JP2007316121A - Color image forming apparatus, image forming method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent color smearing due to inclination or curving, etc., in a scanning beam exposing an image carrier and to obtain low cost. <P>SOLUTION: A color image forming apparatus is provided with; a gradation correction control means controlling a buffer means storing data based on the data generated by an address control means and also controlling the gradation correction means carrying out gradation correction based on exposure shifted amount information stored to an exposure shifted amount storing means and an output means outputting pixel data obtained by the gradation correction means as exposure control signal for an exposure part of a corresponding image forming part. The problem is solved by having an optical beam obtained based on the outputted image data by the gradation correction means respectively exposed on each photoreceptor by each exposure means for each image station. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus, an image forming method, and a program.

  2. Description of the Related Art Conventionally, as a color image forming apparatus using an electrophotographic system, one that performs development with each color component using a plurality of developing units for one photoconductor is known. This device repeats the “exposure-development-transfer” process by the number of color components, and in each case, forms a color image on a single transfer paper and fixes it to obtain a full-color image. It is.

  According to this method, in order to obtain one printed image, it is necessary to repeat the image forming process 3 to 4 times (when black is used), and it takes time to complete the image formation. was there. As a method for compensating for this drawback, a technique is known in which a plurality of photoconductors are used, and a visible image obtained for each color is sequentially superposed on a transfer paper to obtain a full color print by one pass.

  According to this method, the throughput can be greatly shortened. However, on the other hand, there is a problem of color misregistration due to misregistration on the transfer paper of each color due to misregistration of each photoconductor, deviation of diameter, misregistration of optical system, etc., and a high-quality full color image is obtained. There is a problem that it becomes difficult.

  As a method for preventing this color misregistration, for example, a test toner image is formed on a transfer belt or a conveyance belt forming a part of transfer means, and this is detected, and each optical system is detected based on this result. There is known a technique for correcting the optical path of each color or correcting the image writing position of each color (see, for example, Patent Document 1).

  Further, the output coordinate position of the image data for each color is automatically converted into an output coordinate position in which the registration deviation is corrected, and the light beam position modulated by the correcting means based on the converted image data of each color is converted into the color signal. A technique for correcting with an amount smaller than the minimum dot unit is also known (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 64-40956 JP-A-8-85237

  However, the following problem remains in Patent Document 1 described above. First, in order to correct the optical path of the optical system, it is necessary to mechanically operate a correction optical system including a light source and an f-θ lens, a mirror in the optical path, etc., and adjust the position of the test toner image. . That is, a highly accurate movable member is required, and the cost must be increased. Furthermore, since it takes time to complete the correction, it is impossible to perform correction frequently. Further, the optical path length deviation may change with time due to the temperature rise of the machine. In such a case, it is difficult to prevent the color deviation by correcting the optical path of the optical system. Second, by correcting the image writing position, it is possible to correct the displacement of the left end and the upper left portion, but it is not possible to correct the tilt of the optical system or the magnification shift due to the deviation of the optical path length.

  In Patent Document 2, a line buffer for one line is always required when correcting the position of the light beam by an amount smaller than the minimum dot unit of the color signal, which is a major factor in increasing the cost. Yes.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to prevent color misregistration due to the inclination and curvature of a scanning line for exposing an image carrier and to realize cost reduction.

  In order to solve the above problems, the present invention provides an image carrier, an exposure unit that scans and exposes the image carrier, and a developing unit that visualizes the electrostatic latent image generated by the exposure with a recording material. And an image data storage unit for recording image data to be formed in each image forming unit, the image forming unit having the image forming unit arranged in parallel along the conveyance direction of the recording medium, An exposure shift amount storage unit that stores shift amount information indicating a shift amount with respect to the exposure scanning direction on the image carrier of the image forming unit, and each region based on the exposure shift amount information stored in the exposure shift amount storage unit A color misregistration amount calculating means for calculating the inclination information of the exposure misalignment in the image, and address coordinates of the image data recording means based on the information obtained from the color misregistration amount calculating means, and reading the image data according to the address information. And address control means for generating data with gradation correction control data added to the read pixel data based on the exposure deviation amount information stored in the exposure deviation amount storage means, and the address Control of buffer means for storing data based on data generated by the control means, and control of gradation correction means for performing gradation correction based on exposure deviation amount information stored in the exposure deviation amount storage means Gradation correction control means for performing the above and output means for outputting pixel data obtained by the gradation correction means as an exposure control signal for the exposure unit of the corresponding image forming unit, the gradation correction unit The exposure means of each image station exposes the light beam obtained on the basis of the image data output by the above-mentioned photoconductors.

  By adopting such a configuration, it is possible to prevent color misregistration due to the inclination, curvature, etc. of the scanning line for exposing the image carrier, and to realize cost reduction.

  In order to solve the above problem, the present invention may be an image forming method and a program.

  According to the present invention, it is possible to prevent color misregistration due to the inclination, curvature, etc. of the scanning line for exposing the image carrier and to realize cost reduction.

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

  FIG. 1 is a structural cross-sectional view of an image forming apparatus according to the present embodiment. In this image forming apparatus, a transfer material cassette 53 is mounted on the lower right side of the figure. The recording medium (recording paper, transmission sheet, etc.) set in the transfer material cassette 53 is taken out one by one by the paper feed roller 54 and fed to the image forming unit by a pair of transport rollers 55-a and 55-b. . In the image forming unit, a transfer conveyance belt 10 that conveys the recording medium is stretched flat in the recording medium conveyance direction by a plurality of rotating rollers, and the recording medium is electrostatically attracted to the conveyance belt 10 in the most upstream part. The Further, four photosensitive drums 14-C, Y, M, and K serving as drum-shaped image bearing members are arranged in a straight line so as to face the belt conveyance surface to constitute an image forming unit (here. C represents cyan, Y represents yellow, M represents magenta, and K represents black.) Since the image forming unit for each color component is different only in the color of the toner to be mounted and there is no structural difference, the color component C will be described.

  The C-color image forming unit stores a charger 50-C for uniformly charging the surface of the photosensitive drum 14-C, C-color toner, and an electrostatic latent image generated on the photosensitive drum 14-C. It has a developing device 52-C for developing (developing) a visible image and an exposure unit 51-C. A predetermined gap is provided between the developing unit 52-C and the charger 50-C. On the photosensitive drum 14-C whose surface is uniformly charged by the charger 50-C, the laser beam from the exposure unit 51-C made of a laser scanner is scanned and exposed in the direction perpendicular to the drawing through the gap. . Thus, a charged state different from the non-exposed portion, that is, an electrostatic latent image is generated in the scanned and exposed portion. The developing device 52-C transfers the toner to the electrostatic latent image to make a visible image (toner image; development).

  A transfer portion 57 -C is arranged across the conveyance surface of the transfer conveyance belt 10. The toner image formed (developed) on the peripheral surface of the photosensitive drum 14-C is charged and adsorbed onto the conveyed recording medium by the transfer electric field formed by the transfer unit 57 corresponding to the toner image. Transferred onto the medium surface.

  By performing the above-described processing for the other color components Y, M, and K in the same manner, the C, M, Y, and K color toners are successively transferred to the recording medium. Thereafter, each color toner on the recording medium is melted and fixed by the fixing device 58, and is discharged out of the apparatus by a pair of paper discharge rollers 59-a and 59-b.

  The above is an example of transferring a toner image of each color component onto a recording medium. However, when the toner images of the respective color components are transferred onto the transfer / conveyance belt, the toner image generated on the transfer / conveyance belt may be transferred again to the recording medium (secondary transfer). The transfer belt in this case is called an intermediate transfer belt.

  FIG. 2 is an image diagram for explaining the shift of the main scanning line scanned on the photosensitive drum 14-C (which may be M, Y, or K) which is an image carrier. The horizontal direction in the figure indicates the scanning direction of the laser beam, and the vertical direction indicates the rotation direction of the photosensitive drum (also the conveyance direction of the recording medium). 201 in the figure represents an ideal main scanning line. Reference numeral 202 denotes an actual main scanning line in which the positional accuracy and the diameter of the photosensitive drum 14 are shifted, the inclination of the right upward due to the positional accuracy of the optical system in each color exposure unit 51-C, and the curvature are generated. An example is shown. When such an inclination or curvature of the main scanning line exists in any color image forming unit, color misregistration occurs when a plurality of color toner images are collectively transferred to the transfer medium.

  In the present embodiment, in the main scanning direction (X direction), an ideal main scanning line at a plurality of points (point B, point C, point D) with the point A serving as the scanning start position of the print area as a reference point. The amount of deviation in the sub-scanning direction between 201 and the actual main scanning line 202 is measured. Then, each point where the amount of deviation is measured is divided into a plurality of regions (region Pa-Pb is region 1, region Pb-Pc is region 2, and region Pc-Pd is region 3). The slope of the main scanning line in each region is approximated by straight lines (Lab, Lbc, Lcd) connecting the two.

  Accordingly, when the difference in the amount of deviation between points (m1 for area 1, m2-m1 for area 2, m3-m2 for area 3) is a positive value, the main scanning line of the corresponding area has an upward slope. In the case of a negative value, it indicates that it has a downward slope. In the present embodiment, the number of regions is three, but this is for convenience and is not limited to this number.

  FIG. 3 is a block diagram for explaining the operation of the color misregistration correction process for correcting the color misregistration caused by the inclination and curvature of the scanning line performed in this embodiment. In the figure, reference numeral 301 denotes a printer engine, which actually performs print processing based on image bitmap information generated by the controller 302. The controller 302 is accommodated in the substrate, and when it is accommodated in the apparatus, electrical connection with the printer engine 301 is performed.

  303C, M, Y, and K are exposure unit profiles for each color, and write and hold the deviation amount information for each image forming unit for each color in the apparatus manufacturing stage. As an example, it can be realized by a writable nonvolatile memory such as an EEPROM. In the drawing, an exposure unit profile is provided for each color component. However, since the amount of information to be stored is sufficiently small, the exposure unit profiles for all color components may be stored in one memory element. The exposure unit profiles 303C, M, Y, and K in the present embodiment are the deviations in the sub-scanning direction between the actual main scanning line 201 measured at a plurality of points and the ideal main scanning line as described in FIG. Color misregistration amount information is stored as information indicating the inclination and curvature of the main scanning line.

  FIG. 4 shows an example of information stored in the exposure unit profile 303C (M, Y, and K are the same, but the stored information varies depending on individual differences), and L1 to L3 and m1 to m3 has the same meaning as in FIG. In this embodiment, the deviation amount between the ideal main scanning line and the actual main scanning line is stored in the exposure unit profile. However, the actual main scanning line inclination and curvature characteristics are stored. If is identifiable information, it is not limited to this.

  Further, as described above, the information stored in the exposure unit profiles 303C, 303M, 303Y, 303K is measured in advance in the manufacturing process and stored in advance as information unique to the apparatus. However, a detection mechanism for detecting the amount of deviation is prepared in the apparatus itself, a predetermined pattern for measuring the deviation is formed for each color image carrier, and the amount of deviation detected by the detection mechanism is stored. Such a configuration may be used. The controller 302 performs the printing process by correcting the image data for each color component so as to cancel out the shift amounts of the main scanning lines stored in the exposure unit profiles 303C, M, Y, and K. The following is a description of the controller 302 in the embodiment.

  Returning to the description of FIG. 3 again, the image generation unit 304 generates raster image data that can be printed from print data (PDL data, image data, etc.) received from an external device (for example, a computer device) not shown. Then, RGB data (256 gradations of 8 bits each) is output for each dot. Since this process is a well-known process, detailed description is omitted. The color conversion unit 305 converts the RGB data into CMYK space data (8 bits each) that can be processed by the printer engine 302 (implemented by LOG conversion and UCR processing), and the subsequent bitmap memories 306C, M, Accumulate in Y and K. The bitmap memory 306C (same for M, Y, and K) temporarily stores raster image data to be printed, and includes a page memory that stores image data for one page. However, any of band memories that store data for a plurality of lines may be used. In order to simplify the description, it is assumed here that the data has a capacity for storing C, M, Y, K bitmap data for one page.

The color misregistration correction amount calculation units 307C, M, Y, and K are sub-data corresponding to the coordinate information in the main scanning direction based on the main scanning line misalignment information accumulated in the exposure unit profiles 303C, M, Y, and K. A color misregistration correction amount in the scanning direction is calculated. Then, the result is output to the color misregistration correction units 308C, M, Y, and K, respectively, and set. When the coordinate data in the main scanning direction is x (dots) and the color shift amount in the sub-scanning direction is y (dots), the calculation formulas for each region based on FIG. 2 are as follows. Note that the recording resolution in the embodiment is 600 dpi.
Region 1: y = x * (m1 / L1)
Region 2: y = m1 * 23.622 + (x−L1 * 23.622) * ((m2−m1) / (L2−L1))
Region 3: y = m2 * 23.622 + (x−L2 * 23.622) * ((m3−m2) / (L3−L2)) (1)

  Here, L1, L2, and L3 are distances (unit: mm) in the main scanning direction from the print start position to the right ends of the regions 1, 2, and 3. m 1, m 2, and m 3 are deviation amounts between the ideal main scanning line 201 and the actual main scanning line 202 at the left end of the regions 1, 2, and 3. The color misregistration correction units 308C, M, Y, and K are dots by color misregistration amount calculation units 307C, M, Y, and K, respectively, in order to correct the color misregistration due to the inclination and distortion of the main scanning line in the above equation (1). Based on the color misregistration correction amount calculated every time, the output address control and timing adjustment of the bitmap data stored in the bitmap memory 306 and the exposure amount adjustment for each pixel are performed. This prevents color misregistration (registration misalignment) when transferred to a transfer medium. Then, the pixel data corrected by the color misregistration correction units 308C, M, Y, and K is output to the PWM processing units 309C, M, Y, and K, where a known pulse width modulation signal is generated, and each exposure unit Scan exposure is performed at 51-C, M, Y, and K. Although the color misregistration correction units 308C, M, Y, and K have different correction amounts but have the same configuration, only the C component color misregistration correction unit 308C will be described here.

  FIG. 5 is a block configuration diagram of the color misregistration correction unit 308C in the embodiment. As shown in the figure, the color misregistration correction unit 308C according to the embodiment includes an address control unit 501, a tone correction control unit 505, a buffer memory 506, a tone, and a coordinate counter 502, an address generation unit 503, and a data generation unit 504. The correction unit 507 is configured. The color misregistration correction unit 308C turns ON / OFF the correction processing for the integer part of the correction amount Δy obtained from the color misregistration amount calculation unit 307C and the correction processing for the fractional part of Δy, that is, dots before and after the sub-scanning direction in less than a pixel unit. The gradation is corrected by adjusting the OFF ratio.

  The coordinate counter 502 generates coordinates in the main scanning direction and the sub-scanning direction for performing color misregistration correction processing based on the equation (1) shown above.

The address generation unit 503 uses the coordinate position data in the main scanning direction from the coordinate counter 502, the coordinate position data in the sub-scanning direction, the correction position, the correction range, and the correction amount information from the color misregistration amount calculation unit 307C. Read access to the memory 406 is performed. The address to be accessed has a correction processing function for the integer part of the correction amount Δy obtained from the color misregistration amount calculation unit 307C. By changing the pixel coordinates to be read, correction processing is performed on the integer part of the correction amount Δy obtained from the color misregistration amount calculation unit 307C. Further, the correction range is determined from the correction amount Δy obtained from the color misregistration amount calculation unit 307C and the correction position, and the pixel coordinates to be read are changed accordingly. As a result, the read data (here, C component data) is input to the data generation unit 504. An image diagram of pixel coordinates read out from the bitmap memory 406 by the address generation unit 503 is shown in FIG.

FIG. 6A is an image diagram of an image developed on the bitmap memory 306. Reference numeral 601 denotes an example of the inclination of the main scanning line, and is an image diagram of information obtained from the color misregistration amount calculation unit 307C. In addition, the shaded portions of the region 2, the region 4, and the region 6 indicate regions where it is necessary to perform correction processing after the decimal point of the correction amount Δy. In the situation shown in FIG. 6A, by outputting the image shown in FIG. 6B to the printer engine (301 in FIG. 3), the inclination as shown in 601 is canceled and a horizontal image is formed. The Rukoto. In order to output an image as shown in FIG. 6B to the printer engine (301 in FIG. 3), the order of data areas read by the address generation unit 503 in this embodiment is shown in FIG. 6C. In order to form the data for the first line in FIG. 6B, the pixel data in the areas A1 to A10 in FIG. 6C are read in order, and the data for the second line in FIG. In order to form the pixel data, it is necessary to sequentially read out the pixel data in the region from B1 to B10 in FIG.

  In this way, for the data read from the bitmap memory 306 by the address generation unit 503, the data generation unit 504 adds additional data based on the correction position and correction range information from the color misregistration amount calculation unit 307C. The data is output to the embedding and gradation correction control unit 505.

  The tone correction control unit 505 controls the buffer memory 506 and the tone correction unit 507 based on the additional data in the input data stream. An example of the processing will be described using an example of a data stream input to the gradation correction control unit 505 shown in FIG.

  The gradation correction control unit 505 uses the gradation correction ON / OFF information 701A and 701B and the range information 702A and 702B embedded in the input data stream from the coordinate position in the main scanning direction of interest at the present time. It is determined whether or not gradation correction processing is performed for pixel data within a certain range.

  When the gradation correction ON / OFF information is ON (701A), it is determined that the buffer memory storage data continues for the range information 702A after the range information 702A, and the data is stored in the buffer memory 506. After storing the data for the range information 702A, the non-buffer memory storage data continues for the range information 702A. Therefore, the non-buffer memory data is input to the gradation correction unit 507, and at the same time, the buffer memory storage data is read from the buffer memory. .

  The read buffer memory storage data is output to the gradation correction unit 507. When the gradation correction ON / OFF information is OFF (701B), it is determined that the non-buffer memory storage data 704B continues for the range information 702B after the range information 702B. Then, simultaneously with the input of the non-buffer memory storage data 704B to the gradation correction unit 507, a control signal indicating that gradation correction unprocessed data is output is output to the gradation correction unit 507.

  The gradation correction unit 507 uses the pixel value output from the gradation correction control unit 505 and the pixel value output from the buffer memory 506, pixel data that has been corrected for color misregistration less than a pixel unit, Pixel data that has not undergone color misregistration correction is selected by a control signal output from the gradation correction control unit 505. Here, an image diagram for explaining the operation content of the gradation correction processing is shown in FIG.

FIG. 8 is an image diagram for explaining an operation content for correcting a color misregistration correction less than a pixel unit performed by the gradation correcting unit 507 in the embodiment, that is, correcting a misregistration amount of the color misregistration correction inclination Δy after the decimal point.

Correction of the shift amount after the decimal point is performed by adjusting the exposure ratio of dots before and after in the sub-scanning direction. FIG. 8A is an image of a main scanning line having a slope rising to the right. FIG. 8B is a bitmap image of a horizontal straight line before gradation correction, and FIG. 8C is a correction image for canceling color misregistration due to the inclination of the main scanning line in FIG. It is. In order to realize the generation of the corrected image in FIG. 8C, the exposure amount adjustment of dots before and after the sub-scanning direction is performed. FIG. 8D is a table showing the relationship between the correction slope Δy of color misregistration and the correction coefficient for performing gradation correction. k is an integer part of the color misregistration correction amount Δy (the fractional part is rounded down), and represents the correction amount in the sub-scanning direction in units of pixels. β and α are correction coefficients for correcting in the sub-scanning direction less than a pixel unit. α represents the preceding dot (the distribution rate for the data output from the buffer memory 506 in FIG. 5), and β represents the distribution rate of the target pixel output from the gradation correction control unit 505.

  FIG. 8D is a bitmap image that has been subjected to tone correction for adjusting the exposure ratio of dots before and after the sub-scanning direction in accordance with the correction coefficient shown in FIG. FIG. 8E shows an exposure image of the bitmap-corrected bitmap image on the image carrier, in which the inclination of the main scanning line is canceled and a horizontal straight line is formed.

  Although the color misregistration correction unit 308C in the embodiment has been described above, the same applies to the color misregistration correction units 308M, Y, and K of the other color components M, Y, and K, so that the maximum color misregistration between recorded colors can be achieved. It can be set to less than one pixel.

  As described above, according to the present embodiment, in a tandem type color image forming apparatus having a plurality of image forming units, distortion such as inclination and curvature of a scanning line held in a memory or the like that scans the image carrier itself. The color misregistration correction amount calculation unit calculates the color misregistration correction amount from the color misregistration amount due to. Then, based on the color misregistration correction amount, the color misregistration correction unit performs color misregistration correction in units of pixels and color misregistration correction in units of pixels with a gradation expression by a plurality of pixels, and reconstructs an image bitmap. As a result, it is possible to prevent color misregistration due to the inclination or curvature of the scanning line for exposing the image carrier. At that time, the color misregistration correction unit can realize cost reduction by performing access coordinate control and data control of the bitmap memory.

  That is, it is possible to prevent color misregistration due to the inclination, curvature, etc. of the scanning line for exposing the image carrier and to realize cost reduction.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims.・ Change is possible.

1 is a cross-sectional structure diagram of an image forming apparatus. It is a figure explaining the shift | offset | difference of the main scanning line scanned to a photosensitive drum. It is a block block diagram with a controller and an engine. It is a figure which shows the example of the information memorize | stored in the exposure unit profile. It is a block block diagram of a color misregistration correction unit. It is a figure which shows the operation | movement performed by the address generation part in a color misregistration correction part. It is a figure which shows the example of a data stream input into the gradation correction control part in a color misregistration correction part. It is a figure which shows the operation | movement which a gradation correction | amendment part correct | amends color shift less than a pixel unit.

Explanation of symbols

301 Printer Engine 302 Controller 303 Exposure Unit Profile 304 Image Generation Unit 305 Color Conversion Hand Unit 306 Bitmap Memory 307 Color Shift Amount Calculation Unit 308 Color Shift Correction Unit

Claims (8)

An image forming unit having an image carrier, an exposure unit that scans and exposes the image carrier, and a developing unit that visualizes the electrostatic latent image generated by the exposure with a recording material. An image forming apparatus arranged side by side,
Image data storage means for recording image data to be formed in each image forming unit;
An exposure deviation amount storage means for storing deviation amount information indicating a deviation amount with respect to an exposure scanning direction on the image carrier of the image forming unit;
Color misregistration amount calculating means for calculating inclination information of exposure deviation in each region based on exposure deviation amount information stored in the exposure deviation amount storage means;
Based on the information obtained from the color misregistration amount calculating means, the address coordinates of the image data recording means are controlled, the image data is read according to the address information, and the exposure deviation amount storage is stored for the read pixel data. Address control means for generating data to which gradation correction control data is added based on exposure deviation amount information stored in the means;
Control of buffer means for storing data based on data generated by the address control means, and gradation correction means for performing gradation correction based on exposure deviation amount information stored in the exposure deviation amount storage means Gradation correction control means for controlling
Output means for outputting the pixel data obtained by the gradation correction means as an exposure control signal of an exposure section of a corresponding image forming section;
Have
A color image forming apparatus, wherein each exposure unit of each image station exposes a light beam obtained on the basis of the image data output by the gradation correction unit onto each photoconductor.   The exposure deviation amount storage means includes position information regarding a plurality of positions in the main scanning direction, which is the ideal scanning exposure direction of the image carrier, and distance information regarding the distance between the ideal scanning exposure and the actual exposure at each position. The color image forming apparatus according to claim 1, wherein:   The color misregistration amount calculation means calculates exposure misalignment inclination information in each area indicated by each position information based on the position information and distance information stored in the exposure deviation amount storage means. The color image forming apparatus according to claim 2.   The address control unit reads out image data from the image data storage unit based on the inclination information of the exposure shift in each region indicated by the position information obtained by the color misregistration amount calculation unit. 4. The color image forming apparatus according to claim 3, further comprising control data for controlling the gradation correction unit.   The gradation correction control means performs control of writing and reading to the buffer means and control of the gradation correction means based on data obtained by the address control means. 2. A color image forming apparatus according to 1.   The gradation correction means performs gradation correction using the data read from the buffer means and the pixel data input by the gradation correction control means, and the gradation corrected pixel data and the gradation correction 6. The color image forming apparatus according to claim 1, wherein pixel data not to be selected is selected and output as an exposure control signal of a corresponding image forming unit. An image forming unit having an image carrier, an exposure unit that scans and exposes the image carrier, and a developing unit that visualizes the electrostatic latent image generated by the exposure with a recording material. An image forming method in an image forming apparatus arranged along the line,
An image data storage step of recording image data to be formed in each image forming unit in an image data storage means;
An exposure shift amount storing step of storing shift amount information indicating a shift amount with respect to an exposure scanning direction on the image carrier of the image forming unit in an exposure shift amount storage unit;
A color misregistration amount calculating step of calculating exposure misalignment inclination information in each region based on the exposure misalignment amount information stored in the exposure misalignment amount storage means;
Based on the information obtained from the color misregistration amount calculating step, the address coordinates of the image data recording means are controlled, the image data is read according to the address information, and the exposure misregistration amount memory is stored for the read pixel data. An address control step for generating data to which gradation correction control data is added based on exposure deviation amount information stored in the means;
Control of buffer means for storing data based on data generated by the address control step, and gradation correction means for performing gradation correction based on exposure deviation amount information stored in the exposure deviation amount storage means A gradation correction control process for controlling
An output step of outputting pixel data obtained by the gradation correction means as an exposure control signal of an exposure unit of a corresponding image forming unit;
Have
A color image forming method, wherein each exposure means of each image station exposes a light beam obtained based on the image data output by the gradation correction means on each photoconductor.   A program for causing a computer of an image forming apparatus to execute the color image forming method according to claim 7.

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