JP2004074509A - Image processor and processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor and an image processing method in which a deterioration in image quality can be prevented by realizing color shift correction of less than one pixel in addition to average color shift correction on all scanning line. <P>SOLUTION: In an image processor connectable with a printer engine 106 printing a color image, a color shift processing section 146 measures color shift information of an inputted color image and corrects the color shift information thus measured. A color transforming section 144 transforms the inputted color image into print color data corresponding to the toner color of the printer engine 106. Furthermore, a gray scale correcting section 147 and a dither processing section 151 transform the gray scale of print color data. In the image processor, a latent image is formed from the print color data transformed by gray scale and corrected with reference to corrected color shift information. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and method for a color image forming apparatus that forms a color image by performing pulse width modulation processing for each color component data and performing line scanning.
[0002]
[Prior art]
As an output device of image data stored in a computer, an information recording device using an electrophotographic method, such as a laser beam printer (LBP), is widely used. These information recording devices have many advantages such as high quality printing results, quietness and high speed, and are one of the factors that rapidly expand the field of desktop publishing. In addition, the high performance of the host computer and the controller, which is the image generation unit of the printer, makes it possible to easily handle color images.Electrophotographic color printers have also been developed. However, printing of color images is also becoming popular.
[0003]
In a color printer, a color conversion parameter is set so that a photographic image input from an image scanner, a digital camera, or the like, or image data such as a color document created by an application on a host computer is matched to a color output characteristic unique to the printer. The image data is converted by the color conversion processing using. As the color conversion parameters, information in a matrix or look-up table (LUT) format is used.
[0004]
Normally, in an electrophotographic color printer, a color shift occurs in the main scanning direction for each color. Therefore, a latent image of a color shift test pattern is formed on a transfer body such as an intermediate transfer body, and a correction value is calculated from a value read by a sensor or the like. In addition, adjustment of a color shift for correcting a writing position is performed.
[0005]
As described above, when adjusting the color misregistration in the main scanning direction that occurs due to the characteristics of the color laser beam printer, a certain amount of correction is performed by adjusting the writing position of the main scanning using the correction value obtained from the test pattern. It is possible.
[0006]
[Problems to be solved by the invention]
However, depending on the accuracy of the surface uniformity of the transfer body, such as a belt, the writing position is shifted for each scanning line, so that the color shift in the main scanning direction cannot be completely corrected. There has been a problem that color misregistration occurs in the line, which causes deterioration of image quality.
[0007]
The present invention has been made in view of such circumstances, and prevents image quality deterioration by realizing color shift correction of less than one pixel with respect to average color shift amount correction over all scanning lines. It is an object of the present invention to provide an image processing apparatus and method capable of performing the above-described operations.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention provides an image processing apparatus for a color image forming apparatus that forms a color image by performing pulse width modulation processing for each color component data and performing line scanning. And a setting means for setting a pulse width growth pattern of the pulse width modulation process in accordance with the color shift information.
[0009]
Further, in the image warping apparatus according to the present invention, the color misregistration processing unit is formed by a patch pattern generation unit for generating an image of a predetermined patch pattern, and a patch pattern generated by the patch pattern generation unit. A color shift information generation unit configured to measure a color shift amount in the main scanning direction from the image and generate the color shift information.
[0010]
Further, the image processing apparatus according to the present invention includes: an input unit for inputting color component data constituting a color image; a pseudo gradation processing unit for converting the color component data into pseudo gradation data; Pulse width modulation means for pulse width modulating the color component data processed by the means with the pulse width growth pattern set by the setting means.
[0011]
Still further, the image processing apparatus according to the present invention is characterized in that the pulse width modulation means includes a plurality of pattern tables having different pulse width growth patterns, and selects the plurality of pattern tables according to the color misregistration information. And
[0012]
Still further, the image processing apparatus according to the present invention is characterized in that the plurality of pattern tables have different pulse width growth patterns within one pixel.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a color printer including an image processing apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiment, an example in which the present invention is applied to a 600 dpi color laser beam printer will be described. However, the present invention is not limited to this case, and can be applied to a color image printing apparatus such as a color printer or a color facsimile apparatus having an arbitrary recording density.
[0014]
<First embodiment>
FIG. 1 is a configuration diagram showing an outline of a color image printing system including a color laser beam printer 102 according to the first embodiment of the present invention. As shown in FIG. 1, the color image printing system according to the present embodiment is configured by connecting a host computer 101 and a color laser beam printer 102 via a network 100.
[0015]
Here, the network 100 can be generally realized using Ethernet (registered trademark). For example, information transmission and data transfer between connected units can be performed by a protocol such as TCP / IP using a physical cable such as 10BaseT. Further, the host computer 101 sends to the color laser beam printer 102 print information necessary for performing print processing such as color information, character information, graphic information, an image image, and the number of prints. The color laser beam printer 102 has a function of performing a printing process based on print information received from the host computer 101 via the network 100.
[0016]
Next, the configuration of the color laser beam printer 102 according to the present embodiment will be described. The color laser beam printer 102 includes a network interface (hereinafter, referred to as “network I / F”) 103, an image processing unit 104, a control unit 105, a printer engine 106, a CPU 107, a ROM 108, and a RAM 109.
[0017]
Here, the image processing unit 104 and the control unit 105 are connected to each other via a bus (not shown), and are connected to the network 100 via the network I / F 103. Further, the image processing unit 104 is connected to a printer engine 106 that forms an actual image based on the image signal transmitted from the image processing unit 104.
[0018]
On the other hand, the control unit 105 controls the operation of the entire color laser beam imprinter 102. This control can be performed by the CPU 107 transmitting a control signal for determining and controlling various processes to the control unit 105 in accordance with the control program 108a stored in the ROM 108. The RAM 109 is used as a work area 109a for storing data for the CPU 107 to perform each control.
[0019]
FIG. 2 is a block diagram showing a detailed configuration of the image processing unit 104 in the color laser beam printer 102. Next, the operation of the image processing unit 104 will be described with reference to FIG.
[0020]
2, a reception buffer 141 holds print information input via the network I / F 103. The color conversion mode setting unit 142 stores color conversion parameters corresponding to color conversion modes such as standard colors, high gloss colors, low gloss colors, and high definition colors input from the host computer 101 from the color conversion parameter holding unit 143. The user selects and creates and stores the color conversion table 145. The color conversion parameter holding unit 143 holds a plurality of color conversion parameters corresponding to the color conversion mode, as described above.
[0021]
The color conversion unit 144 converts the print information in RGB format of the image data input from the host computer 101 into print information in CMYK format by performing interpolation processing with reference to the color conversion table 145. The color misregistration amount processing unit 146 sets a color misregistration amount with respect to the main scanning information of the print information held in the reception buffer 141, and performs a PWM (Pulse Width Modulation: pulse width modulation) corresponding to the set color misregistration amount. ) Set the pattern in the PWM pattern table 158. The details of the color shift amount processing unit 146 will be described later.
[0022]
The density correction processing unit 147 performs a correction process on the print information in the CMYK format converted by the color conversion unit 144 such that the density characteristics maintain linearity using the density correction table 148.
[0023]
The matrix setting unit 149 selects a dither parameter corresponding to a dither mode such as 4-bit dither, 2-bit dither, or 1-bit dither input from the host computer 101 from the dither parameter holding unit 150, and creates a dither table 152. Store. Here, the dither parameter holding unit 150 holds a plurality of dither parameters corresponding to the above-described dither mode. Then, the dither processing unit 151 performs a comparison operation on the CMYK format print information corrected by the density correction processing unit 147 with reference to the dither table 152 to obtain print information of the number of gradations corresponding to the dither mode. Convert.
[0024]
Next, the object generator 153 converts information (page description language) such as image data input from the host computer 101 into an object. In the present embodiment, the image data is converted into a CMYK format object converted by the processing in the color conversion unit 144, the density correction processing unit 147, and the dither processing unit 151. Then, the object for one page converted by the object generation unit 153 is stored in the object buffer 154.
[0025]
Further, the rendering unit 155 performs a rendering process based on the object for one page stored in the object buffer 154, and converts it into bitmap data to be rendered. The band buffer 156 stores the bitmap data generated by the rendering unit 155, and sends the data to the PWM processing unit 157.
[0026]
The PWM processing unit 157 converts the bitmap data generated by the rendering unit 155 based on the pulse width modulation table set in the PWM pattern table 158 with a pulse width corresponding to the irradiation time of laser exposure. Modulation processing is performed, and the result is transmitted to the printer engine 106.
[0027]
That is, the present embodiment relates to an image processing apparatus connectable to the printer engine 106 that prints a color image, in which the color shift amount processing unit 146 measures color shift information of an input color image, and Correct the information. Further, the color conversion unit 144 converts the input color image into print color data corresponding to the toner color of the printer engine 106. Further, the density correction processing unit 147 and the dither processing unit 151 convert the gradation of the print color data. Further, the image processing apparatus forms a latent image from the print color data after the gradation conversion, and corrects the latent image with reference to the corrected color shift information.
[0028]
In addition, the image processing apparatus according to the present embodiment includes a density correction processing unit 147 that converts print color data into linear color density data having linearity, and a dither processing unit 151 that converts linear color density data into pseudo gradation data. Wherein the color shift amount processing unit corrects the pulse width modulation pattern table in which the color shift information and the pulse width modulation pattern correspond to each other based on the color shift information.
[0029]
Next, the operation of the image processing unit 104 in the color laser beam printer 102 having the above configuration will be described in detail. FIG. 3 is a flowchart for explaining the operation of the image processing unit 104 in the color laser beam printer 102. Note that the control program for realizing the series of processes shown in the flowchart of FIG. 3 is stored in the ROM 108 and executed by the CPU 107 as described above.
[0030]
As shown in the flowchart of FIG. 3, first, as the initialization processing of the color laser beam printer 102, the initialization of the printer status and the initialization of the buffer are performed (step S301). Next, print data is received by the network I / F 103 from the host computer 101 via the network 100 (step S302). Then, the received print data is held in the reception buffer 141 (step S303).
[0031]
Next, data for one processing unit is fetched from the reception buffer 141 (step S304), and then it is determined whether or not all data has been fetched (step S305). As a result, if it is determined that all the data has been extracted (Yes), the printing process ends. On the other hand, if it is determined that all data has not been extracted (No), it is next determined whether or not data processing for one page has been completed (step S306).
[0032]
If it is determined in step S306 that one page of data has been completed (Yes), rendering processing is performed by the rendering unit 155 based on the object held in the object buffer 154 (step S321). Next, pulse width modulation processing is performed on the bitmap image by the PWM processing unit 157 (step S322). Further, a printing process for transmitting the data to the printer engine 106 and performing printing on the paper is executed (step S323), and the process returns to step S304.
[0033]
On the other hand, if it is determined in step 306 that the data processing for one page has not been completed (No), then it is determined whether the print data is color-related data such as color information or a color image image. (Step S307). As a result, if the print data is color-related data (Yes), the color conversion unit 144 converts the color data in the RGB format into the color data in the CMYK format by performing an interpolation operation with reference to the color conversion table 145 ( Step S308). Further, the density correction processing section 147 performs density correction of the density level using the density correction table 148 (step S309).
[0034]
Next, the dither processing unit 151 performs a comparison operation with the dither table 152, and the density-corrected data is converted into dither-processed color data (step S310). Further, an object is generated by the object generation unit 153 (step S311), stored in the object buffer 154 (step S312), and returns to step S304.
[0035]
On the other hand, if it is determined in step S307 that the print data is not color-related data (No), then it is determined whether the print data is color conversion mode data (step S313). As a result, if the print data is the color conversion mode data (Yes), the color conversion mode setting unit 142 creates a color conversion table 145 based on the color conversion parameters corresponding to the color conversion mode (step S314), and proceeds to step S304. Return.
[0036]
On the other hand, if it is determined in step S313 that the print data is not the color conversion mode data (No), then it is determined whether the print data is the dither mode data (step S315). As a result, if the print data is dither mode data (Yes), the matrix setting unit 149 creates a dither table 152 based on the dither parameters corresponding to the dither mode (step S316), and returns to step S304.
[0037]
On the other hand, if it is determined in step S315 that the print data is not dither mode data (No), then it is determined whether the print data is PWM mode data (step S317). As a result, if the print data is PWM mode data (Yes), a PWM pattern corresponding to the color shift amount set by the color shift amount processing unit 146 is set in the PWM pattern table (step S318), and the process returns to step S304. .
[0038]
On the other hand, if it is determined in step S317 that the print data is not the PWM mode data (No), then it is determined whether the print data is mask data such as a character or a graphic (step S319). As a result, when it is determined that the print data is the mask data (Yes), an object of the mask data is created (step S311) and stored in the object buffer 154 (step S312). On the other hand, if it is determined in step S319 that the print data is not mask data (No), print data processing according to the type of data is performed (step S320), and the process returns to step S304.
[0039]
FIG. 4 is a block diagram illustrating a detailed configuration of the color shift amount processing unit 146 in the image processing unit 104 according to the present embodiment. Next, the operation of the color misregistration amount processing unit 146 will be described in detail with reference to FIG. As shown in FIG. 4, the color shift amount processing unit 146 includes a color shift pattern measurement unit 401, a color shift amount calculation unit 402, a line memory reading unit 403, a line memory 404, and a color shift pattern generation unit 405. .
[0040]
The color misregistration pattern measurement unit 401 reads the color misregistration pattern created by the color misregistration pattern generation unit 405 and latently imaged on the transfer body on the printer engine 106 by a reading element such as a sensor. Further, the color misregistration amount calculation unit 402 calculates the color misregistration amount for each of the CMYK colors from the sensor values read by the color misregistration pattern measurement unit 401.
[0041]
The line memory reading unit 403 reads color shift information of the corresponding scanning line from the line memory 404 from the main scanning information of the print information stored in the reception buffer 141. In the line memory 404, the color shift amount calculated by the color shift amount calculation unit 402 is stored for each scanning line for each of CMYK colors. The color misregistration pattern generation unit 405 is controlled by the control unit 105, generates a test pattern for measuring a color misregistration amount, and transmits data to the PWM processing unit.
[0042]
Next, the operation of the color misregistration amount processing unit 146 in the color laser beam printer 102 according to the present embodiment will be described in detail. FIG. 5 is a flowchart for explaining the operation of the color misregistration amount processing unit 146 in the color laser beam printer 102. First, a color misregistration pattern is formed on the intermediate transfer body (not shown) by the color misregistration pattern generation unit 405 (step S501). Next, the color misregistration pattern measuring unit 401 measures a color misregistration pattern using a sensor (not shown) (Step S502). Then, the color misregistration pattern measurement unit 401 receives the color misregistration value measured by the sensor (Step S503).
[0043]
Next, the color shift amount calculation unit 402 calculates a color shift amount corresponding to the color shift value (step S504). Further, the amount of color misregistration is set in the line memory 404 (step S505), and the process ends. Here, FIG. 6 is a diagram illustrating an example in which the color shift amount processed by the color shift processing unit 146 is set in the line memory. In FIG. 6, the color misregistration amount is set in units of ± 1/8 pixel with K as a reference color (that is, 0).
[0044]
Next, the operation of the PWM processing unit 157 in the color laser beam printer 102 according to the present embodiment will be described in detail. In the present embodiment, the PWM processing uses a pattern growth table and digitally controls the amount of laser emission according to each pattern.
[0045]
FIG. 7 is a flowchart for explaining the operation of the PWM processing unit 157 in the color laser beam printer 102. As shown in FIG. 7, first, the stored bitmap data is extracted from the band buffer 156 (step S701). Then, it is determined whether all data for one page has been processed (step S702).
[0046]
As a result, when it is determined that the processing for one page is completed (Yes), the processing is completed. On the other hand, if it is determined that the data for one page has not been completely processed (No), it is next determined whether or not the data for one scanning line has been processed (step S703).
[0047]
As a result, if it is determined that the data processing for one scanning line has been completed (Yes), the process returns to step S702. On the other hand, if it is determined that data for one scanning line has not been processed (No), it is next determined whether or not data for one plane of each of the CMYK planes has been processed (step S704).
[0048]
As a result, if it is determined that the data processing for one plane has been completed (Yes), the process returns to step S703. On the other hand, if it is determined that the data for one plane has not been processed (No), then the color shift amount corresponding to the processing scanning line of the plane for which data processing is performed from the line memory 404 in the color shift amount processing unit 146. Is read (step S705). Next, it is determined whether or not the color shift amount is 0 (step S706).
[0049]
As a result, when it is determined that the color misregistration amount is 0 (Yes), the corresponding center-grown PWM pattern is stored in the PWM pattern table 158 (step S707). Next, laser irradiation is performed in accordance with the stored PWM growth pattern (step S708), and the process returns to step S704.
[0050]
On the other hand, if it is determined in step S706 that the color shift amount is not 0 (No), then it is determined whether the color shift amount is smaller than 0 (step S709). As a result, when it is determined that the color misregistration amount is smaller than 0 (Yes), the corresponding right-growth PWM pattern is stored in the PWM pattern table 158 (step S710). Then, after executing the process of step S708 as described above, the process returns to step S704. On the other hand, when it is determined in step S709 that the color misregistration amount is not smaller than 0 (No), the corresponding left-growth PWM pattern is stored in the PWM pattern table 158 (step S711), and after executing the processing in step S708, It returns to step S704.
[0051]
That is, in the image processing apparatus according to the present embodiment, the color shift amount processing unit 146 includes a color shift pattern generation unit 405 that causes the printer engine 106 to form a predetermined patch pattern latent image, A color shift amount calculating unit that measures a color shift amount from the pattern latent image and generates color shift information of each scanning line from the measured color shift amount.
[0052]
Further, the present embodiment is characterized in that the PWM processing unit 157 switches a plurality of pulse width modulation patterns included in the PWM pattern table 158.
[0053]
Further, in the present embodiment, the pulse width modulation pattern based on the result obtained from the color misregistration pattern measurement unit 401 is set in the PWM pattern table 158, and the PWM processing unit 157 refers to the set PWM pattern table 158. In addition, pulse width modulation processing is performed on the pseudo gradation data.
[0054]
Furthermore, the present embodiment is characterized in that the PWM pattern table 158 can correspond to a latent image composed of predetermined multi-tone values.
[0055]
FIG. 8 is a diagram illustrating an example of a PWM pattern table set by the color misregistration amount processing unit 146 according to the present embodiment. In FIG. 8, the table on the left side shows the set values of the PWM pattern table. FIG. 8 shows an example in which one pattern table is divided into eight pixels per pixel and has a data value of 10-bit width capable of expressing five gradations. A color shift amount setting flag is set for B9 and B8, and a PWM is set for B7 to B0. This is the pattern data assigned.
[0056]
On the other hand, a schematic diagram of the set PWM pattern table is shown on the right side of FIG. 8, and shows an example of a central growth pattern, a right growth pattern, and a left growth pattern, respectively.
[0057]
FIG. 9 is a schematic diagram of a print output corresponding to each print ratio in a stage where the color misregistration amount processing is not performed. FIG. 10 is a schematic diagram of a print output corresponding to each print ratio after the color misregistration amount processing.
[0058]
<Other embodiments>
In the above-described embodiment, the input data is RGB data and the output data is CMYK data. However, the present invention is also applicable to any color space expression such as L * a * b * and XYZ.
[0059]
In the above-described embodiment, the PWM growth pattern table has five gradations. However, the table can be applied to a table with an arbitrary number of gradations.
[0060]
Further, in the above-described embodiment, the PWM growth patterns are center growth, right growth, and left growth, but the present invention can be applied to any growth pattern.
[0061]
Furthermore, in the above-described embodiment, the PWM processing is performed by digital control using a pattern table, but may be performed by another control method.
[0062]
Note that the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but a device including one device (for example, a copying machine, a facsimile machine, etc.). May be applied.
[0063]
Further, an object of the present invention is to supply a recording medium (or a recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or an apparatus, and a computer (or a CPU or a CPU) of the system or the apparatus. Needless to say, the present invention can also be achieved by the MPU) reading and executing the program code stored in the recording medium. In this case, the program code itself read from the recording medium implements the functions of the above-described embodiment, and the recording medium on which the program code is recorded constitutes the present invention. When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a part or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing.
[0064]
Further, after the program code read from the recording medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0065]
When the present invention is applied to the recording medium, the recording medium stores program codes corresponding to the flowcharts described above.
[0066]
【The invention's effect】
As described above, according to the present invention, it is possible to further realize the color shift correction of less than one pixel with respect to the average color shift amount correction over all the scanning lines.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an outline of a color laser beam printer 102 according to a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a detailed configuration of an image processing unit 104 in the color laser beam printer 102.
FIG. 3 is a flowchart illustrating an operation of an image processing unit 104 in the color laser beam printer 102.
FIG. 4 is a block diagram illustrating a detailed configuration of a color misregistration amount processing unit 146 in the image processing unit 104.
FIG. 5 is a flowchart for explaining the operation of a color misregistration amount processing unit 146 in the color laser beam printer 102.
FIG. 6 is a diagram illustrating an example of a case where a color shift amount processed by a color shift processing unit 146 is set in a line memory;
FIG. 7 is a flowchart illustrating an operation of a PWM processing unit 157 in the color laser beam printer 102.
FIG. 8 is a diagram showing an example of a PWM pattern table set by a color misregistration amount processing unit 146 according to the embodiment.
FIG. 9 is a schematic diagram of a print output corresponding to each print ratio in a stage where the color misregistration amount processing is not performed.
FIG. 10 is a schematic diagram of a print output corresponding to each print ratio after the color shift amount processing.
[Explanation of symbols]
100 networks
101 Host computer
102 color laser beam printer
103 Network Interface
104 Image processing unit
105 control unit
106 Printer Engine
107 Central Processing Unit (CPU)
108 Lead-on memory (ROM)
109 Random access memory (RAM)
141 receive buffer
142 Color conversion mode setting section
143 Color conversion parameter holding unit
144 color conversion unit
145 color conversion table
146 Color shift amount processing unit
147 Density correction processing unit
148 Density correction table
149 Matrix setting section
150 Dither parameter storage
151 Dither processing unit
152 dither table
153 Object generator
154 Object buffer
155 rendering unit
156 band buffer
157 PWM processing unit
158 PWM pattern table
401 Color shift pattern measurement unit
402 Color shift amount calculation unit
403 line memory reading unit
404 line memory
405 color shift pattern generator

Claims (12)

An image processing apparatus for a color image forming apparatus that forms a color image by performing pulse width modulation processing for each color component data and performing line scanning,
Color shift processing means for inputting color shift information of the color component data in the main scanning direction;
Setting means for setting a pulse width growth pattern of the pulse width modulation process according to the color misregistration information. The color misregistration processing means,
Patch pattern generating means for generating an image of a predetermined patch pattern,
2. A color shift information generating means for measuring a color shift amount in a main scanning direction from an image formed by the patch pattern generated by the patch pattern generating means and generating the color shift information. 2. The image processing device according to 1. Input means for inputting color component data constituting a color image,
Pseudo gradation processing means for converting the color component data into pseudo gradation data;
3. The pulse width modulation unit according to claim 1, further comprising a pulse width modulation unit configured to pulse width modulate the color component data processed by the pseudo gradation processing unit with a pulse width growth pattern set by the setting unit. Image processing device. The image processing apparatus according to claim 3, wherein the pulse width modulation unit includes a plurality of pattern tables having different pulse width growth patterns, and selects the plurality of pattern tables according to the color misregistration information. The image processing apparatus according to claim 4, wherein the plurality of pattern tables have different pulse width growth patterns within one pixel. An image processing method for a color image forming apparatus that forms a color image by performing a pulse width modulation process for each color component data and scanning a line,
A color shift processing step of inputting color shift information of the color component data in the main scanning direction;
Setting a pulse width growth pattern of the pulse width modulation process in accordance with the color misregistration information. The color shift processing step,
A patch pattern generating step for generating an image of a predetermined patch pattern,
A color shift information generating step of measuring a color shift amount in a main scanning direction from an image formed by the patch pattern generated in the patch pattern generating step and generating the color shift information. 7. The image processing method according to 6. A pseudo gradation processing step of converting color component data constituting the color image into pseudo gradation data;
8. A pulse width modulation step of pulse width modulating the color component data processed in the pseudo gradation processing step with a pulse width growth pattern set in the setting step. Image processing method. 9. The image processing method according to claim 8, wherein in the pulse width modulation step, a desired table is selected from a plurality of pattern tables provided in advance with different pulse width growth patterns according to the color misregistration information. 10. The image processing method according to claim 9, wherein the plurality of pattern tables have different pulse width growth patterns within one pixel. A program for causing a computer to control a color image forming apparatus that forms a color image by performing pulse width modulation processing for each color component data and performing line scanning,
A color shift processing procedure for inputting color shift information of the color component data in the main scanning direction;
A setting procedure for setting a pulse width growth pattern of the pulse width modulation processing according to the color misregistration information. A computer-readable recording medium storing the program according to claim 11.

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