JP2019008334A - Printing device, control method for printing device, and program - Google Patents

Abstract

To suitably correct an amount of a color shift by visual observation by a user.SOLUTION: A chart allowing user's input of a plurality of adjustment values individually corresponding to a plurality of positions in a main scanning direction is printed.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming technique for performing distortion correction for reducing image distortion.

  When the characteristics of the optical system of an electrophotographic printer engine change due to long-term use, etc., when a different optical system is used for each process color, a printing position shift occurs between the process colors. When the printing position shift between the process colors occurs, the color shift is conspicuous and the quality of the printed image is deteriorated.

  Therefore, Patent Document 1 discloses a technique for correcting color misregistration. The image forming apparatus disclosed in Patent Document 1 prints a chart including an image in which a plurality of parallel line images composed of process colors serving as reference colors and a plurality of stepped images composed of adjustment colors are overlapped. Then, the user visually checks the printed chart and inputs an adjustment value of the printing position deviation between the reference color and the adjustment color. The image forming apparatus suppresses the occurrence of color misregistration by uniformly shifting the print position of the image of the adjustment color based on the input adjustment value.

JP 2014-021357 A

  Depending on the optical system of the electrophotographic printer engine, the laser beam that scans the photoreceptor is curved in the sub-scanning direction or expanded and contracted in the main scanning direction. The degree of bending and expansion / contraction (that is, the degree of printing position deviation in the sub-scanning direction and the main scanning direction) varies depending on the position in the main scanning direction. Therefore, even if the user inputs an adjustment value after viewing the chart in which the images of the reference color and the adjustment color are printed at one position in the main scanning direction, the reference color and adjustment at another position are determined by the adjustment value. It is difficult to suitably correct the color shift between colors.

  The image forming apparatus of the present invention prints a chart in which patterns each including an image object made up of a first process color and an image object made up of a second process color are arranged at a plurality of positions in the main scanning direction. And receiving from the user a plurality of pieces of information related to color misregistration correction between the first process color and the second process color corresponding to each of the plurality of positions based on each pattern arranged in the printed chart And correction means for performing color misregistration correction between the first process color and the second process color based on the received plurality of information.

  ADVANTAGE OF THE INVENTION According to this invention, the function for correct | amending suitably the scanning line distortion which changes according to the position in a main scanning direction can be provided to a user.

1 is a system block diagram of an image forming apparatus. The conceptual diagram of the distortion correction of a subscanning direction. Explanatory drawing of the distortion correction of a subscanning direction. The block diagram of a printer engine. 6 is a chart for correcting distortion information in the sub-scanning direction. 10 is a flowchart for calculating correction information for distortion information in the sub-scanning direction. Input screen for visual color misregistration. The conceptual diagram of distortion of a scanning line. 6 is a chart for correcting distortion information in the main scanning direction. 6 is a flowchart for calculating correction information of distortion information in the main scanning direction.

Example 1
FIG. 1A is a system block diagram of an MFP (Multi Function Peripheral) 100 used as the image forming apparatus of this embodiment. The MFP 100 according to the present exemplary embodiment can perform color printing of four process colors (cyan, magenta, yellow, and black).

  The MFP 100 is connected to a host PC 170 via a LAN (Local Area Network) 160. Host PC 170 transmits PDL (Page Description Language) data, which is print data, to MFP 100 via LAN 160. The MFP 100 rasterizes the received print data to generate image data (bitmap) for each process color. Then, the MFP 100 performs distortion correction (described later) on the generated image data for each process color (FIG. 3), and superimposes and forms images for each process color based on the image data after distortion correction. MFP 100 then prints the final superimposed image on a sheet.

  The MFP 100 according to the present embodiment stores chart image data (predetermined bitmap) in advance. The MFP 100 performs distortion correction on the image data of the chart. Then, the MFP 100 superimposes and forms images for each process color based on the chart image data after distortion correction. MFP 100 then prints the final superimposed image on a sheet. The sheet printed in this way is a chart. This chart is used for correcting (updating) laser distortion information (also simply referred to as distortion information) used for distortion correction. This correction process will be described later.

  The MFP 100 includes a control unit 110, a printer 130, and an operation unit 140.

  The control unit 110 includes a CPU 111, RAM 112, ROM 113, operation unit I / F 114, HDD 115, memory 116, device I / F 117, image processing unit 118, and LAN I / F 119.

  The LAN I / F 119 is an interface that connects the LAN 160 and the control unit 110, and transmits and receives data to and from the external host PC 170 via the LAN 160. Host PC 170 is connected to MFP 100 via LAN 160, and transmits print data to MFP 100.

  An HDD (hard disk drive) 115 stores system software, image data, a program for controlling the operation of the MFP 100, and the like. The HDD 115 stores a program for rasterizing print data and generating bitmap image data for each process color. Further, the HDD 115 stores bitmap image data for each process color for printing a chart to be described later. Further, the HDD 115 stores a program for realizing the processing of the flowchart shown in FIG.

  The CPU 111 comprehensively controls the operation of the MFP 100 and executes processing based on a program stored in the RAM 112 or the HDD 115. A ROM 113 is a boot ROM, and stores a boot program for the MFP 100 system.

  The CPU 111 converts the print data received via the LAN I / F 119 into bitmap image data for each process color by executing a rasterization program stored in the HDD 115. The bitmap for each process color is transmitted to the image processing unit 118 described later, and each image processing is performed.

  The memory 116 stores image data and other data similarly to the HDD 115. As will be described later, a bitmap for each process color before image processing and a bitmap for each process color after image processing are also stored in the memory 116. The bitmap after image processing is transmitted to the printer 130 via a device I / F 117 described later.

  The image processing unit 118 performs image processing on the bitmap for each process color input from the memory 116, and outputs the bitmap after image processing to the memory 116. As image processing, distortion correction for each process color for correcting (reducing) distortion of a printed image is performed.

  The device I / F 117 connects the printer 130 and the control unit 110, and transmits image data from the control unit 110 to the printer 130. At this time, the device I / F 117 serializes the bitmap for each process color stored in the memory 116, and transmits the serialized image data to the printer 130. The device I / F 117 transmits and receives distortion information described later between the control unit 110 and the printer 130.

  The operation unit I / F 114 is an interface that connects the operation unit 140 and the control unit 110, and outputs image data of a screen displayed on the operation unit 140 to the operation unit 140. In addition, the operation unit I / F 114 transmits information (for example, information used for correcting distortion information) input by the user from the operation unit 140 to the CPU 111.

  FIG. 1B shows the configuration of the printer 130. The printer 130 transmits and receives data (distortion information and image data for each process color) to and from the control unit 110 via the device I / F 117.

  The printer 130 includes a printer control unit 210 and a printer engine 220. The printer control unit 210 is connected to the printer engine 220 and controls the printer engine 220.

  The printer control unit 210 includes a CPU 211, a RAM 212, a ROM 213, a control unit I / F 214, a storage unit 215, and an engine I / F 216. The CPU 211 comprehensively controls the operation of the printer 130 and operates based on a program stored in the RAM 212. A ROM 113 is a boot ROM, and stores a boot program for the printer control unit 210. The control unit I / F 214 is connected to the control unit 110 and transmits / receives image data and various information between the printer control unit 210 and the control unit 110.

  The CPU 211 transmits and receives distortion information described later to and from the control unit 110 via the control unit I / F 214.

  The storage unit 215 stores a program and the like for controlling the operation of the printer control unit 210. The storage unit 215 stores correction information described later. When the control unit 110 performs distortion correction, the printer control unit 210 synthesizes (adds) the correction information with distortion information acquired from a ROM (not shown) of the printer engine and transmits the correction information to the control unit 110. For convenience of explanation, the distortion information stored in the ROM (not shown) of the printer engine is referred to as first distortion information, and the distortion information after combining that the printer control unit 210 transmits to the control unit 110 is referred to as second distortion information.

  The engine I / F 216 is connected to the printer engine 220, and the CPU 211 controls the printer engine 220 via the engine I / F 216.

  The printer engine 220 of this embodiment is an electrophotographic printer engine, and includes a laser scanner unit for each process color (cyan, magenta, yellow, and black). FIG. 4 shows a part of the configuration of one laser scanner unit provided in the printer engine 220. In FIG. 4, reference numeral 601 denotes a laser beam irradiation port, reference numeral 602 denotes a rotating polygon mirror (hereinafter referred to as a polygon mirror), reference numeral 603 denotes an fθ lens, and reference numeral 604 denotes a photosensitive member.

  The laser beam irradiation port 601 irradiates a laser beam based on any process color image data received from the control unit 110 via the device I / F 117 and the engine I / F 216. The laser beam irradiated from the laser beam irradiation port 601 is reflected by the polygon mirror 602 and scans the photoconductor 604 through the fθ lens 603. The fθ lens 603 deflects the laser beam scanned at a constant angular velocity by the polygon mirror 602 so as to scan on the photosensitive member 604 at a constant velocity. As will be described later, the printer engine 220 of this embodiment has distortion in the sub-scanning direction (FIG. 8) and distortion in the main scanning direction (FIG. 4) in the scanning of the laser beam. This distortion is different for each laser scanner unit (each process color). As a result, the printing position is shifted between process colors, and color misregistration occurs.

  The printer engine 220 includes a ROM (not shown), and the first distortion information described above is stored in the ROM (not shown). The first distortion information is fixed information representing distortion in the sub-scanning direction and main-scanning direction for each laser scanner unit of the printer engine 220 measured at the factory when the MFP 100 is shipped. The CPU 211 of the printer control unit 210 acquires first distortion information stored in a ROM (not shown) in the printer engine 220 via the engine I / F 216. The CPU 211 of the printer control unit 210 combines the acquired first distortion information with the correction information stored in the storage unit 215 as described above, and sends it to the control unit 110 via the control unit I / F 214. Send.

  FIG. 1C shows the configuration of the image processing unit 118 included in the control unit 110. Each unit shown in FIG. 1C is configured by hardware. The image processing unit 118 includes an acquisition unit 301, a calculation unit 302, a correction unit 303, and an output unit 304.

  The acquisition unit 301 acquires the second distortion information transmitted from the printer 130 via the device I / F 117.

  Based on the acquired second distortion information, the calculation unit 302 calculates a setting value used in distortion correction described later.

  The correction unit 303 performs distortion correction described later on the image data for each process color based on the calculated setting value.

  The output unit 304 outputs the image data subjected to distortion correction to the printer 130 via the device I / F 117.

<Concept of distortion correction in the sub-scanning direction>
As described above, the printer engine 220 of this embodiment has distortion in the main scanning direction and the sub-scanning direction in the scanning of the laser beam. This distortion is caused by an installation error of an optical system such as a polygon mirror or an fθ lens. In view of this, the MFP 100 according to the present embodiment performs distortion correction that absorbs distortion by shifting the pixels of the image data pixel by pixel in the sub-scanning direction in the direction opposite to the distortion in the sub-scanning direction of scanning. For example, if the distortion in the scanning sub-scanning direction is a curve that protrudes upward (a negative direction in the sub-scanning direction), the image data is projected so as to protrude downward (a positive direction in the sub-scanning direction). Curving (actually shifting the pixels in the sub-scanning direction) is performed.

  2A and 2B show the concept of distortion correction performed on image data. FIG. 2A shows input / output image data to the correction unit 303 and a printed image when distortion correction is not performed (through setting). FIG. 2B shows input / output image data to the correction unit 303 and a printed image when distortion correction is performed (during distortion correction). 2A and 2B, the printer engine 220 prints based on the image data input to the correction unit 303 in order from the left, the image data output from the correction unit 303, and the output image data. The image is shown.

  In FIG. 2A, the image data input to the correction unit 303 is a rectangular bitmap. In FIG. 2A, since the distortion correction is not performed on the rectangular image data, the image data output from the correction unit 303 is a rectangular bitmap as with the input. When this output data is printed by, for example, the printer engine 220 having an upward convex distortion, the printed image becomes a rectangular image having an upward convex distortion.

  However, when distortion correction is performed, an image with reduced distortion is printed as shown in FIG. In FIG. 2B, the data input to the correction unit 303 is a rectangular bitmap as in FIG. In FIG. 2B, distortion correction is performed on the rectangular image data. That is, the rectangular bitmap is curved downward (pixel shift). An area 401 indicated by a vertical line pattern in FIG. 2B is invalid image data (white pixel group) given to an area where the original image data does not exist as a result of this bending. The invalid image data is not exposed to the laser beam, so that the print result is not affected. When the image data subjected to distortion correction in this way is printed by the same printer engine 220 as in FIG. 2A, the curvature previously applied to the image data and the distortion of the printer engine 220 cancel each other out. The printed image has reduced distortion. At this time, the invalid image data area 401 corresponds to the area 402 which does not affect the print result.

  The above is the concept of distortion correction performed by the MFP 100 of the present embodiment.

<Distortion correction in the sub-scanning direction>
Details of the distortion correction will be described with reference to FIG. Here, for simplification of description, distortion correction for image data of the magenta process color among the four process colors (yellow, magenta, cyan, black) of the printer engine will be described. Note that the same applies to other process colors.

  FIG. 3A is an example of image data input to the correction unit 303. This image data is a bitmap 500 generated by rasterizing print data. This bitmap 500 is 2 bits per pixel. In this embodiment, 2 bits per pixel, but 1 bit or 4 bits per pixel may be used. The generated bitmap 500 is stored in the memory 116 in order from the address 0x10000000, and one line extending in the main scanning direction of the bitmap 500 includes 640 pixels. Since the bitmap 500 is expressed by 2 bits per pixel, the first line of the bitmap 500 is stored at addresses 0x10000000 to 0x1000009F (160 bytes). Further, the second line, which is one line below the first line in the sub-scanning direction, is stored at addresses 0x100,000A0 to 0x1000013F (for 160 bytes). Similarly, the 3rd to 5th lines are stored in the address of the memory 116 every 640 pixels, that is, 160 bytes. In FIG. 3A, 64 continuous pixels (that is, 16 bytes) form one segment. As will be described below, in the distortion correction of this embodiment, the shift amount in the sub-scanning direction with respect to one segment of 64 pixels is the same.

  First, the acquisition unit 301 acquires the second distortion information from the printer 130 as described above. Then, the calculating unit 302 calculates a distortion correction setting value based on the acquired second distortion information. This calculation method will be described.

  The first distortion information and the second distortion information in this embodiment are three points of information. As described above, the first distortion information is fixed information representing the curve characteristic of the scanning line measured at the factory when MFP 100 is shipped. The second distortion information is information obtained by synthesizing the correction information with the first distortion information, and is obtained by correcting the curve characteristic of the scanning line measured by the improvement with the correction information described later. The three-point information is, for example, positions (X coordinate values) in the main scanning direction and positions (Y coordinate values) in the sub-scanning direction of the three points PL, PC, and PR shown in FIG. The unit for representing the position is, for example, micrometers [μm]. In FIG. 8, the position of the point PL in the main scanning direction and the position in the sub scanning direction are XL and YL, respectively. The coordinates of the point PC are XC and YC. The coordinates of the point PR are XR and YR.

  The calculation unit 302 obtains a quadratic curve y = ax ^ 2 + bx + c that passes through the three coordinates described above. In FIG. 8, a quadratic curve 1101 is shown. This quadratic curve 1101 is the curvature characteristic of the scanning line of the laser beam that the current apparatus considers correct. In order to simplify the calculation, the point PC may be provided at the position of the X coordinate XC = 0 (that is, the center).

  The second distortion information here indicates a positional shift in the sub-scanning direction of the magenta process color image relative to the reference process color image. In this embodiment, the reference color is a yellow process color. That is, the curve 1101 indicates the positional deviation in the sub-scanning direction relative to the reference process color image of the magenta process color image at each position in the main scanning direction in units of μm.

  Then, the calculation unit 302 calculates y (Y coordinate value) by substituting the X coordinate value corresponding to each segment into the variable x of the curve 1101. Since the calculated y is in μm units, the calculation unit 302 converts y into pixel units in consideration of the print resolution in the sub-scanning direction. If the printing resolution in the sub-scanning direction is, for example, 600 dpi, the size (height) of one pixel is about 42 μm, so that y divided by 42 and rounded off is the magenta process color for that segment. Thus, the relative positional deviation of the pixel unit with respect to the reference color. The calculation unit 302 stores the relative positional deviation in units of pixels with respect to each segment thus obtained as a setting value in a register provided in the memory 116. An example of the calculated set value is shown in FIG. In this example, a set value 501 is shown in which an upward segment for one pixel (one line) is read from segment 2, and an upward segment for one pixel (one line) is read from segment 4. Yes.

  Next, an operation in which the correction unit 303 performs distortion correction based on the calculated setting value 501 will be described. The correction unit 303 reads the bitmap 500 stored in the memory 116 while switching the lines to be read according to the set value 501, and writes the corrected bitmap for one line to the address continuing from the address 0x20000000 of the memory 116. return. In this reading, the correction unit 303 refers to the setting value calculated by the calculation unit 302 for each segment, and reads the segment at a position shifted by the number of pixels corresponding to the setting value.

  The result (distortion correction result) of reading out the bitmap 500 from the memory 116 using the set value 501 in FIG. 3B is the bitmap 540 in FIG. The bitmap 540 is written sequentially from the address 0x20000000 of the memory 116. In this bitmap 540, the bitmap 500 is shifted downward by one pixel (one line) from the position of segment 2, and further shifted downward by one pixel (one line) from the position of segment 4. .

  According to the set value 501 shown in FIG. 3B, for example, the reading of the bitmap 500 corresponding to the first line is as follows. For the segments after segment 2, the segment 531 of the invalid image (white pixel group) is read without reading the segment of the address that does not originally exist in the bitmap 500. That is, when there is no segment to be read beyond the upper (or lower) boundary of the bitmap 500, the invalid image (white pixel group) segment 531 is handled as a read result. This invalid image is as described in FIG.

  As described above, the correction unit 303 performs distortion correction, so that the bitmap 540 in which the segment (pixel) included in the bitmap 500 is shifted in the sub-scanning direction according to the set value is written in the memory 116.

  Then, the output unit 304 transmits the corrected bitmap 540 to the printer 130 via the device I / F 117.

  As described above, the above distortion correction is performed on the bitmap for each process color based on the set value calculated for each process color.

<Print chart>
FIG. 5A shows a predetermined bitmap (image data) 700 stored in the HDD 115. This predetermined bitmap 700 is image data of four process colors. Based on this image data 700, a chart used for the user to visually confirm the degree of the printing position shift between the process colors in the sub-scanning direction at three locations in the main scanning direction is printed.

  The bitmap 700 includes nine areas 701 to 709. Each region includes a plurality of lines in the main scanning direction composed of cyan as a reference color and a plurality of lines in the main scanning direction composed of process colors whose relative positions with respect to the reference color are corrected. Each of the regions 701 to 703 includes a plurality of cyan lines and a plurality of yellow lines. Each of the regions 704 to 706 includes a plurality of cyan lines and a plurality of magenta lines. Each of the regions 707 to 709 includes a plurality of cyan lines and a plurality of black lines.

  That is, the cyan line as the reference color is included in all the areas, and in each area, the degree of deviation (coincidence) between the cyan line as the reference color and another process color line is visually confirmed by the user. . The reference color (cyan) used as a comparison source when visually confirming the printing position deviation from other process colors is a color different from the standard color (yellow) used in the above distortion correction. This is to prevent the user from making visual confirmation difficult when yellow is used as a reference color, which has a relatively higher luminance than other colors.

  The regions 701, 702, and 703 are provided at three different positions in the main scanning direction. That is, there are three places, left, center, and right. Information indicating these three different positions is also included in the bitmap 700 and printed as a chart. The same applies to the regions 704 to 706, and the same applies to the regions 707 to 709. Each of the three different positions corresponds to each of the three positions in the main scanning direction included in the second distortion information. It is preferable to arrange the regions 701, 704, and 707 at the position (XL) of the point PL in FIG. 8 in the main scanning direction. In addition, it is preferable to arrange the regions 702, 705, and 708 at the position (XC) of the point PC in the main scanning direction. In addition, it is preferable to arrange the regions 703, 706, and 709 at the position (XR) of the point PL in the main scanning direction. This is because the closer the positions to be visually confirmed by the user in correction of distortion information are closer to the three positions, the higher the accuracy of color misregistration correction based on the correction information is secured.

  Of these, the region 702 will be described with reference to FIG.

  The area 702 includes five patterns including a cyan line and a yellow line. In FIG. 5B, a horizontal line 710 represented by solid color represents a cyan line as a reference color, and a horizontal line 711 represented by diagonal lines represents a yellow line. The numbers in the area surrounded by the broken line 712 indicate the identification number of each pattern. Each pattern has a different distance (distance in the sub-scanning direction) between the cyan line and the yellow line. Each pattern is given a pattern identification number 712 to the left of the pattern, and an identification number is also printed. This identification number is input from the operation unit 140 by the user as a visual color shift amount described later.

  In the pattern corresponding to the identification number “−2” in the area 702, the yellow line 711 is shifted by two pixels upward (negative direction in the sub-scanning direction) with respect to the cyan line 710 that is the reference color. ing. In the pattern corresponding to the identification number “−1”, the yellow line 710 is shifted upward by one pixel with respect to the cyan line 710. In the pattern corresponding to the identification number “0”, the yellow line 711 is arranged without deviation at a position overlapping the cyan line 710. In the pattern corresponding to the identification number “+1”, the yellow line 711 is shifted by one pixel downward (positive direction in the sub-scanning direction) with respect to the cyan line 710. In the pattern corresponding to the identification number “+2”, the yellow line 711 is shifted downward by two pixels with respect to the cyan line 710.

  As will be described later, when printing the bitmap 700 including this region 702, distortion correction is performed by the image processing unit 118 (correction unit 303) using the second distortion information of cyan and yellow. Therefore, if the curve characteristic represented by the second distortion information of cyan substantially matches the curve characteristic of the current scan line, distortion correction is appropriate, so the image of the region 702 in the printed chart is It matches the image of the area 702 included in the bitmap 700. That is, the pattern corresponding to the identification number “0” is printed with the cyan line as the reference color and the yellow line overlapping with the least deviation than the patterns corresponding to the other identification numbers.

  On the other hand, the curve characteristic (1101 in FIG. 8) represented by the second cyan distortion information may not match the curve characteristic (1102 in FIG. 8) of the current cyan scan line. In this case, in a pattern corresponding to an identification number (for example, “−2”) different from the identification number “0”, the cyan line and the yellow line are printed with the least overlap. As shown in FIG. 8, when a shift 1103 corresponding to +2 pixels occurs at the center position between the curve characteristics 1101 and 1102, the actual scan line at the center position is sub-scanned more than the position of the scan line assumed by the apparatus. It passes two pixels above in the direction. That is, the cyan line at the center position in the printed chart is printed two pixels above the yellow line that is the basis for distortion information. The state of the area 702 in the printed chart is shown in FIG. In this case, as can be seen from FIG. 5C, the pattern corresponding to the identification number “−2” is printed with the two lines overlapping with the least deviation. In this case, in the process of the flowchart described later with reference to FIG. 6A, the user inputs the identification number “−2” to the operation unit 140 as the visual color misregistration amount corresponding to the region 702.

  In each of the other regions 701 and 703 to 709, five patterns having different distances between the reference color line and the other process color line are arranged as in the region 702. When the bitmap 700 including other areas is printed, a chart is printed based on the bitmap subjected to distortion correction according to the second distortion information corresponding to each process color. In each region, as in the region 702, the identification number of the pattern in which the reference color and the line of the other color overlap with the most deviation is input to the operation unit 140 by the user.

  In the bitmap 700 of the present embodiment, five patterns from identification numbers “−2” to “+2” are shown, but they may be increased or decreased as necessary.

<Correction of distortion information in the sub-scanning direction>
FIG. 6 shows a processing flow for correcting distortion information in the sub-scanning direction. This flow is established by cooperation between the control unit 110 and the printer control unit 210. The control unit 110 executes processing according to a program stored in the HDD 115. In addition, the printer control unit 210 executes processing according to a program stored in the storage unit 215.

  In step S <b> 801, the control unit 110 and the printer control unit 210 visually check the degree of print position deviation between process colors in the sub-scanning direction based on a predetermined bitmap 700 stored in the HDD 115. To print.

  Details of the processing in step S801 will be described. The CPU 111 of the control unit 110 acquires a predetermined bitmap 700 from the HDD 115 and stores the acquired bitmap 700 in the memory 116. Next, the image processing unit 118 performs distortion correction on the bitmap 700 stored in the memory 116, and transmits the corrected bitmap to the printer control unit 210. The transmission of the bitmap after distortion correction by the image processing unit 118 is specifically performed in the following flow.

  First, the acquisition unit 301 requests distortion information (second distortion information) from the printer control unit 210. Then, the printer control unit 210 acquires the first distortion information from the printer engine, and combines (adds) the current correction information stored in the storage unit 215 to generate the second distortion information. Here, the correction information is information used to correct each of the three coordinate positions included in the first distortion information, and is, for example, three coordinate information corresponding to each of the three points. For example, the coordinate information for correcting the coordinate positions of the points PL, PC, and PR in the first distortion information has contents of ΔL [μm], ΔC [μm], and ΔR [μm] in the sub-scanning direction. That is, if the first strain information is YL [μm], YC [μm], YR [μm], the second strain information is (YL + ΔL) [μm], (YC + ΔC) [μm], (YR + ΔR). [Μm]. The generated second distortion information is transmitted to the acquisition unit 301 by the printer control unit 210.

  As described above, the calculation unit 302 calculates a setting value for each process color based on the second distortion information for each process color acquired by the acquisition unit 301. Then, the correction unit 303 performs distortion correction for each process color on the bitmap 700 stored in the memory 116 based on the calculated setting value, and writes the distortion-corrected bitmap back to the memory 116. Then, the output unit 304 transmits the bitmap after distortion correction to the printer control unit 210 via the device I / F 117.

  The printer control unit 210 prints a chart with the printer engine 220 based on the bitmap after distortion correction transmitted from the control unit 110.

  The above is the printing of the chart based on the bitmap 700.

  Subsequently, in step S802, the operation unit 140 receives an input by the user of the visual color misregistration amount. A method of user input of the visual color misregistration amount will be described with reference to FIG.

  FIG. 7 shows a screen displayed on the operation unit 140. The user visually confirms how the reference color (cyan) line overlaps with other process color lines (yellow, magenta, black) in each of the regions 701 to 709 in the chart printed in step S801. Then, for each region, the user inputs the identification number of the pattern in which the two color lines overlap (match) with the least deviation on the input screen shown in FIG. Regarding the input of the reference color (cyan) and yellow visual color misregistration amounts in FIG. 7, since the identification number corresponding to the condition in the area 701 is “0”, the visual color misregistration amount “0” is displayed in the input field 1001. Is input by. Further, since the identification number corresponding to the condition in the area 702 is “−2”, the visual color shift amount “−2” is input to the input field 1002 by the user. Since the identification number corresponding to the condition in the area 703 is “0”, the visual color misregistration amount “0” is input to the input field 1003 by the user. Similarly, user input is performed for other areas.

  When the input of the visual color misregistration amount is completed for each region and the “OK button” is pressed by the user, the operation unit 140 transmits the input visual color misregistration amount of each region to the control unit 110, and this step S802 ends.

  In step S <b> 803, the control unit 110 transmits a visual color misregistration amount input completion notification to the printer control unit 210. At this time, the control unit 110 may transmit the visual color misregistration amount of each area received from the operation unit 140 to the printer control unit 210, or a shared memory (not illustrated) shared by the control unit 110 and the printer control unit 210. You may memorize.

  In step S804, the printer control unit 210 that has received the visual color misregistration amount completion notification acquires the visual color misregistration amount of each region directly from the control unit 110 or via the shared memory.

  In step S805, the printer control unit 210 stores the acquired visual color misregistration amount in the storage unit 215.

  In step S <b> 806, the printer control unit 210 calculates correction information for each process color from the visual color misregistration amount stored in the storage unit 215. With respect to this calculation method, the visual color misregistration amount input to the input field 1002 corresponding to the area 702 will be described.

  The printer control unit 210 acquires the visual color misregistration amount “−2” of the area 702 input in the input field 1002. This visual color misregistration amount “−2” indicates a deviation in the sub-scanning direction of the yellow printing position with respect to the reference color (cyan). Therefore, a deviation in the sub-scanning direction of the cyan printing position with respect to the reference color (yellow) “+2”. Further, since the visual color misregistration amount is expressed in units of pixels, the printer control unit 210 converts the visual color misregistration amount into μm units that are units of correction information. When the printing resolution is 600 dpi in the sub-scanning direction, one pixel is converted to 42 μm.

  Therefore, the printer control unit 210 obtains (+ 2 × 42) = + 84 [μm] as correction information corresponding to the center position XC for the cyan process color. The printer control unit 210 stores the obtained correction information in the storage unit 215. Correction information is similarly obtained for other regions and other process colors.

  Note that the visual color misregistration amount input for other process colors is information (identification number) of color misregistration of other process colors with respect to the reference color (cyan). For this reason, when obtaining correction information for other process colors, the input for the areas 701 to 703 (color shift information of the reference color (yellow) with respect to the reference color (cyan)) is also used. For example, it is assumed that “−1” is input to the input field 1004 by the user as the visual color misregistration amount for the region 705. In this case, since magenta is further shifted by −1 pixel with respect to cyan that is shifted by +2 pixels with respect to yellow, the color shift with respect to yellow that is the reference color of magenta is + 2-1 = 1 pixel. It becomes. Therefore, “+42 μm” is obtained as magenta correction information for the center position XC corresponding to the region 705.

  In order to avoid such a complicated calculation when obtaining correction information, the reference color may be the same as the reference color.

  In step S <b> 807, the printer control unit 210 acquires first distortion information from the printer engine 220.

  In step S808, the printer control unit 210 calculates second distortion information from the correction information calculated in step S806 and the first distortion information in step S807. As described above, this calculation is performed by combining the first distortion information of the process color to be calculated and the correction information corresponding to the process color.

  In step S809, the printer control unit 210 transmits the calculated second distortion information for each process color to the control unit 110 via the device I / F 117.

  In step S810, the acquisition unit 301 and the calculation unit 302 of the control unit 110 calculate a setting value based on the second distortion information acquired in step S809, and store the setting value in the memory 116 as the latest setting value.

  In step S811, the control unit 110 transmits the setting value calculated in step S810 to the printer control unit 210.

  In summary, in this processing flow, the printer control unit 210 calculates the visual color misregistration amount to the correction information, and calculates the second distortion information from the first distortion information and the correction information. In addition, the control unit 110 calculates a setting value used for distortion correction from the second distortion information.

  The set value obtained from the second distortion information obtained by the above flow is used for distortion correction in printing based on the subsequent print data.

  The above is the distortion information correction processing executed by the MFP 100 according to the first embodiment. The MFP 100 according to the present exemplary embodiment acquires information (identification number) related to correction of color misregistration between the reference color and other process colors at each of three different positions in the main scanning direction, based on user input by visually observing the chart. Then, MFP 100 calculates correction information for correcting distortion information with the acquired information.

  In this embodiment, the user inputs information regarding correction for each of three different positions in the main scanning direction. However, a configuration may be adopted in which information regarding correction is input by a user for each of two or more different positions in the main scanning direction. If the information corresponding to each of the two positions is input, the inclination component (linear function) of the distortion information can be corrected. If the information corresponding to each of the three or more positions is input, the information is more complicated. Can make high amendments to the system.

(Example 2)
In Example 1, correction information of the curve characteristic (shift characteristic in the sub-scanning direction) of the scanning line of the laser beam of each process color was obtained at a plurality of different positions in the main scanning direction. Laser beam scanning line distortion includes expansion and contraction in the main scanning direction. The MFP 110 detects distortion of expansion and contraction in the main scanning direction by inserting a pixel piece (1/16 of the size of one pixel). Correct by thinning. This correction is also performed based on distortion information for each process color relating to expansion and contraction in the main scanning direction. In this embodiment, distortion information for each process color relating to expansion and contraction in the main scanning direction is corrected from user input using a chart in the same manner as in the first embodiment. That is, a chart for visually confirming the color misregistration in the main scanning direction is printed, and the correction is made based on the visual color misregistration input from the user based on the chart.

  In the following description, unless otherwise noted, the configuration is the same as that of MFP 100 according to the first embodiment.

<Distortion correction in the main scanning direction>
First, distortion correction in the main scanning direction will be described.

  FIG. 4 shows a part of the configuration of the printer engine 220 as described above. Strictly speaking, the fθ lens 603 of the printer engine 220 does not scan the photoconductor 604 at a constant speed. That is, the scanning length (exposure length) for one pixel data in one scanning of the laser beam differs depending on the scanning position (position of pixel data in the main scanning direction).

  This will be explained. A section 605 in the main scanning direction is an ideal section in which exposure is performed by one scan of a laser beam when exposing one line of image data from end to end of an image (ideal of one line image). Length). Consider, for example, four sections 606 obtained by dividing the section 605 into four equal parts. Ideally, the length of each section 606 is a quarter of the length of the section 605. Further, considering that the image data of each part obtained by dividing the image data for one line from the end of the image into four equal parts is exposed, the image data of each part divided into four parts is exposed. Should ideally coincide with interval 606.

  However, depending on the fθ lens 603, the laser beam does not scan the photoconductor 604 at exactly the same speed, so the length of the section where the image data of each part divided into four parts is exposed varies from part to part. . For example, in FIG. 4, sections in which the image data divided into four parts are exposed are sections 607, 608, 609, and 610 in order. In FIG. 4, the lengths of the sections 607 and 608 are shorter than the length of the section 606, and the lengths of the sections 609 and 610 are longer than the length of the section 606.

  Therefore, the printer engine 220 according to the present embodiment converts pixel piece data (data having a size of less than one pixel) into an image with a different scaling value for each section so that the length of each section is equal to the section 606. Insert or thin out data.

  Insertion of pixel piece data specifies a pixel corresponding to a position where a pixel piece is to be inserted, and inserts the pixel piece data between the specified pixel and its adjacent pixels with the pixel value as the pixel value of the pixel. That is. When the pixel piece is inserted, the printer engine 220 makes the scanning time of the laser beam based on the specified pixel longer by 1/16 pixel.

  Further, the thinning out of the pixel piece data is to specify a pixel corresponding to a position where the pixel piece is to be thinned out, and to thin out the size of the pixel piece from the pixel. When the pixel piece is thinned out, the printer engine 220 shortens the scanning time of the laser beam based on the specified pixel by 1/16 pixel.

  For example, the printer engine 220 inserts pixel piece data for a total of three pixels for image data corresponding to the section 607, and a pixel for a total of one pixel for image data corresponding to the section 608. Insert one piece of data. The printer engine 220 thins out pixel piece data for a total of one pixel for image data corresponding to the section 609, and a total of three pixels for image data corresponding to the section 610. Thinning out one piece of data. The amount of pixel piece insertion or thinning set for each section is referred to as a scaling value, and is stored in the printer engine 220 in the same manner as the first distortion information in the sub-scanning direction of the first embodiment. This scaling value is stored for each process color as first distortion information in the main scanning direction. As will be described later, correction information in pixel piece insertion / extraction is referred to as a minute scaling value and is distinguished. The minute scaling value is set to “0” for all process colors and all intervals as an initial value, and is stored in the storage unit 215 in the same manner as the correction information of the first embodiment. This correction information is updated in this embodiment.

  By the above process (pixel piece insertion / extraction), the length of each section is matched with the ideal length of the section 606. Note that the scaling factor of each section is a type of distortion information used to correct color misregistration in the main scanning direction, and is set and corrected according to the flowchart of FIG.

<Print chart>
FIG. 9A shows a predetermined bitmap (image data) 900 stored in the HDD 115. The predetermined bitmap 900 is image data of four process colors. Based on this image data 720, a chart used for visual confirmation by the user at three positions (left, center, right) in the main scanning direction is printed. Is done. The bitmap 900 is the same as the bitmap 700 in FIG. 5A except that the lines made up of the process colors are arranged in a direction parallel to the sub-scanning direction. That is, the reference color is cyan. Each of the three regions arranged in the upper stage of the bitmap 900 includes a plurality of pairs of cyan vertical lines and yellow vertical lines. The distance between the vertical lines constituting the pair is different for each pair. Each of the three regions arranged in the middle stage of the bitmap 900 includes a plurality of pairs of cyan vertical lines and magenta vertical lines. The distance between the vertical lines constituting the pair is different for each pair. Each of the three regions arranged in the lower stage of the bitmap 900 includes a plurality of pairs of cyan vertical lines and black vertical lines. The distance between the vertical lines constituting the pair is different for each pair.

  FIG. 9B shows a plurality of vertical line pairs included in an area arranged in the center of the upper stage of the bitmap 900. The line object 910 is a cyan vertical line object, and the line object 911 is a yellow vertical line object. The numbers in the broken line 922 are identification numbers corresponding to the respective pairs, and are also printed on the chart. The identification number “−2” corresponds to a vertical line pair in which a yellow vertical line is shifted by −2 pixels in the main scanning direction with respect to a cyan vertical line. That is, the identification number “N” corresponds to a vertical line pair in which a yellow vertical line is shifted by N pixels in the main scanning direction with respect to a cyan vertical line.

  Based on this bitmap 900, a chart including a plurality of vertical lines is printed. At the time of chart printing, similarly to the bitmap 700 of the first embodiment, the bitmap 900 is also based on distortion information in the main scanning direction of each process color (corresponding to the second distortion information of the first embodiment). Printing is performed after distortion correction in the main scanning direction is performed. In the printed chart, the area shown in FIG. 9B is arranged as shown in FIG. In this case, the vertical line pair corresponding to the identification number “−2” overlaps with the least deviation than the other pairs. That is, the yellow printing position shift at the center position is shifted to the right by two pixels in the main scanning direction from the cyan printing position assumed by the apparatus. That is, the yellow print position at the center position should be corrected so as to be shifted to the left from the current position by two pixels with respect to the cyan print position.

  In order to make such correction, as in the first embodiment, the user visually checks the printed chart, specifies the pair that overlaps most without any deviation among the plurality of vertical line pairs, and sets the identification number of the pair. The amount of visual color misregistration is input to the operation unit 140. Also in the present embodiment, the identification number is input for each area. An example of an identification number input screen in the operation unit 140 is shown in FIG. The screen shown in FIG. 7 described in the first embodiment is an input screen for an identification number for correcting a shift in the sub-scanning direction due to the curvature of the scanning line. This is a screen different from the input screen for the identification number for correcting the direction shift. What is important is that in both the first embodiment and the present embodiment, information for correcting color misregistration at a plurality of positions different in the main scanning direction is input by the user corresponding to each of the plurality of positions.

  For the central position in the printed chart of FIG. 9C, the identification number “−2” is input to the operation unit 140 by the user. A correction information calculation method for correcting distortion information indicating distortion in the main scanning direction from the input identification number (visual color misregistration amount) will be described later with reference to FIG.

<Correction of distortion information in main scanning direction>
FIG. 10 shows a processing flow for correcting distortion information in the main scanning direction. This processing flow is established in the MFP 100 by the cooperation of the control unit 110 and the printer control unit 210. The control unit 110 is realized by the program stored in the HDD 115 being developed in the RAM 112 and executed by the CPU 111, and the printer control unit 210 is developed in the RAM 212 and the program stored in the storage unit 215 is executed by the CPU 211. This is realized.

  In step S <b> 901, the MFP 100 prints a chart based on the bitmap 900. In this printing, the MFP 100 performs distortion correction (pixel piece insertion / extraction) on the bitmap 900 using the first distortion information and the correction information stored in the printer engine 220, as in the first embodiment. Then print the chart. The difference from the first embodiment is that the distortion information used is distortion information in the main scanning direction different from the second distortion information, and the distortion correction is not pixel shift in the sub-scanning direction but pixel piece insertion / extraction. That is. Also, it is different from the first embodiment in that it is not the control unit 110 but the printer control unit 210 that performs pixel piece insertion / extraction using distortion information (magnification value). The distortion information in the main scanning direction used in distortion correction by pixel piece insertion / extraction is the total value of the magnification value stored in the printer engine 220 and the minute magnification value stored in the storage unit 215. Here, for convenience of explanation, “0” is set as the minute scaling value for all process colors and intervals.

  In step S902, the operation unit 140 receives an input of a visual color misregistration amount (identification number) from a user who visually confirms the printed chart. Here, the identification number shown in FIG. 7 is input.

  In step S <b> 903, the control unit 110 receives the visual color misregistration amount from the operation unit 140, and transmits a visual color misregistration amount input completion notification to the printer control unit 210.

  In step S <b> 904, the printer control unit 210 acquires a visual color misregistration amount from the control unit 110 in response to receiving the notification from the control unit 110.

  In step S <b> 905, the printer control unit 210 stores the visual color misregistration amount in the storage unit 215.

  In step S906, the printer control unit 210 calculates a minute scaling value of each process color from the stored visual color misregistration amount. This calculation will be described by taking an example of calculating a cyan minute scaling value.

  The visual color misregistration amount related to the calculation of the minute cyan scaling value is for the upper three areas of the bitmap 900. According to FIG. 7, “0”, “−2”, and “0” in order from the left region are the visual color misregistration amounts between cyan and yellow. That is, although there is no color shift between cyan and yellow at both ends of the image in the main scanning direction, the yellow printing position is two pixels to the right (positive direction in the main scanning direction) of the cyan printing position at the center. It's misaligned. That is, if the cyan printing position is shifted in the main scanning direction (right) by two pixels compared to the yellow printing position, an image without color misregistration can be printed. Here, the reference color is yellow as in the first embodiment. Therefore, in order to insert / extract the pixel pieces with respect to the cyan image data in which the cyan print position having no deviation at both ends is shifted to the right by 2 pixels at the center position with respect to the yellow print position, each of the sections 607 to 610 in FIG. The corresponding corrected scaling value is calculated. That is, pixel piece data for a total of one pixel is inserted into cyan image data corresponding to sections 607 and 608 in FIG. 4, and pixel piece data for a total of one pixel is extracted from cyan image data corresponding to sections 609 and 610. A minute scaling value that is thinned out is calculated. For example, the minute scaling values of cyan corresponding to the sections 607, 608, 609, and 610 are calculated as +3/4 pixel, +1/4 pixel, -4 1/4 pixel, and -3/4 pixel, respectively. The However, it is not limited to this value. The printer control unit 210 performs such a minute scaling value for each of the other process colors with respect to the reference color.

  In step S <b> 907, the printer control unit 210 calculates the final minute magnification value by adding the minute magnification value calculated in step S <b> 906 to the magnification value stored in the printer engine 220. Then, the printer control unit 210 sets a final scaling value in the storage unit 215. The scaling value set in this way is used when correcting distortion in the main scanning direction during subsequent printing.

  In this flow, the printer control unit 210 is responsible for calculating a minute scaling value, but the present invention is not limited to this.

(Example 3)
In the present embodiment, the calculation flow of correction information (correction information of three-point information) in the first embodiment and the calculation flow of correction information (small scaling value) in the second embodiment are combined.

  First, the MFP 100 calculates the minute scaling value described in the second embodiment. Next, the MFP 100 prints the chart of the bitmap 900 using the final minute scaling value obtained by adding the calculated minute scaling value and the previously stored scaling value. Then, the user looks at this chart, and when the user determines that no color misregistration between process colors has occurred in all areas, the user corrects distortion information in the main scanning direction on the operation unit 140 of the MFP 100 (see FIG. Information indicating that the calculation of correction information has been completed is input. This input is performed, for example, by touching an OK button displayed on the operation unit 140.

  If the OK button is not touched, the MFP 100 performs the correction information calculation flow of the second embodiment again. If the operation unit 140 displays a cancel button and the user touches it, the process ends without updating the correction information in the main scanning direction. In this case, the MFP 100 may or may not execute the correction information calculation flow of the first embodiment.

  When the OK button is touched, the MFP 100 executes the correction information calculation flow of the first embodiment.

  As described above, since the MFP 100 executes the correction information calculation flow according to the second embodiment before the correction information calculation flow according to the first embodiment, the sub-scan is performed after removing the influence of the expansion / contraction distortion of the image in the main scanning direction. It is possible to calculate correction information for the curvature distortion of the image in the direction. As a result, correction information close to the actual curve characteristic of the scanning line can be calculated.

(Other examples)
In the above embodiment, the patterns arranged in the bitmaps 700 and 720 for chart printing are composed of two process color lines. However, other image objects may be used instead of lines. For example, the image object may be a cross object, and may have any shape as long as the degree of deviation (or coincidence) between two process colors can be visually observed.

  The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The printing apparatus according to the present invention includes a storage unit that stores, for each color, bending information indicating a bending of a trajectory on the photosensitive member of light that exposes the photosensitive member, and correction information based on the bending information stored in the storage unit. The image data is read out by changing the reading position of the image data in the sub-scanning direction, and the photoconductor is exposed based on the image data read by the reading means, and the image is printed on the paper. And a first color material for the second color material object, wherein the first color material is a pattern composed of a first color material object and a second color material object. Test image data including a plurality of the patterns having different relative positions in the sub-scanning direction of the object and identification information for each of the patterns. A test image printing unit that reads out the image by the printing unit and prints it on a sheet by the printing unit; and the first color material object of the plurality of patterns in the test image printed on the sheet by the test image printing unit and the A receiving unit that receives an input of the identification information corresponding to the pattern in which the print position in the sub-scanning direction of the pattern of the second color material object matches; the identification information received by the receiving unit; And generating means for generating new correction information used by the reading means based on the bending information stored in the storage means.

Claims (15)

Printing means for printing a chart in which patterns each including an image object made of a first process color and an image object made of a second process color are arranged at a plurality of positions in the main scanning direction;
Receiving means for receiving, from a user, a plurality of information relating to color misregistration correction between the first process color and the second process color corresponding to each of the plurality of positions based on each pattern arranged in a printed chart; ,
Correction means for performing color misregistration correction between the first process color and the second process color based on the received plurality of information;
An image forming apparatus comprising: The printing means prints the chart by printing a predetermined bitmap,
The predetermined bitmap includes a plurality of regions corresponding to the plurality of positions,
Each region includes a plurality of patterns including an image object composed of the first process color and an image object composed of the second process color,
Each of the plurality of patterns included in one of the plurality of regions has a distance in the sub-scanning direction between the image object composed of the first process color and the image object composed of the second process color. The image forming apparatus according to claim 1, wherein the image forming apparatuses are arranged differently.   The correction means calculates a printing position misalignment characteristic of the first process color in the sub-scanning direction based on the received plurality of information, and the bit of the first process color based on the calculated characteristic. The image forming apparatus according to claim 1, wherein the color misregistration correction is performed by shifting pixels included in the map in a sub-scanning direction.   The correction means calculates a printing position shift characteristic of the second process color in the sub-scanning direction based on the received plurality of information, and the second process color bit based on the calculated characteristic. The image forming apparatus according to claim 3, wherein the color misregistration correction is performed by shifting pixels included in the map in a sub-scanning direction. First storage means for storing a first characteristic of a printing position shift in the sub-scanning direction of the first process color and a second characteristic of a printing position shift in the sub-scanning direction of the second process color;
Second storage means for storing a predetermined bitmap corresponding to the chart;
Have
The correction means includes
Based on the stored first characteristic, the pixels included in the bitmap of the first process color in the stored predetermined bitmap are shifted in the sub-scanning direction,
Based on the stored second characteristic, the pixels included in the second process color bitmap in the stored predetermined bitmap are shifted in the sub-scanning direction,
5. The image forming apparatus according to claim 3, wherein the printing unit prints the chart by performing printing based on the predetermined bitmap in which pixel shift is performed by the correction unit. The first process color is one of four colors of cyan, magenta, yellow, and black,
The image forming apparatus according to claim 1, wherein the second process color is any one of the four colors different from the first process color. .   The image forming apparatus according to claim 1, wherein the plurality of positions in the main scanning direction are three different positions in the main scanning direction. A printing step of printing a chart in which a pattern including an image object composed of a first process color and an image object composed of a second process color is arranged at each of a plurality of positions in the main scanning direction;
A receiving step of receiving, from a user, a plurality of pieces of information regarding color misregistration correction between the first process color and the second process color corresponding to each of the plurality of positions, based on each pattern arranged in a printed chart; ,
A correction step for correcting color misregistration between the first process color and the second process color based on the received plurality of information;
An image forming method comprising: The printing step prints the chart by printing a predetermined bitmap,
The predetermined bitmap includes a plurality of regions corresponding to the plurality of positions,
Each region includes a plurality of patterns including an image object composed of the first process color and an image object composed of the second process color,
Each of the plurality of patterns included in one of the plurality of regions has a distance in the sub-scanning direction between the image object composed of the first process color and the image object composed of the second process color. The image forming method according to claim 8, wherein the image forming methods are arranged differently.   The correction step calculates a printing position shift characteristic of the first process color in the sub-scanning direction based on the received plurality of information, and the bit of the first process color is calculated based on the calculated characteristic. The image forming method according to claim 8, wherein the color misregistration correction is performed by shifting a pixel included in the map in a sub-scanning direction.   The correction step calculates a printing position deviation characteristic of the second process color in the sub-scanning direction based on the received plurality of information, and the second process color bit based on the calculated characteristic. The image forming method according to claim 10, wherein the color misregistration correction is performed by shifting pixels included in a map in a sub-scanning direction. A first storage step of storing a first characteristic of a printing position shift in the sub-scanning direction of the first process color and a second characteristic of a printing position shift in the sub-scanning direction of the second process color;
A second storage step of storing a predetermined bitmap corresponding to the chart;
Have
The correction step includes
Based on the stored first characteristic, the pixels included in the bitmap of the first process color in the stored predetermined bitmap are shifted in the sub-scanning direction,
Based on the stored second characteristic, the pixels included in the second process color bitmap in the stored predetermined bitmap are shifted in the sub-scanning direction,
12. The image forming method according to claim 10, wherein the printing step prints the chart by performing printing based on the predetermined bitmap in which pixel shift is performed by the correction unit. The first process color is one of four colors of cyan, magenta, yellow, and black,
The image forming method according to claim 1, wherein the second process color is any one of the four colors different from the first process color. .   The image forming method according to claim 8, wherein the plurality of positions in the main scanning direction are three different positions in the main scanning direction.   A program that causes a computer to function as each of the means according to claim 1.

Images