JP2009027683A - Image correcting device, image forming apparatus, and image correcting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce deterioration in image quality when outputting an image at an image-shifting position during skew-correction. <P>SOLUTION: When starting positional deviation correction, positional deviation correction patterns generated by a positional deviation correction pattern generating unit are formed on a transfer belt (SA-1). Detection sensors detect the correction patterns (SA-2), and amounts of magnification correction in the main-scanning direction with respect to a reference color and amounts of mis-registration in the main- and the sub-scanning direction are calculated (SA-3). The amount of skew with respect to the reference color is then calculated (SA-4), and a dividing position in the main-scanning direction for performing skew-correction and a correction direction are determined (SA-5). Regarding the dividing position in the main-scanning direction for performing the skew-correction, possible dividing-positions are also determined beforehand, and a calculated dividing position and each of the possible dividing positions are compared with one another. Then, a possible dividing position closest to the calculated dividing position is set as the dividing position in the main-scanning direction for performing skew-correction (SA-6). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image correction apparatus, an image forming apparatus, and an image correction method for correcting color misregistration when forming a color image using a plurality of photoconductors.

  When performing skew correction or skew correction by image processing in the alignment processing of a color image forming apparatus, correction is performed by shifting an image divided in the main scanning direction in the sub-scanning direction, but pseudo halftone processing such as dither processing When the generated image is shifted, the dither pattern may be lost at the image shift position, and a noise image may be generated.

  That is, in the color image forming apparatus, an alignment technique between each color is an important issue due to its configuration. For this reason, in the color image forming apparatus, a predetermined toner pattern is formed with toner of each color on the transfer belt, and the amount of deviation between the colors is detected by detecting this toner pattern using an optical sensor. In many cases, color misregistration is reduced by calculating according to factors such as main / sub registration deviation, magnification deviation, skew, and bending, and performing feedback correction so that they match each other. Further, this correction process is performed when the power is turned on, when the environment such as temperature changes, or when a certain number of sheets are printed, so that the color misregistration amount is always within a certain range.

  Among the shift amounts, the main and sub resists can be electrically corrected by adjusting the writing timing and the main scanning magnification by adjusting the pixel clock. On the other hand, the skew of the scanning beam includes a method of correcting mechanically and a method of correcting the output image by transforming the output image in the reverse direction by image processing and outputting the image.

  In the mechanical correction method, correction is realized by providing an adjustment mechanism that displaces the mirror inside the writing unit. However, in order to perform this adjustment automatically, an actuator such as a motor is required, which increases costs. Will be invited. Also, the writing unit cannot be made smaller. On the other hand, a correction method using image processing is to correct a skew between colors by accumulating a part of an image in a line memory and reading the image while switching a reading position. In this case, it is only necessary to add a line memory to the image processing unit in accordance with the correction range, so that it can be realized at a relatively low cost compared to mechanical correction and can be corrected automatically, thereby reducing the skew. It is already known as effective. Further, it is already known that the method is effective as a method of reducing not only skew but also bending caused by the characteristics of the lens inside the writing unit.

As such a correction method, for example, the invention described in Patent Document 1 is known. In the present invention, when correcting image images of different colors, the divided positions are moved so that the divided positions of the corrected image images do not approach each other. Thereby, when correcting the parallelism deviation in the registration, the trace of the correction is visually recognized and the image quality is prevented from being deteriorated.
JP 2001-353906 A

  However, the method of correcting by image processing is to store a part of the image in a plurality of line memories, read out while switching the readout line, and shift the image divided in the main scanning direction to the sub-scanning direction to shift between the colors. Or it reduces the bending. For this reason, a change occurs in the dither pattern at the shift position of the image. When the dither pattern changes, the adjacent relationship of the pixels in the main scanning direction changes (for example, changes from a white pixel to a black pixel), and the toner adhesion area at the time of output changes. In an image expressed by a pseudo gradation process such as a dither method, this toner adhesion area fluctuation frequently and periodically occurs in the sub-scanning direction, and a streak noise image appears on the recorded image (on the printing paper). To occur.

  That is, when skew correction (including bending correction) is performed by image processing, if the dither pattern changes at the image shift position, the toner adhesion area at the time of output fluctuates, and the image processing such as dither processing causes the sub-scanning direction. There is a problem in that a noise image is generated due to frequent occurrence of a toner adhesion area fluctuation portion, and the image quality is greatly deteriorated.

  Therefore, a problem to be solved by the present invention is to reduce image quality degradation at the time of image output at the skew image shift position.

  In order to achieve the above-described object, the present invention is an image correction apparatus based on a main scanning size that is a size in a main scanning direction of a dither matrix used for dither processing and a distance between image patterns of the dither matrix. A first calculation unit that calculates a position where the image pattern does not exist and determines the calculated position as a plurality of image shift candidate positions at the time of skew correction processing on the input image; and image division when performing skew correction processing A second calculation unit that calculates a position based on a deviation amount of the correction target color with respect to a reference color, a comparison unit that compares the image shift candidate position and the image division position, and a plurality of image shift candidate positions. A determination unit that determines a position closest to the image division position as an image shift position that is a division position in the main scanning direction during skew correction processing; Based on the image shift position, characterized by comprising a correction unit for performing skew correction processing for the input image.

  The present invention also provides an image forming apparatus and an image correction method having the above image correction apparatus.

  According to the present invention, image data is divided at a position where there is no image pattern of a dither matrix formed on the image forming medium in the main scanning direction, and is shifted in the sub-scanning direction at the divided position. ) Image collapse is minimized at the image shift position at the time of correction, and as a result, image quality degradation at the time of image output can be reduced.

  Exemplary embodiments of an image correction apparatus, an image forming apparatus, and an image correction method according to the present invention are explained in detail below with reference to the accompanying drawings.

  FIG. 1 is a diagram showing a schematic configuration of the image forming apparatus according to the first embodiment. The image forming apparatus shown in FIG. 1 is an example of a so-called direct transfer tandem image forming apparatus. In FIG. 1, the image forming apparatus basically includes an image forming process unit 1, an optical writing unit (exposure unit) 9, and a paper feeding unit (paper feeding tray) 6. The image forming process unit 1 is configured such that each station that forms an image of a different color (yellow: Y, magenta: M, cyan: C, black: K) is applied to a transfer belt 3 that conveys a transfer sheet 2 as a transfer medium. It is arranged in a line along.

  The transfer belt 3 is stretched between a drive roller 4 that is driven to rotate and a driven roller 5 that is driven to rotate, and is driven to rotate in the direction of the arrow in FIG. Under the transfer belt 3, a paper feed tray 6 containing the transfer paper 2 is provided, and functions as a paper feed unit. The transfer sheet 2 at the uppermost position among the transfer sheets 2 stored in the sheet feed tray 6 is fed toward the transfer belt 3 at the time of image formation.

  The transfer sheet 2 conveyed to the transfer unit is conveyed to the first image forming station 1Y (yellow), where yellow image formation is performed. The first image forming station 1Y includes a photoreceptor drum 7Y, a charger 8Y, a developer 10Y, and a photoreceptor cleaner 11Y arranged around the photoreceptor drum 7Y. The charger 8Y and the developer 10Y In the meantime, an exposure unit to which the laser beam LY is irradiated from the exposure unit 9 is provided.

  The surface of the photosensitive drum 7Y is uniformly charged by the charger 8Y, and then exposed by the exposure device 9 with the laser light LY corresponding to the yellow image, thereby forming an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 10Y, and a toner image is formed on the photosensitive drum 7Y. This toner image is transferred to the transfer paper 2 by the transfer device 12Y at a position (transfer position) where the photosensitive drum 7Y and the transfer paper 2 on the transfer belt 3 are in contact with each other. ) Is formed. In the photoreceptor drum 7Y after the transfer, unnecessary toner remaining on the drum surface is cleaned by the photoreceptor cleaner 11Y to prepare for the next image formation.

  As described above, the transfer paper 2 on which the single color (yellow) is transferred by the first image forming station 1Y (yellow) is conveyed by the transfer belt 3 to the second image forming station 1M (magenta). Similarly, the toner image (magenta) formed on the photosensitive drum 7M is transferred onto the transfer paper 2 in a similar manner. The transfer paper 2 is further conveyed in order to the third image forming station 1C (cyan) and the fourth image forming station 1K (black). Similarly, the formed toner images are sequentially superimposed on the transfer paper 2. As a result, a color image is formed on the transfer paper 2. The second, third, and fourth image forming stations 1M, 1C, and 1K (magenta, cyan, and black) have the same configuration as that of the first image forming station 1Y (yellow). The description is omitted after clarifying that the image forming station is for each color.

  The transfer paper 2 on which the color images are superimposed by the first to fourth image forming stations 1Y, 1M, 1C, and 1K to form a full-color image is peeled off from the transfer belt 3 and fixed by the fixing device 13. Are discharged.

  FIG. 2 is a perspective view of the transfer belt 3 and the photosensitive drums 7Y, 7M, 7C, and 7K showing a state in which a correction pattern 14 for correcting misregistration is formed on the transfer belt 3. In the tandem type color image forming apparatus shown in FIG. 1, an alignment technique between colors becomes an important issue because of its configuration. Therefore, in the color image forming apparatus according to the present embodiment, the positional deviation correction of each color is performed before the actual color image forming operation is performed on the transfer paper 2.

  For this purpose, first, a correction pattern 14 for correcting misregistration of each color is formed on the transfer belt 3, and this is detected by a plurality of detection sensors. In the present embodiment, two detection sensors 15 and 16 are arranged at both ends of the transfer belt 3 in the main scanning direction, and the correction pattern 14 is arranged on the transfer belt 3 in correspondence with the arrangement positions of the detection sensors 15 and 16. Form. The correction pattern 14 is detected when the transfer belt 3 rotates and moves and sequentially passes through the detection sensors 15 and 16. When the correction pattern 14 is detected, various deviation amounts and correction amounts are calculated from the detection results, and each deviation component is corrected.

  FIG. 3 is a block diagram mainly showing an engine control unit for executing write control and positional deviation correction in the present embodiment, and FIG. 4 is a block diagram showing details of the write control unit in FIG.

  In FIG. 3, the engine control unit 114 includes a CPU 110, a RAM 111, an image processing unit 112, a pattern detection unit 113, and a write control unit 101. Pattern detection sensors 15 and 16 are connected to the pattern detection unit 113, and detection signals are input. The detection output of the pattern detection unit 113 is input to the CPU 110. The CPU 110 executes a program stored in a ROM (not shown) while using the RAM 111 as a work area, and controls the write control 101 and the entire engine control unit.

  The write control unit 101 is provided with write control units 102, 103, 104, and 105 as shown in FIG. 4 for each color of KMCY. Signals necessary for writing an image from the image processing unit 112 are input to the writing control units 102, 103, 104, and 105 for each color. The image processing unit 112 transmits and receives signals to and from the printer controller 115 and the scanner 116. A printer image from a PC (not shown) is processed by the printer controller 115, and a copy image is processed by the scanner 116 and transferred to the image processing unit 112.

  The image processing unit 112 performs various image processes according to each image data, converts the image data for each color, and transfers the image data to the write control unit 101. Each color write control unit 102, 103, 104, 105 of the write control unit 101 generates a print timing for each color, receives image data in accordance with the sub-scanning timing, performs various write image processing, and then performs LD light emission data. , And the LD control units 106, 107, 108, 109 for each color of KMCY perform LD light emission control, and write an image on the photosensitive drums 7K, 7M, 7C, 7Y.

  As shown in FIG. 4, the K color write control unit 102 includes a write image detection unit 140, a misregistration correction pattern generation unit 128, and an LD data output unit 132, and the input image control unit 136 and the preceding stage of the write control unit 102. A line memory 120 is provided. The M color write control unit 103 includes a skew correction processing unit 125, a write image processing unit 141, a misregistration correction pattern generation unit 129, and an LD data output unit 133. 137 and a line memory 121 are provided. The C color write control unit 104 also includes a skew correction processing unit 126, a write image processing unit 142, a misregistration correction pattern generation unit 130, and an LD data output unit 134, and an input image control unit 138 and an upstream stage of the write control unit 104. A line memory 122 is provided. The Y color writing control unit 105 also includes a skew correction processing unit 127, a writing image processing unit 143, a misregistration correction pattern generation unit 131, and an LD data output unit 135, and the input image control unit 139 and the preceding stage of the writing control unit 105 are provided. A line memory 123 is provided.

  That is, skew correction processing units 125, 126, and 127 are provided for each color of MCY, and no skew correction processing unit is provided for K color because skew correction is unnecessary. This is because in this embodiment, the K color is used as a reference color, and the other MCY colors are corrected for misregistration using the K color as a reference.

  When the write control unit 101 is configured as shown in FIG. 4, the image data input from the image processing unit 112 is K color, the image data is written line by line while the line memory 120 is toggled by the input image control unit 136. Send to processing unit 140. The image data processed by the writing image processing unit 140 is transferred to the LD data output unit 132, converted into an LD modulation signal, output to the LD control unit 106, and the LD emits light based on the drive signal of the LD control unit 106. To do.

  For each color of MCY, before the image data is transferred from the input image processing units 137, 138, 139 to the respective writing image processing units 141, 142, 143, the skew correction processing units 125, 126, 127 for each color are respectively transmitted. After input and skew correction, the image data is transferred to each of the write image processing units 141, 142, and 143, and thereafter processed in the same manner as the K color.

  When printing a misregistration correction pattern, the misregistration correction patterns generated by the misregistration correction pattern generation units 128, 129, 130, and 131 for each of the KMCY colors are transferred to the LD data output units 132, 133, 134, and 135. , Converted to LD data, output to the subsequent LD control units 106, 107, 108, 109, and written by the LD of the exposure unit 9.

  FIG. 5 is a flowchart showing a processing procedure of misregistration correction processing for correcting misregistration of each color. Since the misregistration correction process itself is a known or well-known technique as disclosed in, for example, Japanese Patent No. 3556349, description of the misregistration correction process itself is omitted here. The following misalignment correction processing is performed when the reference color is K. The reference color is a color used as a reference for correction, and the positional deviation between the colors is corrected by matching other colors with the reference color.

  When the misregistration correction is started, the misregistration correction patterns generated by the misregistration correction pattern generation units 128 to 131 in the respective color writing control units 102 to 105 in FIG. 4 are formed on the transfer belt 3 (step SA-). 1).

  Next, the detection sensors 15 and 16 detect the correction pattern 14 formed in step SA-1 (step SA-2), and the main scanning magnification correction amount with respect to the reference color, the main scanning registration deviation amount, and the sub-scanning A registration deviation amount is calculated (step SA-3). At the same time, a skew amount with respect to the reference color (K) is calculated (step SA-4), and a divided area width (first area width) in the main scanning direction for performing skew correction corresponding to the maximum image size is calculated. A skew correction position is determined (step SA-5). Then, a skew correction amount (image shift amount) corresponding to each determined skew correction area is calculated (step SA-6).

  The main scanning magnification, the main scanning resist, the sub-scanning resist correction amount obtained in Steps SA-3 to SA-6, the main scanning division area width for skew correction, and the skew correction corresponding to each skew correction area. The amount of information is stored in the RAM 111 or a non-illustrated nonvolatile memory (not shown), and the process is terminated (step SA-7). The correction amount stored in the memory is used as a correction amount at the time of printing until the next misalignment correction process is performed.

  FIG. 6 is a flowchart showing a processing procedure during printing. When a print request is generated, various settings calculated by the misregistration correction in FIG. 5 are performed and printing is started. When correcting the color deviation of the main scanning, the main scanning magnification and the writing timing of the main scanning are corrected. In the main scanning magnification correction, a change in the image frequency based on the detected magnification error amount for each color is applied to the writing control unit 101. Do it. The write control unit 101 includes a device capable of setting the frequency very finely, such as a clock generator using a VCO (Voltage Controlled Oscillator). The writing timing of main scanning is adjusted depending on from which position of the main scanning counter that operates with the synchronization detection signal of each color as a trigger. Further, the color misregistration correction in the sub-scan is performed by adjusting the sub-scan writing timing.

  That is, when there is a print request, setting of the pixel clock frequency of each color (step SB-1), setting of the main scanning delay amount of each color (step SB-2), setting of the sub-scanning delay amount of each color (step SB-3). ) And setting of the skew correction amount of each color with respect to the reference color (step SB-4). Then, after the process of determining the image shift position corresponding to the print image (step SB-5) is executed, the printing is started (step SB-6). Details of the image shift position determination process in step SB-5 will be described later.

  5 and 6 are executed by the CPU 110.

  FIG. 7 is a timing chart of sub-scanning write timing correction when correcting sub-scanning color misregistration. The write control unit 101 counts the number of lines with reference to the start signal (STTRIG_N) from the CPU 110 and outputs a sub-scan timing signal (* _FSYNC_N) to the image processing unit 112. The image processing unit 112 outputs a sub-scanning gate signal (* _IPFGATE_N) with * _FSYNC_N as a trigger, and transfers image data (* _IPDATA [7: 0] _N). When correcting the sub-scanning registration, the sub-scan delay amount (* _Mfcntld) from the start signal is changed according to the detected misregistration amount. Usually, the misregistration amount with reference to K is set to color (M, C , Y) is reflected in the sub-scan delay amount, and the timing of * _FSYNC_N is changed to perform sub-scan alignment. In addition, * shows each color of Y, M, C, and K.

  FIG. 8 is a diagram showing an example when a position deviation correction pattern is detected by the two detection sensors 15 and 16. The correction pattern 14 is detected by the detection sensors 15 and 16, and the obtained signal is converted from analog data to digital data by the pattern detection unit 113, the data is sampled, and the sampled data is stored in the RAM 111. After the detection of the correction pattern 14 is completed, the CPU 110 performs arithmetic processing for calculating various color misregistration amounts (main scanning magnification, main scanning registration, sub-scanning registration, skew) for the stored data, The correction amount of each shift component is calculated from the color shift amount.

For skew correction, first, the skew amount of each color with respect to the K color is obtained. For example, when the right side of the C color image is shifted downward as shown in FIG. 8B, the C color skew amount: KC_Skew is
KC_Skew = KC_R-KC_L
It is obtained like this. However, KC_R indicates the interval between the K and C color patterns on the right side of the drawing, and KC_L indicates the interval between the K and C color patterns on the left side of the drawing.

  9 and 10 are explanatory diagrams showing a skew correction method (a skew correction amount calculation method). In FIG. 9B, when the input image shown in FIG. 9A is output as LD data as it is due to the skew of the scanning beam, the right side is higher on the transfer paper 2 than the input image of FIG. 9A. FIG. 5 shows an image that is shifted by an amount corresponding to three lines (the number of skew lines is three). When the right side image is shifted upward by 3 lines as shown in FIG. 9B, the main scanning is divided into four equal divisions of the skew amount of lines + 1 as shown in FIG. 9C, and FIG. If an image shifted down by one line is output each time it goes to the right, as shown in FIG. 9E, the left and right image positions of each line on the transfer paper 2 become parallel. .

  FIG. 10B shows a case where the right-side image on the transfer sheet 2 is shifted downward by one line with respect to the input image shown in FIG. 10A. As shown in FIG. Is divided into two equal parts, and as shown in FIG. 10 (d), each line is shifted upward by one line as shown in FIG. 10 (d), the right and left of each line on the transfer paper 2 as shown in FIG. The image position becomes parallel.

  11 and 12 are explanatory diagrams showing a bending correction method (bending correction amount calculation method). FIG. 11 shows an example when the misalignment correction pattern is detected by the three detection sensors 15, 16, and 17. The correction pattern 14 is detected by the detection sensors 15, 16, and 17, and the obtained signal is converted from analog data to digital data by the pattern detection unit 113 shown in FIG. 3, the data is sampled, and the sampled data Is stored in the RAM 111. After the detection of the correction pattern 14 is completed, the CPU 110 performs arithmetic processing for calculating various color misregistration amounts (main scanning magnification, main scanning registration, sub-scanning registration, skew or curvature) for the stored data. The correction amount of each shift component is calculated from the color shift amount.

As for the bending correction, the positional deviation correction pattern may be detected by three or more detection sensors, the skew amount may be obtained for each area divided in the main scanning direction, and the skew correction may be performed for each area. For example, when the misregistration correction pattern is detected by the three detection sensors 15, 16, and 17 as shown in FIG. 11A, the skew amount for the K color between the detection sensors 15 and 17, and the detection sensors 17 and 16. Each of the skew amounts for the K color is obtained. When the center of the M color image is shifted downward as shown in FIG. 11B, the bending amount of M color (each skew amount): KM_Ske1, KM_Skew2 is
KM_Skew1 = KM_C-KM_L
KM_Skew2 = KM_C-KM_R
It is obtained like this. However, KM_C is the interval between the K and M color patterns in the center in the figure, KM_L is the interval between the K and M color patterns on the left side in the figure, and KM_R is the interval between the K and M color patterns on the right side in the figure. Show.

  In FIG. 12B, when the input image shown in FIG. 12A is output as LD data as it is due to the bending of the scanning beam, the center is on the transfer paper 2 as compared with the input image of FIG. An image shifted by one line is shown below. When the center image is shifted downward by one line as shown in FIG. 12B, the main scan between LCs is divided into two equal divisions of the number of skew lines between LCs + 1 as shown in FIG. , The main scan between CRs is divided into two equal divisions of the number of skews between CRs + 1, and as shown in FIG. 12 (d), the LCs shift upward by one line each time they go to the right, If the line is shifted down by one line every time it goes to the right side, the left and right image positions of each line on the transfer paper 2 become parallel as shown in FIG.

  Actually, the input image data is sequentially stored in the skew correction line memory, and the skew correction processing units 125 to 127 for each color of MCY switch which line memory data is read in each divided area. 9 (d), FIG. 10 (d), and FIG. 12 (d) are output. Therefore, the address of the division position in the main scanning direction for each color and the sub-scanning + at each division position. Information on whether to shift in the direction or in the negative direction may be obtained.

  As shown in FIG. 9C, if the number of pixels in the scanning direction is 4800 pixels, the shift is performed 3 lines upward from the left end to the right end. Therefore, the 1200th pixel is shifted down 1 line. As shown in FIG. 9D, the first line memory image data is output from 0 to 1199 pixels for the first line, white pixels are output from 1200 pixels to 4800 pixels, and 0 for the second line. The first line memory image data is output from 1 to 1199 pixels, the first line memory image data is output from 1200 to 2399 pixels, and the white pixels are output from 2400 to 4800 pixels. As shown in (e), the left and right image positions can be corrected to be parallel.

  In the case of FIG. 10, contrary to the case of FIG. 9, white pixels are output from 0 to 2399 pixels on the first line as shown in FIG. 10D, and the first line is output from 2400 pixels to 4800 pixels. Repeat the operation of outputting the memory image data, outputting the first line memory image data from 0 to 2399 pixels on the second line, and outputting the second line memory image data from 2400 pixels to 4800 pixels. As shown in FIG. 10E, the left and right image positions can be corrected to be parallel.

  In the case of FIG. 12, assuming that the number of pixels in the scanning direction is 4800 pixels, the shift is performed downward by one line at the center, so that the shift is performed by one line at the 1200th pixel. Then, as shown in FIG. 12D, the first line outputs white pixels from 0 to 1199 pixels, and the first line memory image data is output from 1200 pixels to 3599 pixels, and from 3600 pixels to 4800 pixels. Until then, white pixels are output. In the second line, the first line memory image data is output from 0 to 1199 pixels, the second line memory image data is output from 1200 to 3599 pixels, and the first line memory image data is output from 2400 to 4800 pixels. By outputting data, the output image can be corrected so that the left and right image positions are parallel as shown in FIG.

  The main scanning division position for skew correction in step SA-5 in the flowchart of FIG. 5 is a position obtained by equally dividing the main scanning image size by the number of skew lines +1.

  FIG. 13 is a timing chart showing the timing at the time of skew correction of the line memory. The input image data (* _IPDATA) is sequentially accumulated in the line memory, and the skew correction processing units 125 to 127 switch which line memory data is read in each divided area, generate an output image, and generate an LD. The data (* _LDDATA) is output to the LD control unit 106. The operation of M color and C color in FIG. 13 shows the correction operation of FIG. 9, and the operation of Y color in FIG. 13 shows the correction operation of FIG. In addition, * shows each color of Y, M, C, and K.

  FIG. 14 is a table showing an example of the skew amount of each color based on the K color at the time of sub-scanning 600 dpi. Hereinafter, the relationship between the skew amount and the skew correction amount will be described.

  As shown in FIG. 14, when the skew amount of each color is M color: −110 [um], C color: −130 [um], and Y color: 30 [um] on the K color basis, the sub-scanning resolution is In the case of 600 dpi, M: +3 line, C: +3 line, and Y: −1 line, respectively, as shown in FIG. This shifts by 42.3 [um] by shifting one line, and the skew correction amount divides each deviation amount by the movement amount per line, rounds off the decimal point to a value in an integer unit, Is a value obtained by inverting.

  The image shift division candidate positions for skew correction in step SA-6 in the flowchart of FIG. 5 are determined in advance according to the main scanning size of the dither matrix used for dither processing. The image division candidate position (image shift candidate position) in step SA-6 in FIG. 5 will be described below.

  In general, since it is difficult for a laser printer to obtain various numbers of gradations, dithering is used to express the number of gradations greater than the number of output gradations of the laser printer. In particular, a color laser printer has a dither matrix corresponding to the number of bits of image data or the resolution for each color, for photographs / characters, in order to express smooth gradation. These dither matrices often have different sizes and shapes. The dithering process is a process for expressing a multi-tone image in binary and superimposing a matrix called a dither matrix composed of N × N pixel thresholds on the original image to binarize the pixels. FIG. 16 is an explanatory diagram showing an example of the dither processing. In this example, each pixel of the original image shown in FIG. 16B is compared with the threshold value at the corresponding position in the dither matrix shown in FIG. 16A, and if the gradation of the pixel of the original image is larger, that pixel is selected. The output pixel is set, and if it is small, it is set as a non-output pixel. Thereby, the original image shown in FIG. 16B is converted into the image shown in FIG. Similarly, when a dither process is performed on the original image shown in FIG. 16D by the dither matrix shown in FIG. 16A, the original image is converted as shown in FIG. Since the individual pixels (dither matrix) are very small, the matrix shown in FIGS. 16C and 16E appears as different gradations to the human eye. By performing such processing, dither processing is processing that expresses multiple gradations using binary values. There is also a multi-value dither process in which the number of output gradations used in the dither process is not a binary value but a multi-gradation of about 3 to 16 gradations.

The relationship between the image correction division candidate position for skew correction and the dither matrix is as follows.
Since the reference color for skew correction does not shift the image, the dither matrix for the reference color is excluded. In addition, since skew correction is performed for each color, image shift division candidate positions are determined for each color dither matrix. FIG. 17A shows a dot-concentrated dither matrix in which the dither matrix DMX grows in a circular shape from the center of the matrix. Here, as shown in FIG. 17B, when the image shift by the skew correction as described with reference to FIGS. 9 and 10 is performed in the drawing area in the dither matrix, the dither pattern DPN at the image shift position. The shape changes.

  The adjacency changes in the upper and lower pixels of the dither pattern in FIG. 17B and the dither pattern in FIG. 18A and 18B are enlarged views of a part of the dither pattern in FIGS. 17A and 17B. Although the adjacent pixel A ′ of the pixel A in FIG. 18A before the shift is a black pixel, when the shift process is performed, the dither pattern as shown in FIG. A ′ changes to a white pixel.

  In electrophotographic recording, since the beam diameter of laser light is usually larger than the pixel size, when image data is output, the toner adhesion area in the recorded image (on the printing paper) expands beyond the pixel size. When the pixel adjacency changes as a result of the shift process as in the image image of FIG. 18B, the actual output image is as shown in FIG. 19B. It changes with respect to the output image of the image (FIG. 19A). That is, when the shape change of the dither pattern occurs due to the image shift, the toner adhesion area varies in the recorded image (on the printing paper).

  When this is applied to the entire assembly of the dither matrix DMX, it is as shown in FIG. That is, when image shift by skew correction is performed in the drawing area in the dither matrix, the shape change of the dither pattern occurs only at the image shift position by skew correction. Therefore, a change in the toner adhesion area occurs at the image shift position on the transfer paper 2, and this change frequently occurs in the sub-scanning direction due to the periodicity of dither, so that a noise image is generated and the image quality is deteriorated. . Therefore, as shown in FIG. 21, the image shift candidate position is set to a position that is a multiple of the dither matrix main scanning size. As a result, the image shift position does not come inside the dither matrix, and the image can be shifted without causing a change in the shape of the dither pattern.

  As described with reference to FIG. 21, in this embodiment, in order to prevent the occurrence of image noise due to the collapse of the dither pattern DPN, the shift candidate position is set to a position that is a multiple of the dither matrix main scanning size. This setting is executed in step SA-6 in the flowchart of FIG. That is, until now, as shown in FIG. 22, the image is shifted at the image division position (image shift position) PA calculated in step SA-5, but as described above, the image division calculated in step SA-5. When the image is shifted at the position PA, there is a possibility that the image is shifted at a position where the shape of the dither pattern is changed (a change in the toner adhesion area during output occurs). Therefore, as shown in FIG. 23, among the plurality of image shift candidate positions (PB1 to PB7), an image division candidate position (image shift candidate position) PB3 closest to the image division position PA calculated in step SA-5 is newly set. An image shift position is set, and the image is shifted at that position. Since the size L2 in the main scanning direction of the dither matrix DMX is common to each matrix, when the shift position is moved from the calculated image shift position PA to the adjacent image candidate shift position PB3, the next shift position becomes the image candidate shift position PB6, and the shift is performed. It can be seen that the candidate position PB is a multiple of the dither matrix main scanning size L2. As a result, the image can be shifted without destroying the dither pattern DPN in the dither matrix DMX.

  Since the size L2 of the dither matrix DMX in the main scanning direction is sufficiently small with respect to the image shift interval L1, the image shift position PA calculated in step SA-5 in the flowchart of FIG. 5 should approximate the image shift candidate position PB. Can do.

  Here, details of the skew correction processing units 125 to 127 will be described. FIG. 24 is a block diagram illustrating a configuration of the skew correction processing unit (M) 125 of the skew correction processing units 125 to 127.

  In the skew correction processing unit (M) 125, image data (RAMDATA 0 to 7) input from a plurality of line memories is selected by the data selector 201 and output to the write image processing unit 141. Which line is selected and output from the plurality of line memories by the data selector 201 is determined by a skew correction area signal from the skew correction area control unit 202 and an image shift amount corresponding to each skew correction area.

  The skew correction area control unit 202 outputs a skew correction area signal corresponding to the actual print image based on the skew correction shift position at the maximum image size obtained in the positional deviation detection process. The operation of the skew correction area control unit 202 will be described with reference to the timing chart shown in FIG.

  The skew correction start position determination unit 203 first determines a start position for performing skew correction based on the skew correction start position setting (sk_start), and the first skew correction area output unit 205 determines the first skew from the skew correction start position. The correction area signal (sk_area1) is switched to area 1.

  The skew correction area counter 204 starts counting from the skew correction start position, and thereafter repeats counting for the first skew correction area width setting (sk_wd1) determined in SA-5 of FIG. The first skew correction area output unit 205 switches the first skew correction area signal (sk_area1) to the next area when the skew correction area counter 204 is reset.

  The dither start position determination unit 206 counts the number of pixels from the time when the image area signal (lgate_n) is enabled, and operates the dither area counter 207 when the dither start position is set (dit_start). The dither area counter 207 outputs det_sel and resets it when it matches the second skew correction area width setting (sk_wd2), and repeats the following operations.

  When the image area signal (lgate_n) is disabled, the second skew correction area output unit 208 outputs the first skew correction area signal 1 (sk_area1) as it is to the second skew correction area signal 2 (sk_area2). In the period in which the image region signal (lgate_n) is enabled, the state of the first skew correction area signal 1 (sk_area1) is loaded to the second skew correction area signal 2 (sk_area2) only when the date_sel is output. . In the dither start position setting (dit_start), the position of the dither generation origin position of FIG. 29, which will be described later, from the right end of the sheet is acquired by setting information from a printer controller or the like performing the dither process.

  Further, in the second skew correction area setting 2 (sk_wd2), the main scanning size of the dither matrix used for the print images of FIGS. An integer multiple (Q1 and Q2) of the least common multiple is calculated and set.

  As a result of the above operation, skew correction processing (image shift) is performed by switching the second skew correction area signal 2 (sk_area2) in the image area (matching the above-described image shift position PB). The generation of image noise is eliminated.

  FIG. 25B shows an example in which the image size is smaller than that in FIG. 25A, where the dither generation origin position is different even though the matrix size is the same as in FIG. In this case, if only the dither start position setting (dit_start) is changed and the other parameters are the same as those in FIG. 25A, the second skew correction area signal 2 (sk_area2) is always switched (described above). The skew correction process (image shift) can be performed at the image shift position PB. Various image sizes and dither matrices can be supported by image shift position determination processing described later.

  In FIG. 26, the first skew correction area width setting 1 (sk_wd1) is set to an integer multiple of the least common multiple of the dither matrix size to be used, and is set to the same setting as the second skew correction area width setting 2 (sk_wd2). This is an example of the case. Even in this case, the same operation and effect can be obtained, but since the information acquired at the time of printing is only the dither generation origin position, the control becomes easier.

  FIG. 27 is a timing chart for explaining an operation of setting a skew correction area during mirroring, which will be described later. FIG. 27A shows an operation when there is no mirroring (M color), and FIG. 27B shows an operation when there is mirroring (C color).

In the case of mirroring, the skew correction start position setting (sk_start) in FIG. 24 is set for mirroring by an optical mechanical layout so that the images match when the images are matched even when the scanning direction is reversed. I do. The first skew correction area width setting 1 (sk_wd1) and the second skew correction area width setting 2 (sk_wd2) are the same as those without mirroring, but the dither start position setting (dit_start) is Thus, the skew correction position (shift position) can be set to the same position as when no mirroring is performed.
(Paper size-dither generation origin position) / (Q1 or Q2) remainder

  Next, the image shift position determination process in step SA-5 in FIG. 5 will be described. FIG. 28 is a flowchart illustrating a shift position determination processing procedure executed by the skew correction units 125 to 127.

When determining the shift position, first, the skew amount KY_Skew, KM_Skew, KC_Skew (skew_gap) of each color (YMC color in this embodiment) with respect to the reference color (K color in this embodiment) is detected, and the detected skew amount. Skew_line_gap obtained by converting the above into a line unit based on the sub-scanning resolution (step SC-1). The skew amount skew_line_gap is
skew_line_gap (μm / number of lines) = skew_gap / (25.4 / sub-scan resolution (dpi) * 1000)
(Skew_line_gap is an integer, rounded up to the nearest decimal point)
It becomes. Next, a temporary image shift position PA (_shift_x) for performing skew correction using skew_line_gap and the main scanning size L (xsize) of the image to be formed is
_shift_x = n * xsize / (skew_line_gap + 1)
(However, 0 <n <a + 1 (n is an integer), shift_x is an integer, and the value after the decimal point is rounded down)
(Step SC-2).

After calculating the temporary image shift position PA, the main scanning size L2 (dit_size) of the dither matrix DMX used for the image to be formed is read (step SC-3). Then, the image shift candidate position PB is calculated (step SC-4). Then, it is checked whether or not the temporary image shift position PA and each of the plurality of image shift candidate positions PB are equal, that is, whether or not they match (step SSC-5). If they are equal as a result of the comparison (step SC-7), the image shift position is determined to be a temporary image shift position PA (that is, PB).
On the other hand, when the temporary image shift position PA is different from the image shift candidate position PB, the image shift candidate position PB is determined based on a multiple of the dither matrix size (main scanning size of the dither matrix), and this image shift candidate position PB is set as the image shift position (step SC-8). That is, the temporary shift position shift_x is set as the image shift position as it is.
For example, if the temporary image shift position PA (_shift_x) is not a multiple of the main scan size L2 (dit_size) of the dither matrix DMX used for the image formed, the image shift position shift_x is set.
shift_x = m * dit_size
(Where m is an integer)
Set to.

  Then, the image is shifted at the obtained image shift position shift_x, and the skew is executed (step SC-8).

  FIG. 29 is an explanatory diagram of the origin position of the dither matrix. The dither matrix DMX is drawn with the origin O as a reference, and is periodically and repeatedly arranged in the main scanning direction and the sub-scanning direction, respectively. In many cases, the dither matrix DMX writes an image from the left to the right with the upper left corner of the image drawing area as the origin. As shown in FIG. 29, the left end of the image drawing area is a dither matrix start position in the main scanning direction in a plurality of dither matrices. Here, dither matrices DMXA and DMXB having different sizes are used. The main scanning sizes of both are L2A and L2B, and the state is “L2A <L2B”.

  FIG. 30 shows a setting example of image shift candidate positions PB for skew correction in the case of a plurality of dither matrices DMXA and DMXB configured by a dot-concentrated matrix that grows circularly from the center of the matrix. FIG. When the main scanning direction image shift candidate position PB is set to an integer multiple Q1 of the least common multiple of the main scanning sizes L2A and L2B of the plurality of dither matrices DMXA and DMXB, the dither matrices DMXA and DMXB at the shift position PB are obtained even if the image is shifted. Since there is no change, the generation of a noise image in the image shift unit can be prevented. Note that FIG. 30 shows an example in which two types of dither matrixes are used. Similarly, when three or more types are used, the image shift position is an integer multiple of the least common multiple of main scanning sizes corresponding to the dither matrix types. To do.

  FIG. 31 is a diagram showing a setting example of image shift candidate positions when the dither matrix DMX is configured by a sub-matrix SDMX having a periodic configuration in the main scanning direction. When an integer multiple Q2 of the least common multiple of main scanning cycle widths L3A and L3B of each of a plurality (two types) of sub-matrices SDMXA and SDMXB is set as a skew correction main-scanning direction image shift candidate position PB, the image is shifted. However, since the shift position becomes the boundary between the sub-matrices SDMXA and SDMXB, the dither pattern does not change at the shift position. Therefore, as shown in FIG. 32, even when the image shift is executed at the shift position shown in FIG. 31, generation of a noise image in the image shift unit can be prevented. Further, since the main scanning period widths L3A and L3B of the sub-matrices SDMXA and SDMXB are equal to or smaller than the main scanning sizes L2A and L2B of the dither matrices DMXA and DMXB, the image shift candidate positions for skew correction are the main scanning sizes of the dither matrices DMXA and DMXB. It can be set at a shorter interval than the integral multiple Q1 of the least common multiple of L2A and L2B.

  Further, when the entire image is constituted by a single submatrix SDMX having a periodic configuration in the main scanning direction, if the submatrix main scanning period width L3 is set as a main scanning direction image shift candidate position for skew correction, The image can be shifted without changing the dither pattern DPN.

  FIG. 33 is a diagram showing another example of image shift position setting. When the dither matrices DMXA and DMXB are formed by the dither matrix DMX in which the dither pattern DPN ′ grows across the start positions of the dither matrices DMX1 and DMX2, as shown in FIG. The reference point PBBP of PB is set to a position (Q1 + α) shifted from the left end of the image drawing area to a main scanning position α having no dither pattern in common with a plurality of (in this case, two) dither matrices DMXA and DMXB. The division interval L1 (image shift interval) in the scanning direction is set to an integer multiple Q1 of the least common multiple of the main scanning sizes L2A and L2B of the plurality of dither matrices. As a result, the shift candidate position PB can be set at a position without a dither pattern, and the image can be shifted without changing the dither pattern DPN. Note that α is set smaller than the dither matrix main scanning size in which the dither matrix main scanning sizes L2A and L2B are the smallest. Alternatively, it is set smaller than the greatest common divisor of the plurality of dither matrix main scanning sizes L2A and L2B.

  FIG. 34 shows a configuration in which the dither matrices DMXA and DMXB are composed of sub-matrices SDMXA and SDMXB that are periodic in the main scanning direction, and is configured by a matrix DMX in which the dither pattern DPN ′ grows beyond the dither matrix start position. It is a figure which shows the example of a setting of the image shift candidate position. In this case, the sub-matrixes SDMXA and SDMXB are derived from the reference point PBBP of the image shift candidate position shifted from the left end of the image drawing area to the main scanning position α where there is no image in common with a plurality of (in this case, two) dither matrices DMXA and DMXB. Is set to an integer multiple of the least common multiple of the main scanning cycle widths L3A and L3B. As a result, the image shift candidate position PB can be set at a position without a dither pattern.

  Further, when the entire image is composed of a dither matrix that grows beyond the start position of a single dither matrix, the reference point PBBP for the image shift candidate position in the main scanning direction for skew correction is set to a plurality of dithers from the left end of the image drawing area. In common with the matrices DMXA and DMXB, the position is shifted to the main scanning position α where there is no image, and the division interval in the main scanning direction of the image shift is a periodic configuration in the main scanning size L2 of the dither matrix or in the main scanning direction. Image shift candidate positions PB are set in the main scanning cycle widths L3A and L3B of the dither matrix.

  In the case of a tandem type color laser printer, there is a system configuration in which writing is performed from the rear end in the main scanning direction by color. FIG. 35 is a diagram showing this system configuration called mirror processing. Since the line memories 120 to 123 shown in the writing control unit 101 in FIG. 4 store one line of image data on the basis of the main scanning direction, writing is performed from the rear end in the main scanning direction as shown in FIG. The image data is read from the final position of the line memories 120 to 123 and written from the rear end in the main scanning direction. Such a process is called a mirror process.

  FIG. 36 is a diagram illustrating an example of setting image shift candidate positions when mirror processing is performed. When mirror processing is performed, an image is written from the right to the left of the image drawing area. At this time, the origin O of the dither matrix DMX is often present at the upper left corner of the image drawing area, as in the case where the mirror process is not performed. Therefore, the remainder of the least common multiple of the dither matrix main scanning sizes L2A and L2B for the main scanning size L of the drawing area is β, and the position shifted by β from the right end of the image drawing area in the main scanning direction. The reference point PBBP of the image shift candidate position PB is used. By setting the image shift candidate position PB from the image shift reference point PBBP to an integer multiple Q1 of the least common multiples of the main scanning sizes L2A and L2B of the dither matrices DMXA and DMXB, a position without an image is skew-corrected in the main scanning direction. The image shift candidate position PB can be set, and the image shift can be performed without changing the dither pattern DPN. At this time, the remainder β is set to a value smaller than an integer multiple Q1 of the least common multiple of the dither matrix main scanning sizes L2A and L2B and the main scanning cycle widths L3A and L3B.

  Further, when the dither matrices DMXA and DMXB are configured by sub-matrices SDMXA and SDMXB having a periodic configuration in the main scanning direction, the minimum of the plurality of sub-matrix main scanning cycle widths L3A and L3B with respect to the main scanning size of the drawing area Let the remainder of the integral multiple Q1 of the common multiple be β, and the position shifted by β from the right end of the image drawing area be the reference point PBBP of the division candidate position PB in the main scanning direction.

  FIG. 37 shows an example of setting skew correction main scanning direction shift candidate positions when mirroring processing is performed on an image constituted by the sub-matrices SDMXA and SDMXB in which the dither pattern DPN ′ grows beyond the start position of the matrix. FIG. In this case, the reference point PBBP for image shift is set by β and α (β−α), and the division interval L1 in the main scanning direction of the image shift is set to the main scanning sizes L2A and L2B of the plurality of dither matrices DMXA and DMXB, or A shift candidate position is set at a position where there is no image by setting it to an integral multiple Q2 of the least common multiple of the main scanning cycle widths L3A and L3B of the sub-matrices SDMXA and SDMXB having a periodic configuration in the scanning direction. Accordingly, the second shift position PB from the rear end in the main scanning direction is an integer multiple Q2 + (β−α) position of the least common multiple of the period width.

  Depending on the type of dither matrix, there is a type of matrix in which a noise image is less likely to occur when shifting the image, regardless of the position of the image shift position for skew correction (for example, there is no periodicity like the error diffusion method). Halftone processing method). In such an image, it is good also as a structure which does not implement control for determining an image shift candidate position.

  Depending on the type of dither matrix, there is a dither matrix that generates a noise image only in a specific image shift direction. In such a dither matrix, control is performed to determine the image shift candidate position only when the image is shifted in a direction in which noise is likely to occur. It is good also as a structure which does not implement control matched to size.

  FIG. 38 is a diagram showing a state of a line angle (screen angle) in the line-type dither matrix DMX. In the line-type dither matrix DMX as shown in FIG. 38, there is a dither matrix having a screen angle that is likely to generate a noise image when the image is shifted by the line angle (screen angle). In such a dither matrix, the control for determining the image shift candidate position is performed only when the angle matrix where noise is likely to occur is used, and the shift position when the angle matrix where noise is unlikely to be used is used. It is good also as a structure which does not implement control which adjusts to a matrix size.

  In addition, in the line dither matrix DMX, there is a dither matrix having a number of lines that easily generates a noise image when the image is shifted depending on the number of lines. In such a dither matrix, control is performed to determine the image shift candidate position only when the image is shifted in a direction in which noise is likely to occur, and in the case of shifting in a direction in which noise is not likely to occur, the shift position is set to the matrix size. It is good also as a structure which does not implement control matched to.

  The above is an example of the image shift candidate position setting method, and the setting method changes depending on the combination of the types of dither matrices constituting the entire image.

  FIG. 39 is a diagram showing a setting example of image shift candidate positions when the entire image is composed of a dot-concentrated dither matrix and the dither matrix having a periodic configuration in the main scanning direction. As shown in FIG. 39, a first dither matrix (dither A) DMXA in which the entire image is a dot concentration type and a second dither matrix (dither B) DMXB in which the dither matrix has a periodic configuration in the main scanning direction. If configured, the image shift candidate position is set at an integer multiple of the least common multiple of the main scanning sizes of the dither matrix DMX, or the least common multiple of the main scanning cycle widths of the sub-matrices constituting the dither matrix Image shift candidate positions were set at integer multiple positions. This is as described above. However, it is also possible to set the image shift candidate position by setting an integer multiple of the least common multiple between the main scanning period width L3 of the sub-matrix and the main scanning size L2 of the dither matrix DMX. FIG. 39 shows the state at this time, and is the minimum of the main scanning period width L3B of the first dither matrix (dither A) DMXA main scanning size L2A and the second dither matrix (dither B) DMXB sub-matrix SDMXB. An image shift candidate position PB is set at a position of an integral multiple Q3 of the common multiple. Even when this position is set, the image shift position does not overlap the dither pattern. Therefore, the dither pattern does not collapse and image quality deterioration at the time of image output at the image shift position does not occur.

  The division position and division interval in the main scanning direction are set by setting a target dither matrix according to any of matrix type (type), image shift direction, dither matrix screen angle, and screen line number, Or it changes and this setting is performed for every color. In this embodiment, since the skew color reference color is K, the division position and division interval in the main scanning direction are not set for the skew correction reference color.

As described above, according to the present embodiment, the following effects can be obtained.
1) When performing skew correction by image processing, the image shift position is set according to the dither matrix, so that it is possible to prevent the generation of a noise image due to a change in the dither pattern at the image shift position.

2) When performing skew correction by image processing, the image shift position is set at a position where the collapse of the dither pattern is minimized even if the image shift position in the main scanning direction is shifted, so that the noise image at the image shift position is set. Occurrence can be prevented. It should be noted that when the dither pattern collapse is minimal, the dither pattern collapse is “0”, and there is no image collapse where no dither pattern collapse occurs, and of course no noise image is generated.

3) When performing skew correction by image processing, the division position and division interval in the main scanning direction of image shift are set according to the preset main scanning size of the dither matrix, so that the main scanning size of the dither matrix is divided. Thus, the division position and the division interval can be easily set.

4) When performing skew correction by image processing, the division position and division interval of the image shift in the main scanning direction are set according to the main scanning cycle width of the sub-matrix in the dither matrix set in advance. If the main scanning period width of the sub-matrix is known, the division position and the division interval can be easily set.

5) When using a plurality of types of dither matrices, the main scanning size between the dither matrices to be used, the main scanning cycle width between the sub-matrices, the main scanning size between the dither matrix and the sub-matrix and the main scanning cycle width Since the shift position is set at the least common multiple position, even when different dither matrices are used, it is possible to reduce image quality degradation during image output.

  In FIG. 29, the origin position of the dither matrix is fixed. However, if skew correction is performed by rotating an image having a different origin position of the dither matrix or after dither processing and performing skew correction, the origin is shifted and image corruption occurs. May occur. For this reason, even when the origin position of the dither matrix is shifted, it can be configured to prevent image collapse.

  FIG. 40 is a flowchart showing the procedure of the image shift position determination process according to this modification. First, the number of image data in the main scanning direction (number of main scanning image data) is acquired (step SC-11). Then, the type of dither processing, the main scan size of the dither matrix (dither matrix size), the origin position of the dither processing, and rotation information (0 °, 90 °, 180 °, 270 °) are acquired (step SC-12). Then, the origin position of the dither process is set to the skew correction start position in the image area (step SC-13). Next, a multiple of each dither matrix is set to the skew area width (second area width) in the image area (step SC-14).

  In step SC-12, the setting of the dither start position (dit_start) is performed as follows. In the normal case shown in FIG. 41, assuming that the upper right of the paper size (image size) is the coordinates (0, 0) and the dither origin position information is the coordinates (X1, Y1), X1 is set as it is in the pit_start. .

  As shown in FIG. 42, when the image is shifted to the right side by the printer controller after the dither processing, the upper right of the paper size (image size) is the coordinate (0, 0), and the dither origin position information is the coordinate (X2, Y2). Then, X2 is set as it is in the “dit_start”.

  As shown in FIG. 43, when the printer controller rotates the image 90 ° after the dither processing, the upper right of the paper size (image size) is the coordinate (0, 0), and the dither origin position information is the coordinate (X3, Y3). ), Assuming that the main scan image size is T2, the dither matrix size is the main scan size: L2A, and the sub-scan size is S2A, the remainder of (T2-X3) / S2A is set in dit_start.

  As shown in FIG. 44, when the printer controller rotates the image 180 ° after dithering, the upper right of the paper size (image size) is the coordinate (0, 0), and the dither origin position information is the coordinate (X3, Y3). ), Assuming that the main scanning image size is T1, the dither matrix size is the main scanning size: L2A, and the sub-scanning size is S2A, the remainder of (T1-X3) / L2A is set in pit_start.

  As shown in FIG. 45, when mirroring is performed by the engine control unit in a normal case, the upper right of the paper size (image size) is set to coordinates (0, 0), and the dither origin position information is coordinates (X1, Y1), Assuming that the main scanning image size is T1, the dither matrix size is the main scanning size: L2A, and the sub-scanning size is S2A, the remainder of (T1-X1) / L2A is set in pit_start.

  As shown in FIG. 46, when shifting to the main scanning position α where there is no image in the normal case, the upper right of the paper size (image size) is the coordinates (0, 0), and the dither origin position information is the coordinates (X1, Y1) Assuming that the main scanning image size is T1, the dither matrix size is the main scanning size: L2A, and the sub-scanning size is S2A, X1 + α is set in pit_start.

  By performing such an image shift position determination process, it is possible to prevent image collapse even when the origin position of the dither matrix is shifted.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a perspective view of a transfer belt and a photosensitive drum showing a state in which a correction pattern for correcting misregistration is formed on the transfer belt. It is a block diagram which mainly shows the engine control part which performs writing control and position shift correction in this embodiment. FIG. 4 is a block diagram illustrating details of a write control unit in FIG. 3. It is a flowchart which shows the process sequence of the position shift correction process which corrects the position shift of each color. It is a flowchart which shows the process sequence at the time of printing. 10 is a timing chart of sub-scanning write timing correction when correcting sub-scanning color misregistration. It is a figure which shows an example when detecting a position shift correction pattern with two detection sensors. It is explanatory drawing which shows one method of a skew correction method (skew correction amount calculation method). It is explanatory drawing which shows the other method of a skew correction method (skew correction amount calculation method). It is a figure which shows a state when detecting a position shift correction pattern with three detection sensors. It is explanatory drawing which shows one method of the bending correction method (bending correction amount calculation method). It is a timing chart which shows the timing at the time of skew correction of a line memory. It is a figure which shows an example of the skew amount of each color of K color reference | standard at the time of subscanning 600 dpi in a table | surface form. It is a figure which shows the other example of the skew amount of each color of K color reference | standard at the time of sub-scanning 600 dpi in a table format. It is explanatory drawing which shows an example of a dither process. It is a figure which shows the state of the dither matrix (dither pattern) at the time of performing image shift in the drawing area | region in a dither matrix. It is the figure which expanded a part of dither pattern of Drawing 17 (a) and (b). It is a figure which shows the actual output image of the pattern of FIG. It is a figure which shows the state spread on the aggregate | assembly of the dither matrix of FIG. It is a figure which shows a state when the image shift candidate position at the time of skew correction | amendment of FIG. 20 is set to the position of the multiple of a dither matrix main scanning size. It is a figure which shows the example of the calculated image shift position in the case of performing skew correction. It is a figure which shows the relationship between the image shift candidate position and image shift position in this embodiment. It is a block diagram which shows the structure of a skew correction process part. It is a timing chart of each signal of a skew correction area control part. It is a timing chart of each signal of a skew correction area control part. It is a timing chart of each signal of a skew correction area control part. It is a flowchart which shows the process sequence of the shift position determination performed with a skew correction part. It is explanatory drawing about the origin position of a dither matrix. It is a figure which shows the example of a setting of the image shift candidate position of the main scanning direction of skew correction when a dither matrix is comprised by the dot concentration type matrix. It is a figure which shows the example of a setting of the image shift candidate position in case the inside of a dither matrix is comprised by the submatrix which becomes a periodic structure in the main scanning direction. It is a figure which shows that generation | occurrence | production of the noise image in an image shift part can be prevented when an image shift is performed. It is a figure which shows the other example of the image shift position setting in this embodiment. It is a figure which shows the example of a setting of the image shift candidate position in case a dither matrix is comprised by the periodic submatrix in the main scanning direction, and is comprised by the matrix which a dither pattern grows over a dither matrix start position. It is a figure which shows the example of the system configuration | structure of the mirror process which writes in from the rear end of a main scanning direction with a color. It is a figure which shows the example of a setting of the image shift candidate position in the case of performing a mirror process. It is a figure which shows the example of a setting of the main scanning direction shift candidate position of a skew correction in the case of performing a mirroring process with respect to the image comprised by the submatrix which a dither pattern grows beyond the starting position of a matrix. It is a figure which shows the state of a line angle (screen angle) in a line-type dither matrix. It is a figure which shows the example of a setting of an image shift candidate position when the whole image is comprised by the dither matrix of a dot concentration type | mold, and the dither matrix which has a periodic structure in the main scanning direction. It is a flowchart which shows the process sequence of the modification of image shift position determination. It is explanatory drawing of the other example about the origin position of a dither matrix. It is explanatory drawing of the other example about the origin position of a dither matrix. It is explanatory drawing of the other example about the origin position of a dither matrix. It is explanatory drawing of the other example about the origin position of a dither matrix. It is explanatory drawing of the other example about the origin position of a dither matrix. It is explanatory drawing of the other example about the origin position of a dither matrix.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image creation process part 2 Transfer paper 9 Exposure machine 15,16 Detection sensor 120,121,122,123 Line memory 125,126,127 Skew correction process part 128,129,130,131 Misalignment correction part DMX, DMXA, DMXB Dither matrix SDMX, SDMXA, SDMXB Sub-matrix L2, L2A, L2B Main scan size L3, L3A, L3B Scan period width PA Calculated image shift position PB1-PB7 Division candidate position PB Image shift position PBBP Reference for starting division of division candidate positions point

Claims (10)

An image correction device,
Based on the main scanning size that is the size of the dither matrix in the main scanning direction used for the dither processing and the distance between the image patterns of the dither matrix, the position where the image pattern does not exist is calculated, and the calculated position is calculated as the input image. A first calculation unit that determines a plurality of image shift candidate positions at the time of skew correction processing for
A second calculation unit that calculates an image division position at the time of performing skew correction processing from a deviation amount of the correction target color with respect to the reference color;
A comparison unit for comparing the image shift candidate position and the image division position;
A determination unit that determines a position closest to the image division position from among the plurality of image shift candidate positions as an image shift position that is a division position in a main scanning direction during skew correction processing;
A correction unit that performs a skew correction process on the input image based on the determined image shift position;
An image correction apparatus comprising:   The image correction apparatus according to claim 1, wherein the first calculation unit calculates a position corresponding to an integer multiple of the main scanning size of the dither matrix as a position where the image pattern does not exist.   When the dither matrix is formed of a plurality of types of patterns, the first calculation unit is a least common multiple of the main scanning size of the first pattern and the main scanning size of the second pattern among the plurality of types of patterns. The image correction apparatus according to claim 1, wherein a position corresponding to an integer multiple of is calculated as a position where the image pattern does not exist.   2. The image correction according to claim 1, wherein the first calculation unit calculates a position corresponding to an integer multiple of the main scanning size of a sub-matrix in the dither matrix as a position where the image pattern does not exist. apparatus.   When the dither matrix exists beyond the start position of the dither matrix, the first calculation unit determines a plurality of reference points of the image shift candidate positions from the front end in the main scanning direction of the image drawing area of the input image. The image correction apparatus according to claim 1, wherein the image correction apparatus sets a position without the image pattern in common with the dither matrix, and determines the image shift candidate position based on the set reference point. The image correction device performs writing from the rear end in the main scanning direction,
The first calculation unit uses the reference point of the image shift candidate position as the reference point of the dither matrix for the size of the image drawing area in the main scanning direction from the rear end in the main scanning direction of the image drawing area of the input image. The image correction apparatus according to claim 1, wherein the image shift candidate position is set at a position shifted by a remainder that is an integral multiple of the least common multiple of the main scanning size, and the image shift candidate position is determined based on the set reference point.   The first calculation unit shifts the reference point from the rear end in the main scanning direction of the image drawing area by a remainder that is an integral multiple of the least common multiple of the plurality of dither matrix main scanning sizes with respect to the main scanning size of the image drawing area. The position is shifted from the position in the main scanning direction of the image drawing area to a position without a dither pattern common to a plurality of dither matrices, and the image shift candidate position is determined based on the set reference point. The image correction apparatus according to claim 6.   When the input image is subjected to a rotation process and the start position of the dither matrix is deviated from the origin position of the image drawing area of the input image, the first calculation unit is a reference point of the image shift candidate position. The image correction according to claim 1, wherein the image shift candidate position is determined based on the rotation angle of the rotation process and the size of the input image, and the image shift candidate position is determined based on the set reference point. apparatus. An image forming apparatus,
Based on the main scanning size that is the size of the dither matrix in the main scanning direction used for the dither processing and the distance between the image patterns of the dither matrix, the position where the image pattern does not exist is calculated, and the calculated position is calculated as the input image. A first calculation unit that determines a plurality of image shift candidate positions at the time of skew correction processing for
A second calculation unit that calculates an image division position at the time of performing skew correction processing from a deviation amount of the correction target color with respect to the reference color;
A comparison unit for comparing the image shift candidate position and the image division position;
A determination unit that determines a position closest to the image division position from among the plurality of image shift candidate positions as an image shift position that is a division position in a main scanning direction during skew correction processing;
A correction unit that performs a skew correction process on the input image based on the determined image shift position;
An image forming unit that performs image forming processing using an image that has undergone skew correction processing;
An image forming apparatus comprising: An image correction method,
Based on the main scanning size that is the size of the dither matrix in the main scanning direction used for the dither processing and the distance between the image patterns of the dither matrix, the position where the image pattern does not exist is calculated, and the calculated position is calculated as the input image. A first calculation step of determining as a plurality of image shift candidate positions during skew correction processing for
A second calculation step of calculating an image division position when performing the skew correction process from a correction amount with respect to the reference color against the target color;
A comparison step of comparing the image shift candidate position and the image division position;
A determination unit that determines a position closest to the image division position from among the plurality of image shift candidate positions as an image shift position that is a division position in a main scanning direction during skew correction processing;
A correction step for performing a skew correction process on the input image based on the determined image shift position;
An image correction method comprising:

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