scans by different nozzles, so that the influence on the image unique to each nozzle is reduced. Is done. In addition, since recording is performed not only by the end nozzles but also by the central nozzles at the boundary for each recording scan, the connecting stripes are not noticeable, and density unevenness in the recorded image is reduced.

  Here, the multi-pass recording method will be described.

  FIG. 14 is a diagram showing a recording head portion of a conventional ink jet printer.

  The recording head unit 101 has six basic colors of dark C (dark cyan), light C (light cyan), dark M (dark magenta), light M (light magenta), Y (yellow), and K (black) ink. An ink jet recording head including a nozzle row for discharging is configured. The recording head unit 101 performs one printing in the nozzle row direction (sub-scanning direction) by one scanning in the main scanning direction by the recording head of each ink color. When one printing is completed, the recording medium is conveyed in the sub-scanning direction orthogonal to the main scanning direction.

  FIG. 15 is a diagram for explaining multi-pass printing by a printer using the print head shown in FIG.

  Reference numeral 1501 denotes a monochrome image area formed by the recording head unit 101. In the image area 1501, a sub-scan that is a conveyance scan of the recording medium 202 is performed once for each main scanning of the recording head unit 101, and an image is formed on the recording medium 202 by N main scannings. The conveyance amount of the recording medium 202 in the sub-scanning direction orthogonal to the main scanning direction is 1 / N nozzle height, and the image is superimposed on the same image area by N main scannings of the recording head unit 101. Formed.

  Here, N = 4 is taken as an example, and images are formed in four image areas A, B, C, and D by four main scans. In the image areas A to D in FIG. 15, image formation is performed by exclusive dot arrangement, so that one image is formed without overlapping dot positions.

  Processing from converting the multi-valued image data transferred to the ink jet printer into N-value, converting it into head drive data, and ejecting ink from the nozzles of the recording head unit 101 according to the head drive data The contents will be described with reference to FIG.

  (1) The image data storage device 1601 stores multi-value RGB image data transferred from the host computer. Then, the image data storage device 1601 reads out multi-value RGB image data for each band (nozzle height required for one main scan) and outputs it to the γ conversion circuit 1602.

  (2) The γ conversion circuit 1602 performs input γ conversion for performing luminance correction on the multi-value RGB image data.

  (3) The color conversion pre-stage circuit 1603 converts the multi-value RGB image data into the multi-value R′G′B using a lookup table for color-converting the multi-value RGB image data into the multi-value R′G′B ′ image data. 'Convert color to image data.

  (4) In the color conversion post-stage circuit 1604, the multi-value R′G′B ′ image data is converted into the multi-value R by a look-up table for color-converting the multi-value R′G′B ′ image data into multi-value C, Cc, M, Mm, Y, K image data. 'G'B' image data is color-converted into multi-value C, Cc, M, Mm, Y, K image data. Here, C, Cc, M, and Mm correspond to dark C (dark cyan), light C (light cyan), dark M (dark magenta), and light M (light magenta), respectively.

  (5) The gradation reduction circuit 1605 converts M-value (M> N) multi-value image data into N-value image data by an error diffusion method (ED). Here, N = 2.

  (6) The mask memory 1608 stores data (mask data) having a complementary relationship that enables 100% dot arrangement by a plurality of scans. The N-value image data is ANDed with the mask data in the mask memory 1608 and transferred to the print control unit 1606 (head controller).

  (7) The print control unit 1606 converts the calculated image data into head drive data, and performs printing by ejecting ink from the recording head unit 101.

  According to the above-described method, the image of the predetermined region is formed as one image by a plurality of main scans. That is, image formation in a predetermined area is executed in a plurality of times using a plurality of nozzles. Accordingly, it is possible to reduce density unevenness caused by variations in the characteristics of the ejection ports (nozzles), such as deviation of the mounting position of the recording head with respect to the recording head unit 101. As described above, the method of relatively reducing density unevenness by dispersing density unevenness caused by the unique characteristics of the discharge port of the recording head on the recording medium is called a multi-scan (also called multi-pass) method. .

  On the other hand, in such an ink jet printer, the ink absorbability of the recording medium to be recorded is also an important factor, and in particular, it is known that the ink bleed characteristic on the recording medium has a great influence on the image quality. ing.

As an index indicating the ink bleed characteristic of the recording medium, “bleed rate” is known. This indicates how many times the diameter of the ink droplets ejected from the nozzles of the recording head spread on the recording medium,
“Bleeding rate” = given dot diameter / discharged ink droplet diameter on the recording medium.

  For example, if an ink droplet having a flying diameter of 30 μm forms a dot diameter of 90 μm on the recording medium, the “bleeding rate” of the recording medium is 3.0. This “bleeding rate” has a different numerical value for each recording medium. For example, coated paper has high ink absorptivity and shows a small “bleed rate”, while ordinary plain paper does not have high ink absorbency and has a large “bleed rate”. Indicates.

  FIG. 17 is a graph showing the density with respect to the ink amount on the recording medium.

  Reference numeral 1701 denotes the density characteristic of the coated paper, and reference numeral 1702 denotes the density characteristic of the plain paper. When compared with the case where a small amount of ink is ejected from the recording head, the density of the coated paper, which is a recording medium having a small “bleed rate”, has a low image density on the recording medium. On the other hand, in the density characteristic 1702 of plain paper that is a recording medium having a large “bleed rate”, the image density on the recording medium is high.

  However, this shows only a tendency that the density characteristic 1702 temporarily increases the image density because the larger the blur on the recording medium, the smaller the margin of the recording medium. After that, the image density indicated by the density characteristic 1702 does not rise linearly with respect to the ink amount, and is saturated when the limit of the ink absorption amount comes. The density does not increase no matter how much the ink amount is increased. Does not rise. In other words, the image density that can be expressed on the recording medium is determined according to the limit of the ink absorption amount.

  Furthermore, if the amount of ink that can be applied varies depending on the recording medium and exceeds the limit, new adverse effects such as ink overflow may be caused. When recording is performed using inks having different densities on the recording medium, recording is performed using only dark ink on the recording medium having the density characteristic 1702, and dark ink and light ink are used on the recording medium having the density characteristic 1701. This is the reason why it is common to record on both.

  Therefore, conventionally, at the time of development, several recording media to be printed are assumed, and the image processing table, the image correction processing unit, and the light and dark ink distribution are set so that the recording density is optimum for each recording medium. A method is employed in which tables and the like are individually created and implemented.

  However, it is impossible to deal with recording media that are not assumed by these methods, and a recording method called head shading has been proposed as a new method (Patent Document 1).

  Here, the head shading will be described.

  FIG. 18 is a diagram showing a method disclosed in Patent Document 1. In FIG.

  First, a test pattern for determining a correction value set in advance using a recording head is recorded on a recording medium (step S11). Next, the recording density of the recorded test pattern is read by a scanner (step S12). After appropriately correcting the position of the read image, the density of the image is averaged in the column direction (main scanning direction) (step S13).

  Next, it assigns to the raster corresponding to each nozzle of the recording head (step S14). The change in the recording density occurs due to a deviation in the ink discharge amount and discharge direction for each nozzle, or ink bleeding on the recording medium. Next, the correction value of the recording density for each nozzle is calculated and determined from the density data assigned for each raster (step S15).

  Then, the image data for each nozzle is corrected based on the correction value (step S16). Specifically, by changing the γ table for each nozzle or changing the drive table for each nozzle, the ink ejection amount, the distribution of dark and light inks, and the like are changed. By correcting the image data based on such correction values, the density correction is performed so that the raster recorded darkly without correction is thinned. Further, the density correction is performed so that the raster that is thinly recorded in the state without correction is darkened.

  Further, Patent Document 2 has been proposed as another prior art that performs image processing using an optimal image processing table, image correction processing by an image correction processing unit, and ink amount control for an unexpected recording medium. .

According to the technique disclosed in Patent Document 2, even if it is an unexpected recording medium, a reading medium is created by forming an image of a test pattern capable of determining a more suitable ink amount. An image forming method has been proposed in which parameters necessary for image processing are suitably set based on the interpretation medium to reduce ink overflow on the recording medium.
JP-A-5-69545 JP 2003-334934 A

  However, in the conventional method, it is necessary to acquire data for performing correction for density correction of an arbitrary recording medium that does not include an image processing table or an image correction processing unit. That is, it is necessary to record a correction image (test pattern) on a recording medium and read the density of the recorded image. Here, when it is necessary to read a large number of images for correction, there is a problem that much time is spent for the reading operation, and the overall adjustment time is lengthened.

  Furthermore, if there is a change in the recording medium after recording the test pattern, or if there are variations in individual ink absorption characteristics of the recording medium, it is impossible to cope with it. Further, since the correction amount varies depending on the input density and the print mode, there are disadvantages that the capacity of the image processing table for managing the correction coefficient is increased and the processing becomes complicated.

  The present invention has been made in view of the above problems, and provides an image forming apparatus, a control method thereof, and a program capable of effectively and effectively reducing density unevenness that may occur due to multipass printing. Objective.

In order to achieve the above object, an image forming apparatus according to the present invention comprises the following arrangement. That is,
An image forming apparatus for forming an image in the same area on a recording medium by a plurality of recording scans of a recording head that discharges a plurality of recording agents having different densities,
Input means for inputting image data;
A first color conversion process for color conversion to color component image data corresponding to a recording agent having a high density among the plurality of recording agents having different densities, and colors corresponding to the recording agents of the plurality of recording agents having different densities. Color conversion means for color-converting image data input by the input means using any of the second color conversion processing for color conversion to component image data;
Wherein a plurality of times of printing scan, the printing scan of the recording head prior to acquiring the information indicating the absorption rate of said recording agents definitive on the recording medium acquisition means,
Based on the absorption rate of the recording agent acquired by the acquisition unit, the first color conversion process is selected when the absorption rate is low, and the second color conversion process is selected when the absorption rate is high. Switching control means to be executed by the color conversion means.

  According to the present invention, it is possible to provide an image forming apparatus that can efficiently and effectively reduce density unevenness that may occur due to multipass printing, a control method therefor, and a program.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present invention, a sensor for reading a recorded image on a recording medium is provided in parallel with the recording element array of the recording head to detect bleeding of a recording dot in preceding recording in multipass recording. In accordance with the “bleed rate” of the detected recording dots, the distribution of the dark and light inks in the subsequent recording is controlled. That is, control is performed using dark and light inks (a plurality of recording agents having different densities) for a recording medium with a low bleeding rate, and using only dark ink for a recording medium with a high bleeding rate.

  As a result, even with an unexpected recording medium that does not have an image processing table or an image correction processing unit, recording with an optimal ink density is possible.

  Furthermore, by executing the image correction process during printing, an adjustment step for an unexpected recording medium is unnecessary, and the quality of the recorded image can be maintained.

  Note that the recording density described below means a density obtained by detecting an image recorded on a recording medium by a sensor unless otherwise noted, and the printing density prints an image on the recording medium. Therefore, it is assumed that it means the density of the image data.

<Embodiment 1>
First, in an ink jet recording apparatus that is an image forming apparatus, a sensor unit that detects bleeding of a recording dot on a recording medium is provided in the recording head, and the optimum density for the recording medium is determined according to the “bleeding rate” of the detected recording dot. An example of performing ink switching control will be described.

  FIG. 1 is a diagram showing a recording head unit of an ink jet recording apparatus according to Embodiment 1 of the present invention.

  The recording head unit 101 has six basic colors of dark C (dark cyan), light C (light cyan), dark M (dark magenta), light M (light magenta), Y (yellow), and K (black) ink. An ink jet recording head having an ejection through nozzle array is configured. Here, the recording head unit 101 on which six color ink jet recording heads (hereinafter abbreviated as recording heads) are mounted is shown as an example, but a recording head having a larger number of ink colors may be used. The way of arranging the ink colors is not particularly limited.

  The recording head unit 101 performs one printing in the nozzle row direction (sub-scanning direction) by one scanning in the main scanning direction by the recording head of each ink color. When one printing is completed, the recording medium is conveyed in the sub-scanning direction orthogonal to the main scanning direction.

  Reference numeral 102 denotes a sensor unit for reading the recording dot diameter on the recording medium. In FIG. 1, the sensor unit 102 is illustrated with the same length as the recording head as an example, but the length and width are not particularly limited. Further, regarding the arrangement of the sensor unit 102, it is assumed that the sensor unit 102 is arranged at a position preceding the recording head for K (black) in the main scanning direction. In other words, the sensor unit 102 is arranged on one end side of both ends of the recording head unit 101. However, in consideration of reciprocal printing of main scanning, the sensor unit 102 is also arranged on the other end side, and the sensor unit 102 is arranged on both ends. May be arranged. By disposing the sensor unit 102 at a position where scanning precedes in the main scanning direction, recording by the recording head unit 101 is possible while detecting the recording dot diameter of the previously recorded image.

  FIG. 2 is a diagram illustrating a state in which the sensor unit according to the first embodiment of the present invention reads the recording dot diameter of the image recorded on the recording medium.

  The sensor unit 102 includes a light emitting unit 102a and a light receiving unit 102b therein, and irradiates light onto the recording dots 201 recorded on the recording medium 202 from the light emitting unit 102a. Then, by the irradiation, a light amount reflected according to the density of the recording dot 201 is received by the light receiving unit 102b. Based on the light reception result, the sensor unit 102 detects the density of the recording dot 201.

  It is assumed that the light receiving unit 102b has sufficient resolution and sensitivity to detect the recording dot diameter (dot profile).

  FIG. 3 is a block diagram showing the configuration of the image forming apparatus according to the first embodiment of the present invention.

  The image forming apparatus according to the first embodiment includes an image data storage device 301, an image processing unit 1000, a print control unit 307, a recording head 308, a sensor unit 102, a blur detection circuit 311, and a switching control unit 312. The image processing unit 1000 includes a γ conversion circuit 302, a color conversion pre-stage circuit 303, a color conversion post-stage circuit 304, a pass division circuit 305, and a gradation reduction circuit 306.

  In the image forming apparatus described in each embodiment of the present invention, for example, scanning of the recording head in the main scanning direction and conveyance of the recording medium in the sub scanning direction orthogonal to the main scanning direction are repeated alternately. An image forming apparatus for forming an image by an ink jet method for forming an image. In addition to the various components shown in FIG. 3, this image forming apparatus is actually mounted with components such as a CPU and a memory (ROM and RAM) for realizing print control by the ink jet method.

  In FIG. 3, by this image forming apparatus, the transferred multi-value image data is converted to N-value, converted into head drive data, and ink is ejected from the nozzles of the print head according to the head drive data until printing is performed. Processing will be described.

  (1) The image data storage device 301 stores multi-value RGB image data transferred from the host computer. Then, the image data storage device 301 reads the multi-value RGB image data for each band and outputs it to the input γ conversion circuit 302.

  (2) The γ conversion circuit 302 performs input γ conversion for performing luminance correction on the multi-value RGB image data.

  (3) The color conversion pre-stage circuit 303 converts the multi-value RGB image data into the multi-value R′G′B by a lookup table for color-converting the multi-value RGB image data into the multi-value R′G′B ′ image data. 'Perform color conversion to image data.

  (4) The color conversion post-stage circuit 304 converts the multi-value R′G′B ′ image data into the multi-value CCcMMMYK using a lookup table for converting the multi-value R′G′B ′ image data into the multi-value CCcMMmYK image data. Perform color conversion to image data (color component image data). Here, color conversion means separation into ink colors.

  The color conversion post-stage circuit 304 starts from four-color conversion (R′G′B ′ → CMYK) using only dark ink (at this time, data “0” is stored in Cc and Mm. Suppose) Then, the color conversion post-stage circuit 304 performs a color conversion process for switching from the four color conversion to the six color conversion including dark and light inks (R′G′B ′ → CCcMMmYK) according to a command from the switching control unit 312.

  In other words, the color conversion post-stage circuit 304 performs the first color conversion process for converting into color component image data corresponding to dark ink (ink with high density), and the second color for converting into color component image data corresponding to each of dark and light inks. Select and execute conversion processing adaptively.

  (5) The pass division circuit 305 performs density conversion on the multi-value CCcMMmYK image data in accordance with the number of pass divisions of the multi-scan method (generates pass data (divided image data) for each pass). Here, the multi-scan method is a method in which the same area on the recording medium is scanned by the recording head 308 a plurality of times (N times: N = natural number) to complete image formation for the same area.

  For example, when the number of pass divisions = 2 (2 passes), image data obtained by multiplying multi-value CCcMMmYK image data by 0.5 is formed. When the number of pass divisions is 4 (4 passes), image data obtained by multiplying multi-value CCcMMmYK image data by 0.25 is formed. This method is an example in which the input density is divided equally, and it is not necessarily required to be equal.

  (6) In the gradation reduction circuit 306, for example, M-value image data of M (M> N: M and N are both natural numbers) values are converted into N-value image data for each pass by an error diffusion method (ED). Converted into (lower gradation). That is, gradation conversion (lower gradation) is performed to a gradation lower than the current gradation.

  (7) The gradation reduction circuit 306 transfers the N-value image data (here, N = 2, that is, binary image data) to the print control unit 307 (head controller).

  (8) The print control unit 307 converts the N-value image data into head drive data, and performs printing by ejecting ink from the recording head 308 using the head drive data.

  (9) The sensor unit 102 detects the profile of the recording dot in the preceding recording. The detected recording dot profile is converted into a “bleed rate” by the blur detection circuit 311. The blur detection circuit 311 will be described in detail later.

  (10) Based on the “bleeding rate” calculated by the blur detection circuit 311, the switching control unit 312 performs color conversion post-stage circuit 304 so that printing is performed with ink suitable for the recording medium on which recording is currently performed. In response to this, a command for performing dark / light ink switching control is output. The dark / light ink switching control will be described in detail later.

  FIG. 4 is a diagram showing the shape of the recording dots on each recording medium when ink is ejected from the recording head and recording is performed on two recording media having different ink absorbability according to the first embodiment of the present invention. is there.

  401 is an image diagram of ink droplets ejected from the nozzles of the recording head and in flight, and Sn indicates the dot diameter of the ink droplets. Here, Sn is the dot diameter of the ink droplet measured in the shipping inspection of the recording head 308. This dot diameter information is unique information stored in a non-volatile memory (not shown) inside the recording head unit 101. In the first embodiment, Sn is treated as an ideal dot diameter (reference dot diameter).

402 is an image diagram of a recording dot when an ink droplet has landed on the coated paper, and Pn_1 indicates the dot diameter. Coated paper has a high ink absorbability. For this reason, the recording dots 402 formed by the landed ink droplets do not protrude so much with respect to the diameter Sn of the ink droplet 401, that is, tend not to bleed very much. When the “bleed rate” as an index indicating the ink bleed characteristic of the recording medium is calculated, in the case of the recording dot 402, the bleed rate is 1.20 = Pn_1 / Sn.
Is calculated.

403 is an image diagram of a recording dot when an ink droplet has landed on plain paper, and Pn_2 indicates the dot diameter. Plain paper has a characteristic of low ink absorbability. For this reason, the recording dots 403 formed by the landed ink droplets protrude greatly with respect to the diameter Sn of the ink droplet 401, that is, tend to blur greatly. In the case of the recording dot 403, the bleeding rate is
2.00 = Pn_2 / Sn
Is calculated.

  However, the numerical value of the “bleeding rate” calculated here is a numerical value as a specific example for explaining the first embodiment, and is different from an actual numerical value.

  FIG. 5 is a flowchart showing the “bleed rate” detection process executed by the blur detection circuit according to the first embodiment of the present invention.

  This “bleeding rate” detection process is a process for detecting the blurring of the recording dots in the preceding printing. In the case of multi-pass printing, the “bleeding rate” detection process is executed for the printing result of the first pass in the second pass. .

  First, assuming that the Nth pass print scan is being performed, the sensor unit 102 reads the preceding print, that is, the print result of the (N-1) th pass. Then, the blur detection circuit 311 binarizes the reading result with a predetermined threshold value, and the dot of the recording dot is calculated from the continuous number (or area) of the bit (usually 0) on which the recording dot is applied. The diameter is calculated and input as the recording dot diameter Pn (step S21).

  Next, the blur detection circuit 311 refers to the dot diameter Sn (ink droplet 401 in FIG. 4), which is an ideal dot diameter, from the internal memory of the recording head 308 (step S22). The blur detection circuit 311 divides the input dot diameter Pn by the ideal dot diameter Sn to calculate a “bleed ratio” (step S23).

  Then, the blur detection circuit 311 outputs a blur detection completion signal notifying that the calculation of the “bleed rate” is completed at the time of the current N-th recording scan (step S24). The blur detection circuit 311 notifies the switching control unit 312 of the blur detection completion signal as a calculated “bleed rate” (step S25).

  FIG. 6 is a flowchart showing color conversion switching control processing executed by the switching control unit according to the first embodiment of the present invention.

  First, in the initial state, the switching control unit 312 instructs the color conversion post-stage circuit 304 to perform four-color conversion (R′G′B ′ → CMYK) (step S31). At this time, “0” is set as the value of the image data of Cc and Mm in FIG. Next, the switching control unit 312 resets the detection counter that counts the detection count to “0” (step S32). This detection counter is a counter that is incremented when the “bleed rate” is smaller than the threshold value Th1.

  Next, the switching control unit 312 determines whether a blur detection completion signal is received from the blur detection circuit 311 (step S33). If the blur detection completion signal has not been received (NO in step S33), the switching control unit 312 waits until it is received. On the other hand, when the blur detection completion signal is received (YES in step S33), the switching control unit 312 inputs the “bleed rate” included in the blur detection completion signal (step S34).

  Next, the switching control unit 312 compares the input “bleed rate” with the threshold Th1 (step S35). The threshold value Th1 (first threshold value) here generally indicates whether the “bleed rate” is a recording medium having a higher ink absorption rate or a lower ink absorption rate than the threshold value Th1. This is a predetermined value for determination. The threshold Th1 can be set in advance in the image forming apparatus main body.

  When the input “bleed rate” is smaller than the threshold Th1 (YES in step S35), the switching control unit 312 increments the detection counter (step S36). On the other hand, when the input “bleed rate” is equal to or greater than the threshold Th1 (first threshold or greater) (NO in step S35), the switching control unit 312 returns to step S33.

  Next, the switching control unit 312 determines whether or not the counter value of the detection counter is greater than a predetermined value Th2 (step S37). The predetermined value Th2 (second threshold value) here is a predetermined value for setting a plurality of trials in order to prevent erroneous discrimination and improve detection accuracy. That is, the number of times that the “bleeding rate” is smaller than the threshold value Th1 exceeds the predetermined value Th2 here, so that it is possible to more accurately determine a recording medium having a high ink absorption rate. The predetermined value Th2 can also be set in the image forming apparatus main body in advance.

  If the counter value of the detection counter is less than the predetermined value Th2 (NO in step S37), the process returns to step S33. On the other hand, when the counter value of the detection counter is larger than the predetermined value Th2 (YES in step S37), the switching control unit 312 determines that the recording medium used for image formation is a recording medium having a high ink absorption rate, It is determined that the light ink can be used (step S38). Then, the switching control unit 312 instructs the color conversion post-stage circuit 304 to switch the color conversion from the four-color conversion to the six-color conversion (R′G′B ′ → CCcMMmYK) (step S39).

  According to this color conversion switching control process, while the state where the “bleed rate” is equal to or greater than the threshold Th1 (greater than the threshold) continues, the steps S33 to S35 are looped, and at the end of recording on one recording medium at the maximum. This “bleeding rate” is cleared. That is, this color conversion switching control process starts from four color conversion, detects a predetermined number of blurs, and continues four color conversion until it can be determined that the detection medium is a recording medium having a high ink absorption rate. When it is determined that the recording medium has a high rate, switching to six-color conversion is performed.

  FIG. 7 is a diagram showing a dot profile that is a characteristic of the dot diameter according to the first embodiment of the present invention.

  Reference numeral 701 denotes a dot profile of coated paper having an ink absorption rate higher than a predetermined value, and reference numeral 702 denotes a dot profile of plain paper having an ink absorption rate lower than a predetermined value.

  In the first embodiment, as shown in FIG. 7, the dot diameter Rn on the recording medium is detected from the continuous number (or area) of pixels when the dot profile is binarized. Therefore, if the ideal dot diameter Sn is a dot count S corresponding to the continuous number (or area) Rn of pixels when the dot profile is binarized, whether or not the recording medium has a higher ink absorption rate than a predetermined value. Such a determination can be made using, for example, the following expression.

Rn <S × (Bleeding rate threshold Th1) = Th3
That is, the threshold value Th3 can be determined simply by setting a value corresponding to S × (the blurring rate threshold value Th1) and comparing the dot diameter Rn with the threshold value Th3.

  As described above, according to the first embodiment, whether the recording medium currently recording by the blur detection circuit 311 and the switching control unit 312 is a recording medium having an ink absorption rate higher or lower than a predetermined value. Determine. Then, based on the determination result, the image forming apparatus performs color conversion switching control. In this way, by performing dark and light ink distribution control suitable for a recording medium, it is possible to reduce density unevenness due to blurring of recording dots even when recording on an unexpected recording medium.

  In addition, by executing this control in real time during printing, offline processing such as test pattern printing, test pattern reading, and parameter setting in head shading is unnecessary, and high-speed processing is possible. In addition to this, it is possible to follow a mismatch with a recording medium specified by the print setting or a change over time due to an unknown recording medium or a recording medium change after the print setting is confirmed.

<Embodiment 2>
In the second embodiment, as a configuration example 1, an example of 4-pass printing that imposes restrictions on the pass division circuit 305 in order to generate a recording dot pattern that is not erroneously detected by the sensor unit 102 in the pass division circuit 305 will be described. .

(Configuration example 1)
FIG. 8 is an image diagram showing the arrangement of recording dots on the recording medium according to the second embodiment of the present invention.

  The numerical value on the left indicates the recording duty. As shown in FIG. 8, in recording with a recording duty of 12.5% or 25%, recording is performed without overlapping adjacent recording dots. In contrast, when the recording duty is 37.5%, the overlapping of the recording dots occurs, and when the recording duty is 50%, the recording dots cover most of the recording medium.

  When it is assumed that the sensor unit 102 in FIG. 2 reads the recording dot diameter, if adjacent recording dots overlap each other, an accurate recording dot diameter cannot be detected. Therefore, in order to generate a recording dot pattern that is not erroneously detected by the sensor unit 102, at least the recording duty must be lower than 25%, and preferably the recording duty should be 12.5%. However, the recording duty cannot be reduced in all passes in multi-pass recording. Therefore, in the second embodiment, a description will be given of a configuration in which the recording duty is reduced for the first pass print data and a recording dot pattern that does not detect erroneously is generated when the sensor unit 102 reads the recording dot diameter.

  FIG. 9A is a block diagram illustrating a configuration example 1 of the image forming apparatus according to the second exemplary embodiment of the present invention.

  In particular, in FIG. 9A, a first restriction unit 801 that restricts the recording dot pattern generated in the pass division circuit 305 is configured with respect to the configuration of the image forming apparatus in FIG. 3 of the first embodiment. Here, the same components as those in FIG. 3 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The first constraint unit 801 imposes a constraint on the pass division circuit 305 to reduce the density ratio of the divided image data in the first pass (first print scan). Specifically, as described with reference to FIG. 8, in the first pass, there is a restriction that the recording duty is a density ratio of 12.5% so that adjacent recording dots do not overlap each other.

  FIG. 9B is a block diagram illustrating a detailed configuration of main parts (pass division circuit, gradation reduction circuit, and print control unit) of the image processing unit of the image forming apparatus of FIG. 9A according to the second exemplary embodiment of the present invention.

  In FIG. 9B, reference numeral 600 denotes an image signal for one color of ink output from the color conversion post-stage circuit 304. In FIG. 9B, the image signal 600 is C (dark cyan). Further, the color conversion post-stage circuit 304 initially starts with four-color conversion using only dark ink, and it is assumed that data “0” is present in Cc and Mm during four-color conversion. Then, the color conversion post-stage circuit 304 performs a color conversion process to switch to six color conversion including dark and light inks when a switching signal from the switching control unit 312 is input.

  Reference numeral 601 denotes a detection signal from the sensor unit 102. The blur detection circuit 311 calculates a “bleed rate” from the recording dot diameter detected by the sensor unit 102. The switching control unit 312 controls the operation of the color conversion post-stage circuit 304 in accordance with the “bleed rate”. The switching signal storage unit 313 holds the switching signal from the switching control unit 312.

  Here, it is assumed that the switching signal storage unit 313 executes blur detection at the beginning of recording, and fixes the color conversion control in subsequent recording. In this case, when color conversion switching is confirmed by blur detection, the switching signal storage unit 313 holds the switching signal, and in subsequent recording, color conversion is executed based on the switching signal.

  Reference numeral 603 denotes a path division table that stores path division coefficients for dividing into multipaths. 605_1 to 605_4 are a first pass division coefficient K1 to a fourth pass division coefficient K4, respectively. It is the pass division table 603 that determines the print density in each pass when performing four-pass printing, in which the division factors K1, K2, K3, and K4 indicate the division ratio of each pass. ing.

Each division factor is
0 ≦ Ki ≦ 1 (i: 1, 2, 3, 4)
K1 + K2 + K3 + K4 = 1
It is.

  In the case of 4-pass printing, for example, K1, K2, K3, and K4 can each be a value of 0.25 (equal division). Alternatively, K1, K2, K3, and K4 are 0.1, 0.2, 0.3, and 0.4, respectively, as values that decrease the printing ratio of the first pass and gradually increase the printing ratio of subsequent passes. (Uneven division). By determining this division coefficient, it is possible to perform pass division at an arbitrary density ratio.

  Reference numeral 801 denotes a first restriction unit that places a restriction to reduce the density ratio of the divided image (first divided image data) in the first pass. The first restriction unit controls the value of the first pass division coefficient K1 that determines the density ratio of the first pass for the pass division table 603 so that adjacent print dots do not overlap. In the second embodiment, K1 = 0.125 is constrained so that the recording duty is a density ratio of 12.5%.

  However, since the degree of dot overlap varies depending on the size of the nozzle arrangement of the recording head 308, the value of the first pass division coefficient K1 is higher or lower than 0.125. When the nozzle arrangement is larger than a predetermined value, the value of the first pass division coefficient K1 is smaller than 0.125, and when the nozzle arrangement is smaller than the predetermined value, the value of K1 is 0. It may be larger than 125. That is, the first pass division coefficient K1 having a value determined by the state of nozzle arrangement is used. Alternatively, the division coefficient K1 may be set so that a single dot of dark ink can be observed by pre-scanning.

  Reference numeral 610_1 denotes a multiplier that calculates the first pass printing density by multiplying the image signal 600 by the first pass division coefficient K1. A multiplier 610_2 multiplies the image signal 600 by the second pass division coefficient K2 to calculate the second pass printing density. Reference numeral 610_3 denotes a multiplier that multiplies the image signal 600 by the third pass division coefficient K3 to calculate the third pass printing density. A multiplier 610_4 calculates the fourth pass printing density by multiplying the image signal 600 by the fourth pass division coefficient K4.

  Reference numeral 650_1 denotes a gradation reduction unit that generates first pass print data from the output of the multiplier 610_1. Reference numeral 650_2 denotes a gradation reduction unit that generates second pass print data from the output of the multiplier 610_2. Reference numeral 650_3 denotes a gradation reduction unit that generates third pass print data from the output of the multiplier 610_3. Reference numeral 650_4 denotes a gradation reduction unit that generates the fourth pass print data from the output of the multiplier 610_4.

  Reference numeral 660_1 denotes a first pass recording image storage unit that temporarily stores the output of the gradation reduction unit 650_1 as a first pass recording image. Reference numeral 660_2 denotes a second pass recording image storage unit that temporarily stores the output of the gradation reduction unit 650_2 as a second pass recording image. Reference numeral 660_3 denotes a third pass recorded image storage unit that temporarily stores the output of the gradation reduction unit 650_3 as a third pass recorded image. Reference numeral 660_4 denotes a fourth pass recorded image storage unit that temporarily stores the output of the gradation reduction unit 650_4 as a fourth pass recorded image.

  Although not shown in FIG. 9B, the image signal of Cc, M, Mm, Y, and K other than C is similarly processed by the pass division circuit 305, the gradation reduction circuit 306, and the print control unit 307. It is processed.

  Next, with reference to FIG. 9B, an example of 4-pass printing that imposes restrictions on the pass division circuit 305 in order to generate a printing dot pattern that is not erroneously detected by the sensor unit 102 in the second embodiment will be described in detail. .

  For the first pass, the image signal 600 is input to the multiplier 610_1, and the first pass printing density is calculated by multiplying the first pass division coefficient K1 read from the pass division table 603. Here, it is assumed that the first pass division coefficient K1 is designated by the first restriction unit 801 as K1 = 0.125, where the recording duty is 12.5%. Next, the output of the multiplier 610_1 is input to the gradation reduction unit 650_1, and the first pass print data is generated. The generated first pass print data is stored as a first pass print image in the first pass print image storage unit 660_1, and then recorded by the print head 308.

  For the second pass, the image signal 600 is input to the multiplier 610_2, and the second pass print density is calculated by multiplying the second pass division coefficient K2 read from the pass division table 603. Here, it is assumed that the second pass division coefficient K2 is specified as K2 = 0.875 / 3, in which the remaining density is equally divided by the remaining number of printing scans of three.

  Although an example in which the remaining density is equally divided is shown here, the division is not necessarily equal and may be unequal.

  Next, the output of the multiplier 610_2 is input to the gradation reduction unit 650_2, and second pass print data is generated. The generated second pass print data is stored in the second pass print image storage unit 660_2 as a second pass print image, and then recorded by the print head 308. At the same time, the recording dot diameter of the first pass that has already been recorded is read by the sensor unit 102 and calculated by the blur detection circuit 311 as the “bleed rate”.

  The switching control unit 312 discriminates the recording medium from the calculated “bleed rate”, and designates a color conversion mode for four-color conversion or six-color conversion for the post-color conversion circuit 304. A switching signal is output. The color conversion post-stage circuit 304 performs color conversion with the specified number of colors. The switching signal output by the switching control unit 312 is held by the switching signal storage unit 313, and color conversion is fixed in subsequent passes.

  For the third pass, the image signal 600 is input to the multiplier 610_3, and the third pass printing density is calculated by multiplying the third pass division coefficient K3 read from the pass division table 603. It is assumed that the third pass division coefficient K3 here is also designated as K3 = 0.875 / 3.

  Next, the output of the multiplier 610_3 is input to the gradation reduction unit 650_3, and third pass print data is generated. The generated third pass print data is stored in the third pass print image storage unit 660_3 as a third pass print image and then recorded by the print head 308. Note that since the recording dot diameter is read by the sensor unit 102 only in the second pass, it is not performed in the third pass.

  For the fourth pass, the image signal 600 is input to the multiplier 610_4, and the fourth pass print density is calculated by multiplying the fourth pass division coefficient K4 read from the pass division table 603. It is assumed that the fourth pass division coefficient K4 here is similarly designated as K4 = 0.875 / 3.

  Next, the output of the multiplier 610_4 is input to the gradation reduction unit 650_4, and the fourth pass print data is generated. The generated fourth pass print data is stored in the fourth pass print image storage unit 660_4 as a fourth pass print image and then recorded by the print head 308. Note that since the recording dot diameter is read by the sensor unit 102 only in the second pass, it is not performed in the fourth pass.

  As described above, according to the configuration example 1 of the second embodiment, by restricting the pass dividing circuit 305, it is possible to generate a single dot of dark ink on the recording medium, and to detect the blur rate. Can be raised.

  Next, as a configuration example 2 of the second embodiment, another configuration for generating a recording dot pattern that is not erroneously detected by the sensor unit 102 will be described. In the configuration example 2, an example of four-pass printing that restricts not only the pass division circuit 305 but also the gradation reduction circuit 306 will be described.

(Configuration example 2)
In Configuration Example 1, an example of generating a recording dot pattern that the sensor unit 102 does not detect erroneously by controlling the overlapping of the recording dots by limiting the recording duty of the first pass to the pass dividing circuit 305. Explained. On the other hand, in the configuration example 2, while restricting the recording duty to a certain degree, and further restricting the gradation reduction circuit 306, the overlapping of the recording dots is minimized. Will be described. With this configuration, a recording dot pattern that is not erroneously detected by the sensor unit 102 is generated.

  FIG. 10A is a block diagram showing a configuration example 2 of the image forming apparatus according to the second embodiment of the present invention.

  In FIG. 10A, a second constraint unit 802 is added in addition to the first constraint unit 801 of FIG. 9A. The second restriction unit 802 imposes restrictions on the dot arrangement of the first pass print data (restriction on the processing contents of the gradation reduction process) for the gradation reduction circuit 306. Specifically, in the gradation reduction process, by controlling the threshold value, control is performed so that a new dot is not generated at a position adjacent to the dot.

  That is, for a position adjacent to a position where dots have already been generated, control is performed such that the threshold value for performing quantization is changed to be high and dot generation is suppressed. On the other hand, in a region where dots are not generated, control is performed so as to promote the generation of dots by changing the threshold value for quantization to a low value. This is because even if the recording duty is 12.5%, if the overlapping of recording dots occurs, the sensor unit 102 in FIG. 2 may erroneously detect, so that the overlapping of recording dots is minimized. In addition, there are restrictions on the arrangement of recording dots. The gradation reduction circuit 306 generates the first pass print data so as to arrange the recording dots according to the control (designated restriction) of the second restriction unit 802.

  FIG. 10B is a block diagram illustrating a detailed configuration of main parts (pass division circuit, gradation reduction circuit, and print control unit) of the image processing unit of the image forming apparatus of FIG. 10A according to the second exemplary embodiment of the present invention.

  In addition, the same reference number is attached about the same component as FIG. 9B, The detail is abbreviate | omitted.

  For the first pass, the image signal 600 is input to the multiplier 610_1, and the first pass printing density is calculated by multiplying the first pass division coefficient K1 read from the pass division table 603. Here, it is assumed that the first pass division coefficient K1 is designated by the first restriction unit 801 as K1 = 0.125, where the recording duty is 12.5%. Next, the output of the multiplier 610_1 is input to the gradation reduction unit 650_1, and the first pass print data is generated.

  At this time, the second constraint unit 802 executes control (constraint) for suppressing the dot generation by changing the quantization threshold value higher than the current value for the adjacent position where the dot has already been generated. . On the other hand, the second constraint unit 802 executes control (constraint) that promotes dot generation by changing the quantization threshold to be lower than the current value in a region where dots are not generated. The first pass print data generated in accordance with this restriction is stored in the first pass print image storage unit 660_1 as the first pass print image, and then recorded by the print head 308.

  The operation of the second pass to the fourth pass is the same as the operation of FIG. 9B.

  As described above, according to the configuration example 2 of the second embodiment, not only the path division circuit 305 but also the gradation reduction circuit 306 is restricted. As a result, it is possible to generate a recording dot pattern in which the overlapping of recording dots is minimized, the detection accuracy of the “bleed rate” is improved, and the recording medium can be more accurately identified.

  Next, as a configuration example 3 of the second embodiment, a configuration in which blur detection is performed on an input image only in a region where the sensor unit 102 does not detect erroneously will be described.

(Configuration example 3)
In the configuration example 1 and the configuration example 2, the dot overlap is controlled by giving a constraint, and as a result, the sensor unit 102 generates a recording dot pattern that is not erroneously detected. On the other hand, in the configuration example 3, a region where there is clearly no overlapping of dots including between colors (region having a low density and close to a single color) is extracted from the input image, and blur detection is performed only for that region. A configuration for preventing erroneous detection of the sensor unit 102 by performing the process will be described.

  FIG. 11 is a flowchart showing a blur detection process in the configuration example 3 of the second embodiment of the present invention.

  This process is executed by the color conversion post-stage circuit 304 of FIG.

  First, the color conversion post-stage circuit 304 senses an input image (step S51). The post-color conversion circuit 304 detects whether or not there is a low density region in the input image (step S52). Here, whether or not there is a low density region is determined by comparing with a certain threshold value when there is a low density region when the input density is smaller than this threshold value. Here, this threshold value can be set in the main body in advance.

  If there is no low density area in the input image (NO in step S52), the process ends. On the other hand, if there is a low density region (YES in step S52), the color conversion post-stage circuit 304 determines whether the low density region is a single color or a region close to a single color (step S53).

  Here, the determination of whether or not the color is monochrome is, for example, dark C density value 50, light C density value 0, dark M density value 0, light M density value 0, Y density value 0, and K density value 0. If there is a density value for only one color, it is determined as a single color. The determination of whether or not the color is close to a single color is made, for example, as a dark C density value 50, a light C density value 5, a dark M density value 5, a light M density value 5, a Y density value 5, and a K density value 5. Except for one color, the other colors are determined to be close to a single color when the density value is close to 0 (within a predetermined range from the density value 0). These determination criteria can be set in the main body in advance.

  Thus, in the input image data, the density is a predetermined value A or less, and the density of each of the other color components is a predetermined value B or less (A >> B) with respect to the density of the target color component Whether image data exists is detected. When such partial image data is detected, the bleeding rate is detected with respect to the image area formed on the recording medium by the partial image data.

  If the low density region is not a single color or a region close to a single color (NO in step S53), the process ends. On the other hand, if the low density region is a single color or a region close to a single color (YES in step S53), the color conversion post-stage circuit 304 holds position information where the region is recorded (step S54). Then, after the area is recorded, the color conversion post-stage circuit 304 executes the “bleed rate” detection process by the blur detection circuit 311 only for the area (step S55).

  As described above, according to the configuration example 3 of the second embodiment, the input image is sensed, and an area where there is clearly no dot overlap including between colors is extracted. "Rate" detection processing is executed. As a result, the sensor unit can execute the “bleed rate” detection process for an area where there is no overlapping of dots, and it is possible to prevent erroneous detection of the sensor unit.

<Embodiment 3>
In the third embodiment, a density correction circuit and a density conversion circuit are added to the image processing forming apparatus, and the sensor unit 102 reads not only the recording dot diameter but also the density of the recorded image from the recording medium. A configuration for performing density correction by recording scanning will be described.

  FIG. 12 is a block diagram showing the configuration of the image forming apparatus according to the third embodiment of the present invention.

  In particular, in FIG. 12, a density correction circuit 1002 and a density conversion circuit 1001 are configured with respect to the configuration of the image forming apparatus of FIG. Here, the same components as those in FIG. 3 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The color conversion post-stage circuit 304 initially starts with four-color conversion (R′G′B ′ → CMYK) using only dark ink (at this time, data “0” is present in Cc and Mm in the figure). ). Then, the color conversion post-stage circuit 304 performs a color conversion process for switching from the four color conversion to the six color conversion including dark and light inks (R′G′B ′ → CCcMMmYK) according to a command from the switching control unit 312.

  The density conversion circuit 1001 converts the detection signal detected by the sensor unit 102 into a recording density. The density correction circuit 1002 compares the detected recording density with the calculated target density, and performs density correction on the image data after the second pass with the difference.

  FIG. 13 is a block diagram illustrating a detailed configuration of main parts (pass division circuit, density correction circuit, gradation reduction circuit, and print control unit) of the image processing unit of the image forming apparatus according to the third exemplary embodiment of the present invention.

  In FIG. 13, a density conversion circuit 1001 converts a detection signal detected by the sensor unit 102 into a recording density.

  615_1 is the first pass printing density ratio (K1). Reference numeral 615_2 denotes a total print density ratio (K1 + K2) of the first pass print density ratio (K1) and the second pass print density ratio (K2). 605_3 is a total print density ratio (K1 + K2 + K3) of the first pass print density ratio to the third pass print density ratio (K1 to K3).

  Reference numeral 620_1 denotes a multiplier that calculates a print target density for the first pass. Reference numeral 620_2 denotes a multiplier that calculates the total print target density in the first pass + second pass. Reference numeral 620_3 denotes a multiplier that calculates the total print target density in the first pass + second pass + third pass.

  Reference numeral 630_1 denotes an adder that calculates the difference between the total print target density in the first pass + second pass and the print density up to the first pass detected by the sensor unit 102. Reference numeral 630_2 denotes an adder that calculates the difference between the total print target density in the first pass + second pass + third pass and the print density up to the second pass detected by the sensor unit 102. Reference numeral 630_3 denotes an adder that calculates a difference between the print target density of the image signal 600 and the print density up to the third pass detected by the sensor unit 102.

  Next, referring to FIG. 13, in the third embodiment, the density correction circuit 1002 reads not only the recording dot diameter but also the recording density of the recorded image by the sensor unit 102, and the density in the subsequent recording scanning according to the read density. An example of 4-pass printing for performing correction will be described in detail.

  For the first pass, the image signal 600 is input to the multiplier 620_1, and the first pass print density is calculated by multiplying the first pass print density ratio (K1) read from the pass division table 603. Next, the output of the multiplier 620_1 is input to the gradation reduction unit 650_1, and the first pass print data is generated. The generated first pass print data is stored as a first pass print image in the first pass print image storage unit 660_1, and then recorded by the print head 308.

  For the second pass, the image signal 600 is input to the multiplier 620_2, and the second pass printing density ratio (K1 + K2) read from the pass division table 603 is multiplied to print the total of the first pass and the second pass. A target concentration is calculated. At the same time, the recording density up to the first pass is read while the sensor unit 102 reads the recording dot diameter of the first pass that has already been recorded. The read recording dot diameter is calculated as a “bleed rate” by the blur detection circuit 311.

  The switching control unit 312 discriminates the recording medium from the calculated “bleed rate”, and designates a color conversion mode for four-color conversion or six-color conversion for the post-color conversion circuit 304. A switching signal is output. The color conversion post-stage circuit 304 performs color conversion with the specified number of colors. The switching signal output by the switching control unit 312 is held by the switching signal storage unit 313, and color conversion is fixed in subsequent passes.

  On the other hand, the read recording density up to the first pass is input to the adder 630_1, and the difference between the total printing target density of the first pass + second pass and the recording density up to the first pass detected by the sensor unit 102. Calculate Next, the output of the adder 630_1 is input to the gradation reduction unit 650_2, and second pass print data is generated. The generated second pass print data is stored in the second pass print image storage unit 660_2 as a second pass print image, and then recorded by the print head 308.

  For the third pass, the image signal 600 is input to the multiplier 620_3 and multiplied by the third pass printing density ratio (K1 + K2 + K3) read from the pass division table 603, so that the first pass + the second pass + the third pass. The total print target density is calculated. At the same time, the recording density up to the second pass is read by the sensor unit 102. Note that since the recording dot diameter is read only in the second pass and not in the third pass, only the recording density is read here.

  The read recording density up to the second pass is input to the adder 630_2, and the total print target density of the first pass + second pass + third pass and the print density up to the second pass detected by the sensor unit 102 are obtained. Calculate the difference between Next, the output of the adder 630_2 is input to the gradation reduction unit 650_3, and third pass print data is generated. The generated third print data is stored as a third pass recording image in the third pass recording image storage unit 660_3 and then recorded by the recording head 308.

  With respect to the fourth pass, the image signal 600 is equivalent to the overall print target density, and therefore it is not necessary to calculate the print target density. At the same time, the sensor unit 102 reads the recording density up to the third pass. Note that since the recording dot diameter is read only in the second pass and not in the fourth pass, only the recording density is read here.

  The read recording density up to the third pass is input to the adder 630_3, and the difference between the image signal 600 and the recording density up to the third pass detected by the sensor unit 102 is calculated. Next, the output of the adder 630_3 is input to the gradation reduction unit 650_4, and fourth pass print data is generated. The generated fourth pass print data is stored in the fourth pass print image storage unit 660_4 as a fourth pass print image and then recorded by the print head 308.

  In the third embodiment, since the density on the recording medium is fed back, control different from the first and second embodiments is possible.

  That is, in the first and second embodiments, color conversion is performed as a four-color output (no light ink) until the recording medium determination is finalized. On the other hand, in the third embodiment, until the determination of the recording medium is confirmed, color conversion is performed as six-color output, and the density of the light ink is forced to zero. Thereafter, when it is determined that the output is four colors, the color conversion is switched to the four-color output mode, and when it is determined that the output is six colors, the density of the light ink is forcibly kept in the six-color output mode. The control to set to 0 is canceled and normal 6-color output is obtained. As a result, it is possible to prevent dark ink from entering the highlight area and to minimize image quality deterioration due to switching.

  As described above, according to the third embodiment, not only the recording dot diameter but also the density of the recording image is read, and the density correction is performed in the subsequent recording scanning according to the reading density. As a result, in addition to the effects described in the first and second embodiments, not only the density ink distribution control suitable for the recording medium, but also multi-pass recording suitable for the recording medium is possible from the viewpoint of the recording density.

  Although the embodiment has been described in detail above, the present invention can take an embodiment as a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to an apparatus composed of a single device.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowchart shown in the drawing) that realizes the functions of the above-described embodiments is directly or remotely supplied to a system or apparatus. In addition, this includes a case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  Examples of the recording medium for supplying the program include a floppy (registered trademark) disk, a hard disk, and an optical disk. Further, as a recording medium, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD-R), etc. is there.

  As another program supply method, a browser on a client computer is used to connect to an Internet home page. Then, the computer program itself of the present invention or a compressed file including an automatic installation function can be downloaded from a homepage of the connection destination to a recording medium such as a hard disk. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. Let me. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Further, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can be realized by the processing.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instructions of the program, and the functions of the above-described embodiments are realized by the processing.

It is a figure which shows the recording head part of the inkjet recording device of Embodiment 1 of this invention. It is a figure which shows a mode that the sensor part of Embodiment 1 of this invention reads the recording dot diameter of the image recorded on the recording medium. 1 is a block diagram illustrating a configuration of an image forming apparatus according to a first exemplary embodiment of the present invention. FIG. 3 is a diagram illustrating the shape of a recording dot on each recording medium when recording is performed by ejecting ink from the recording head to two recording media having different ink absorbability according to the first exemplary embodiment of the present invention. It is a flowchart which shows the "bleeding rate" detection process which the blur detection circuit of Embodiment 1 of this invention performs. It is a flowchart which shows the color conversion switching control process which the switching control part of Embodiment 1 of this invention performs. It is a figure which shows the dot profile which is the characteristic of the dot diameter of Embodiment 1 of this invention. It is an image figure which shows arrangement | positioning of the recording dot on the recording medium of Embodiment 2 of this invention. It is a block diagram which shows the structural example 1 of the image forming apparatus of Embodiment 2 of this invention. FIG. 9B is a block diagram illustrating a detailed configuration of main parts (pass division circuit, gradation reduction circuit, and print control unit) of the image processing unit of the image forming apparatus of FIG. 9A according to the second exemplary embodiment of the present invention. It is a block diagram which shows the structural example 2 of the image forming apparatus of Embodiment 2 of this invention. FIG. 10B is a block diagram illustrating a detailed configuration of main parts (pass division circuit, gradation reduction circuit, and print control unit) of the image processing unit of the image forming apparatus in FIG. 10A according to the second exemplary embodiment of the present invention. It is a flowchart which shows the blur detection process in the structural example 3 of Embodiment 2 of this invention. It is a block diagram which shows the structure of the image forming apparatus of Embodiment 3 of this invention. FIG. 10 is a block diagram illustrating a detailed configuration of main parts (a pass division circuit, a density correction circuit, a gradation reduction circuit, and a print control unit) of an image processing unit of an image forming apparatus according to a third exemplary embodiment of the present invention. It is a figure which shows the recording head part of the conventional inkjet printer. It is a figure for demonstrating the multipass printing by the printer using the recording head shown in FIG. It is a figure which shows the process of the conventional inkjet recording device. It is a graph which shows the density | concentration with respect to the ink amount on a recording medium. It is a figure which shows the method currently disclosed by patent document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Recording head part 102 Sensor part 201 Recorded image 202 Recording medium 301 Image data recording apparatus 302 γ conversion circuit 303 Color conversion pre-stage circuit 304 Color conversion post-stage circuit 305 Path division circuit 306 Low gradation circuit 307 Print control unit 308 Recording head 311 Smudge detection circuit 312 switching control unit

Claims (11)

An image forming apparatus for forming an image in the same area on a recording medium by a plurality of recording scans of a recording head that discharges a plurality of recording agents having different densities,
Input means for inputting image data;
A first color conversion process for color conversion to color component image data corresponding to a recording agent having a high density among the plurality of recording agents having different densities, and colors corresponding to the recording agents of the plurality of recording agents having different densities. Color conversion means for color-converting image data input by the input means using any of the second color conversion processing for color conversion to component image data;
Wherein a plurality of times of printing scan, the printing scan of the recording head prior to acquiring the information indicating the absorption rate of said recording agents definitive on the recording medium acquisition means,
Based on the absorption rate of the recording agent acquired by the acquisition unit, the first color conversion process is selected when the absorption rate is low, and the second color conversion process is selected when the absorption rate is high. An image forming apparatus comprising: a switching control unit to be executed by a color conversion unit. The acquisition means acquires information indicating a dot diameter of a recording dot formed on the recording medium, and the recording medium of the recording dot formed on the recording medium based on a dot diameter and a reference dot diameter Calculate the bleeding rate indicating an index for determining the absorption rate of the recording agent above ,
The switching control unit selects the first color conversion process when the bleeding rate is equal to or greater than a first threshold value, and causes the color conversion unit to execute the blurring rate, and when the bleeding rate is smaller than the first threshold value, The image forming apparatus according to claim 1, wherein a second color conversion process is selected and executed by the color conversion unit. The switching control unit selects the first color conversion process and causes the color conversion unit to execute until a recording dot having a bleeding rate smaller than the first threshold is acquired by the acquisition unit. The image forming apparatus according to claim 2. Said switching control means, to said bleeding rate is the number of the first threshold value is smaller than the recording dot exceeds a second threshold, select the first color conversion process, characterized in that to be executed by the color converting means The image forming apparatus according to claim 3. Dividing means for dividing the color component image data generated by the color conversion means into divided image data corresponding to each of the plurality of recording scans;
Of the plurality of recording scans, the dividing unit does not overlap the recording dots formed on the recording medium based on the first divided image data corresponding to the first recording scan. The image forming apparatus according to claim 3, further comprising: a first restriction unit that restricts a division ratio for generating image data. A gradation reducing means for reducing the gradation of the divided image data divided by the dividing means;
Recording dots formed on the recording medium based on the first divided image data whose gradation is reduced by the gradation-reducing means, corresponding to the first recording scan among the plurality of recording scans However, the processing contents of the gradation reduction process for generating the first divided image data with the gradation reduced in the gradation reducing means are restricted so that adjacent recording dots are not overlapped. The image forming apparatus according to claim 5, further comprising: a second restriction unit. The acquisition means includes a portion of the input image data in which the density is a predetermined value A or less and the density of each of the other color components is a predetermined value B or less (A> B) with respect to the density of the target color component. A determination means for determining whether image data exists,
The characteristic of the recording dot of the image area formed on the recording medium is acquired by the partial image data when the partial image data exists as a result of the determination by the determining means. The image forming apparatus described in 1. The acquisition unit further acquires a recording density of an image formed on the recording medium by a recording scan of the recording head preceding among the plurality of recording scans,
Based on the recording density acquired by the acquisition means, the image processing apparatus further comprises a correcting means for correcting the density of the color component image data used for the recording scanning of the recording head after the recording scanning of the plurality of times. The image forming apparatus according to claim 2 . The switching control means performs the same color conversion as when the first color conversion process is selected by setting the density of the recording agent having a low density in the second color conversion process to 0 until the blur rate is calculated. processing is executed on the color conversion processing means, the calculated the bleeding rate, that said bleeding ratio is to 0 the concentration of low concentration recording agent in the second color conversion processing is equal to or greater than the first threshold value The image forming apparatus according to claim 8 , wherein the second color conversion processing is executed by the color conversion unit. A control method of an image forming apparatus for forming an image in the same area on a recording medium by a plurality of recording scans of a recording head that discharges a plurality of recording agents having different densities,
An input process for inputting image data;
A first color conversion process for color conversion to color component image data corresponding to a recording agent having a high density among the plurality of recording agents having different densities, and colors corresponding to the recording agents of the plurality of recording agents having different densities. A color conversion step for color-converting the image data input in the input step using any one of the second color conversion processes for color conversion to component image data;
Among the plurality of recording scans, an acquisition step of the printing scan of the recording head prior to acquiring the information indicating the absorption rate of said recording agents definitive on the recording medium,
Based on the absorption rate of the recording agent acquired in the acquisition step, the first color conversion process is selected when the absorption rate is low, and the second color conversion process is selected when the absorption rate is high. And a switching control step for causing the color conversion step to be performed. By executing so incorporated read into a computer, a computer program for causing the computer to function as the image forming apparatus according to any one of claims 1 to 9.

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