Image forming apparatus

Abstract

To obtain an image forming apparatus which can perform correction processing for reducing a white stripe and a black stripe caused by an ink discharge order also in the case of an automatic centering function.SOLUTION: Recording heads 1a to 1d discharge ink corresponding to an image to be printed by a nozzle 11a. A control section 81 determines the nozzle 11a corresponding to the image to be printed according to a position of a print sheet and causes the recording heads 1a to 1d to discharge ink from the nozzle 11a. A correction processing section 83 executes correction processing corresponding to a density failure generated caused by a discharge order of the nozzle 11a for an image after gradation processing. Concretely, the correction processing section 83 executes the correction processing for the density of a target pixel in which the density failure is generated on the basis of the total of density of peripheral pixels positioned by a prescribed distance from the target pixel in the image after the gradation processing.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] In an inkjet image forming apparatus, white or black stripes may appear in a printed image due to the ink ejection order and nozzle ejection defects, and correction processing is performed to reduce the white or black stripes. One image forming apparatus performs correction processing on an image before halftone processing using a correction coefficient corresponding to a droplet interference pattern corresponding to the ink ejection order and ejection defects (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-201121 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a line-type inkjet image forming device with a fixed recording head, when adjusting the ink ejection position corresponding to a print image so that the center of the print sheet coincides with the center of the print image depending on the position of the print sheet in the main scanning direction being transported (in the case of an automatic centering function), the nozzles corresponding to each pixel of the print image are selected after the printing operation (such as transporting the print sheet) has begun, making it difficult for the above-mentioned device to perform correction processing.

[0005] The present invention has been made in consideration of the above problems, and has an object to provide an image forming apparatus that can perform correction processing to reduce white and black streaks caused by the ink ejection order, even in the case of an automatic centering function. [Means for solving the problem]

[0006] The image forming apparatus according to the present invention includes a recording head that ejects ink from nozzles corresponding to an image to be printed, a control unit that determines the nozzles corresponding to the image to be printed according to the position of a print sheet and causes the recording head to eject ink from the nozzles, and a correction processing unit that executes a correction process on the image after gradation processing to address density defects that occur due to the ejection order of the nozzles.The correction processing unit executes the correction process on the density of a pixel of interest at which the density defect occurs in the image after gradation processing based on the sum of the densities of surrounding pixels at a predetermined distance from the pixel of interest. Effect of the Invention

[0007] According to the present invention, an image forming apparatus can be obtained that can perform correction processing to reduce white and black streaks caused by the ink ejection order even in the case of an automatic centering function.

[0008] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a side view illustrating the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing an example of the recording heads 1a, 1b, 1c, and 1d in the image forming apparatus 10 shown in FIG. [Diagram 3] FIG. 3 is a diagram showing an example of the head unit 11 in FIG. [Figure 4] FIG. 4 is a diagram for explaining density defects (black streaks and white streaks) caused by the ink ejection order. [Diagram 5] FIG. 5 is a block diagram showing an electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. [Figure 6] FIG. 6 is a diagram illustrating neighboring pixels of a pixel of interest. [Figure 7] FIG. 7 is a diagram showing an example of the surrounding density group. [Figure 8] FIG. 8 is a diagram for explaining the ejection order pattern. [Figure 9] FIG. 9 is a flowchart illustrating the operation of the image forming apparatus 10 shown in FIGS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] 1 is a side view illustrating the internal mechanical configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus according to this embodiment is a device such as a printer, a copier, a facsimile machine, or a multifunction machine.

[0012] The image forming apparatus 10 shown in Fig. 1 includes a print engine 10a and a sheet conveying unit 10b. The print engine 10a physically forms a page image to be printed on a print sheet (e.g., a print sheet). In this embodiment, the print engine 10a is a line-type inkjet print engine.

[0013] In this embodiment, print engine 10a includes line-type recording heads 1a to 1d corresponding to four ink colors, namely cyan, magenta, yellow, and black.

[0014] Fig. 2 is a plan view showing an example of the recording heads 1a, 1b, 1c, and 1d in the image forming apparatus 10 shown in Fig. 1. For example, as shown in Fig. 2, in this embodiment, each of the recording heads 1a, 1b, 1c, and 1d has a plurality of head portions 11 (three in this embodiment). These head portions 11 are arranged along the main scanning direction and are detachable from the main body of the apparatus. Note that the recording heads 1a, 1b, 1c, and 1d may each have only one head portion 11.

[0015] Fig. 3 is a diagram showing an example of the head unit 11 in Fig. 2. For example, as shown in Fig. 3, the head unit 11 of the recording heads 1a, 1b, 1c, and 1d includes nozzles 11a arranged two-dimensionally, and ejects ink from the nozzles corresponding to an image to be printed.

[0016] The nozzles 11a of each recording head 1a, 1b, 1c, 1d are classified into multiple nozzle rows, and when a certain position in the sub-scanning direction (transport direction) of the print sheet passes the position of a certain nozzle row, ink droplets are ejected from the nozzles 11a (first ejection nozzles) of that nozzle row, and then, when that position of the print sheet passes the position of another nozzle row, ink droplets are ejected from the nozzles 11a (last ejection nozzles) of that nozzle row. In other words, a dot (last ejection dot) formed by ink droplets ejected later is formed adjacent to a dot (first ejection dot) formed by ink droplets ejected earlier.

[0017] FIG. 4 is a diagram for explaining density defects (black streaks and white streaks) caused by the ink ejection order. Due to unevenness in the nozzle spacing, for example, as shown in FIG. 4, ink droplets ejected later may merge with dots (first ejected dots) formed on the print sheet by first ejection. In that case, the ink droplets ejected later are attracted to the first ejected dots, and the positions of the dots (last ejected dots) formed by the later ejection are shifted. This can result in density defects (black streaks and white streaks). When the pixel of interest is ejected later, the above-mentioned merging of droplets causes the dots to shift, resulting in insufficient density (white streaks) for the pixel of interest, and when the pixel of interest is ejected earlier, the above-mentioned merging of droplets causes the dots of adjacent pixels to shift, resulting in excessive density (black streaks) for the pixel of interest.

[0018] Returning to FIG. 1, the sheet conveying unit 10b conveys the print sheet before printing to the print engine 10a along a predetermined conveying path, and conveys the print sheet after printing from the print engine 10a to a predetermined discharge destination (such as a discharge tray 10c).

[0019] The sheet conveying section 10b includes a main sheet conveying section 10b1 and a circulating sheet conveying section 10b2. In double-sided printing, the main sheet conveying section 10b1 conveys print sheets used for printing a page image on the first side to the print engine 10a, and the circulating sheet conveying section 10b2 conveys print sheets from the rear stage to the front stage of the print engine 10a while retaining a predetermined number of print sheets.

[0020] In this embodiment, the main sheet transport section 10b1 includes a circular transport belt 2 arranged opposite the print engine 10a for transporting the print sheet, a drive roller 3 and a driven roller 4 on which the transport belt 2 is suspended, an adhesion roller 5 that nips the print sheet together with the transport belt 2, and a pair of discharge rollers 6, 6a.

[0021] A driving roller 3 and a driven roller 4 rotate the conveyor belt 2. Then, the suction roller 5 nips the print sheet conveyed from paper feed cassettes 20-1 and 20-2 (described later), and the nipped print sheet is conveyed by the conveyor belt 2 to the printing positions of the recording heads 1a to 1d in order, and the recording heads 1a to 1d print images of each color. Then, after color printing is completed, the print sheet is discharged to a discharge tray 10c or the like by a pair of discharge rollers 6 and 6a.

[0022] Furthermore, the main sheet transport section 10b1 includes a plurality of paper feed cassettes 20-1, 20-2. The paper feed cassettes 20-1, 20-2 store print sheets SH1, SH2, and the lift plates 21, 24 push the print sheets SH1, SH2 upward to abut against the pickup rollers 22, 25. The print sheets SH1, SH2 placed on the paper feed cassettes 20-1, 20-2 are picked up one by one from above by the pickup rollers 22, 25 to the paper feed rollers 23, 26. The paper feed rollers 23, 26 are rollers that transport the print sheets SH1, SH2, which are fed from the paper feed cassettes 20-1, 20-2 by the pickup rollers 22, 25, one by one onto the transport path. The transport roller 27 is a transport roller on the transport path common to the print sheets SH1, SH2 transported from the paper feed cassettes 20-1, 20-2.

[0023] The circulating sheet transport unit 10b2 returns the print sheet from a predetermined position downstream of the print engine 10a to a predetermined position upstream of the print engine 10a (here, a predetermined position upstream of a line sensor 31 described later) during double-sided printing. The circulating sheet transport unit 10b2 includes a transport roller 41 and a switchback transport path 41a that reverses the traveling direction of the print sheet to switch the side of the print sheet facing the print engine 10a from the first side to the second side.

[0024] The image forming apparatus 10 further includes a line sensor 31 and a sheet detection sensor 32. The line sensor 31 is an optical sensor that is arranged along a direction perpendicular to the conveying direction of the print sheet and detects the positions of both end edges (both side edges) of the print sheet. For example, the line sensor 31 is a CIS (Contact Image Sensor). In this embodiment, the line sensor 31 is arranged between the registration roller 28 and the print engine 10a. The sheet detection sensor 32 is an optical sensor that detects that the leading ends of the print sheets SH1 and SH2 have passed a predetermined position on the conveying path. The line sensor 31 detects the positions of both end edges of the print sheets when the leading ends of the print sheets SH1 and SH2 are detected by the sheet detection sensor 32.

[0025] For example, as shown in FIG. 1, the print engine 10a is disposed above or below the transport path of the print sheet (here, the upper side), the line sensor 31 is disposed above or below the transport path of the print sheet (here, the lower side), and the circulating sheet transport section 10b2 transports the print sheet by switching back from the downstream side of the print engine 10a to the upstream side of the line sensor 31.

[0026] Fig. 5 is a block diagram showing the electrical configuration of image forming apparatus 10 according to the embodiment of the present invention. As shown in Fig. 5, image forming apparatus 10 includes image output unit 71 having the mechanical configuration as shown in Figs. 1 to 3, as well as operation panel 72, storage device 73, image reader 74, and controller 75.

[0027] The operation panel 72 is arranged on the surface of the housing of the image forming apparatus 10 and includes a display device 72a such as an LCD display, and an input device 72b such as hard keys or a touch panel. The display device 72a displays various messages to the user, and the input device 72b accepts user operations.

[0028] The storage device 73 is a non-volatile storage device (such as a flash memory or a hard disk drive) that stores data, programs, and the like required for controlling the image forming apparatus 10.

[0029] The image reading device 74 includes a platen glass and an automatic document feeder, and optically reads the image of a document placed on the platen glass or a document transported by the automatic document feeder, and generates image data of that image.

[0030] The controller 75 includes a computer that executes software processing according to a program, and an ASIC (Application Specific Integrated Circuit) that executes predetermined hardware processing, and operates as various processing units. The computer includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and operates as various processing units (together with the ASIC as necessary) by loading a program stored in the ROM, storage device 73, etc., into the RAM and executing it on the CPU. Here, the controller 75 operates as a control unit 81, an image processing unit 82, and a correction processing unit 83.

[0031] The control unit 81 controls the image output unit 71 (print engine 10a, sheet conveying unit 10b, etc.) to execute a print job requested by a user. In this embodiment, the control unit 81 causes the image processing unit 82 to execute predetermined image processing, and controls the print engine 10a (head unit 11) to eject ink to form a print image on a print sheet. The image processing unit 82 executes predetermined image processing such as RIP (Raster Image Processing), color conversion, and gradation processing on image data of an image to be printed on a print sheet.

[0032] Furthermore, in this embodiment, the control unit 81 has an automatic centering function that (a) identifies the center position of the print sheet as the actual sheet center position based on the positions of both end edges of the print sheet detected by the line sensor 31, and (b) adjusts the center position of the image to be printed based on the actual sheet center position, and executes the automatic centering function as hardware processing.

[0033] Specifically, in the automatic centering function, the control unit 81 changes the drawing position of the image to be printed along the main scanning direction by the difference between the reference center position of the print engine 10a and the actual sheet center position. In this embodiment, since the nozzles 11a in the recording heads 1a to 1d do not move, the nozzles corresponding to each pixel in the image to be printed are changed according to the drawing position of the image to be printed.

[0034] In this way, the control unit 81 determines the nozzles 11a (nozzles 11a corresponding to each pixel) corresponding to the image to be printed according to the position on the print sheet, and causes the recording heads 1a to 1d to eject ink from the nozzles 11a.

[0035] Furthermore, the correction processing unit 83 executes a correction process for the image after the gradation process to deal with density defects that occur due to the ejection order of the nozzles 11a.

[0036] In the correction process, during the time from when the print sheet position is specified to when the ink is discharged, the correction processing unit 83 (a) specifies a pixel corresponding to the nozzle 11a where density defects occur due to the coalescence of the above-mentioned droplets, that is, a pixel (a pixel of interest) that is to be subjected to the correction process in the image to be printed, and (b) performs the correction process on that pixel. The nozzle 11a where density defects occur due to the coalescence of the above-mentioned droplets is specified in advance by an existing method such as an experiment or an inspection using a test pattern, or is specified in advance based on the configuration of the recording heads 1a to 1d, and the setting data 73a indicating that nozzle 11a is stored in advance in the storage device 73.

[0037] Specifically, the correction processing unit 83 performs a correction process on the density of a pixel of interest in an image after gradation processing, where the above-mentioned density defect occurs, based on the sum of the densities (here, pixel values ​​indicating density) of surrounding pixels within a predetermined distance from the pixel of interest.

[0038] Fig. 6 is a diagram for explaining peripheral pixels of a pixel of interest. Fig. 7 is a diagram showing an example of peripheral density groups. In this embodiment, (a) the density sum for peripheral pixels (inner peripheral pixels in Fig. 6) whose predetermined distance is one pixel is classified into a plurality of density classes using a plurality of thresholds TH1 to TH4, (b) the density sum for peripheral pixels (outer peripheral pixels in Fig. 6) whose predetermined distance is two pixels is classified into a plurality of density classes using a plurality of thresholds TH5 to TH7, (c) as shown in Fig. 7, for example, a plurality of peripheral density groups are set by combining the density classes of the inner peripheral pixels and the density classes of the outer peripheral pixels, and (d) a correction amount is set for each of the plurality of peripheral density groups.

[0039] In this embodiment, the correction processing unit 83 (a) identifies a surrounding density group (here, any one of groups #1 to #5 in FIG. 7) to which the combination of the density sum of the inner surrounding pixels and the density sum of the outer surrounding pixels belongs for the pixel of interest, (b) identifies a correction amount corresponding to the identified surrounding density group, and (c) performs a correction process with the identified correction amount. Here, the pixel value of the pixel of interest is increased or decreased by the correction amount.

[0040] This correction amount is set to zero when the pixel of interest is an isolated dot, and increases as the sum of the densities of the inner surrounding pixels and the sum of the densities of the outer surrounding pixels increase, and is set to decrease when the sum of the densities of the inner surrounding pixels and the sum of the densities of the outer surrounding pixels exceed a predetermined value.

[0041] Furthermore, if the pixel of interest is ejected before the adjacent pixels in the ejection order, the correction processing unit 83 executes a correction process to reduce the density of the pixel of interest (because the pixel of interest has an excessive density as described above), and if the pixel of interest is ejected after the adjacent pixels in the ejection order, the correction processing unit 83 executes a correction process to increase the density of the pixel of interest (because the pixel of interest has an insufficient density as described above). In other words, the above-mentioned correction amount is set so that the correction process is executed in this manner. Specifically, in the case of first ejection, the correction amount is set to a negative value, and in the case of last ejection, the correction amount is set to a positive value, and the density of the pixel of interest is corrected to a value obtained by adding the correction amount to the density of the pixel of interest. By increasing or decreasing the density of the pixel of interest in this way, the amount of ink droplets ejected increases or decreases, and the size of the dots formed by the droplets landing increases or decreases.

[0042] Furthermore, if the total density of the inner surrounding pixels is zero and the total density of the outer surrounding pixels is zero, the correction processing unit 83 determines that the pixel of interest is an isolated dot and does not perform correction processing.

[0043] Furthermore, if the pixel of interest is discharged after the adjacent pixels in the discharge order, the correction processing unit 83 does not perform correction processing if the total density of the inner peripheral pixels is zero and the total density of the outer peripheral pixels is equal to or less than the predetermined threshold value. On the other hand, if the pixel of interest is discharged before the adjacent pixels in the discharge order, the correction processing unit 83 performs correction processing if the total density of the inner peripheral pixels is zero and the total density of the outer peripheral pixels exceeds zero and is equal to or less than the above-mentioned predetermined threshold value.

[0044] Moreover, the above-mentioned correction amount is set according to the discharge order pattern. FIG. 8 is a diagram for explaining the discharge order pattern. As shown in FIG. 8, patterns #1 to #4 are set as the discharge order pattern. In pattern #1, the pixel of interest is later discharged (pixel drawn by later discharge nozzle), and both adjacent pixels of the pixel of interest (adjacent pixels in the main scanning direction) are earlier discharged (pixel drawn by earlier discharge nozzle). In pattern #2, the pixel of interest is earlier discharged, and both adjacent pixels of the pixel of interest are later discharged. In pattern #3, the pixel of interest is earlier discharged, one of the adjacent pixels of the pixel of interest is later discharged and the other is earlier discharged. In pattern #4, the pixel of interest is later discharged, one of the adjacent pixels of the pixel of interest is later discharged and the other is earlier discharged.

[0045] For example, when the pixel value of each pixel of the image to be printed is quantized to four gradation levels of 0, 1, 2, and 3 by gradation processing, the range of the total density of the inner peripheral pixels (8 pixels) is 0 to 24, and the range of the total density of the outer peripheral pixels (16 pixels) is 0 to 48. In this case, the thresholds TH1, TH2, TH3, TH4, TH5, TH6, and TH7 are set to, for example, 1, 16, 32, 48, 1, 8, and 15. In this case, for pattern #1, for example, the correction amount of groups #1 and #2 in FIG. 7 is set to 0, the correction amount of group #3 is set to -1, the correction amount of group #4 is set to -2, and the correction amount of group #5 is set to -1. Also, in this case, for pattern #2, for example, the correction amount of group #1 in FIG. 7 is set to 0, the correction amount of groups #2 and #3 is set to 1, and the correction amount of groups #4 and #5 is set to 0. In this case, for pattern #3, for example, the correction amount of group #1 in Fig. 7 is set to 0, the correction amount of groups #2, #3, and #4 is set to 1, and the correction amount of group #5 is set to 0. In this case, for pattern #4, for example, the correction amount of groups #1 and #2 in Fig. 7 is set to 0, and the correction amount of groups #3, #4, and #5 is set to -1.

[0046] Such correction amounts for each surrounding density group are associated with the surrounding density group as data and stored in advance in the storage device 73, and are referred to when deriving the correction amount for the pixel of interest.

[0047] Next, a description will be given of the operation of the image forming apparatus 10. Fig. 9 is a flow chart for explaining the operation of the image forming apparatus 10 shown in Figs.

[0048] When the control unit 81 receives a print request, the image processing unit 82 performs image processing such as gradation processing on the image specified by the print request to obtain image data of the image to be printed (image after gradation processing), and identifies the image to be printed (image after gradation processing) (step S1).

[0049] Next, the correction processing unit 83 reads out the setting data 73a and identifies the nozzle 11a to be corrected (step S2).

[0050] Then, the control unit 81 starts transporting the print sheet in the image output unit 71 (step S3), and when the position of the print sheet is detected by the line sensor 31 (step S4), it derives the position correction amount of the image to be printed (step S5) and shifts the image to be printed in the main scanning direction by the position correction amount.

[0051] The correction processing unit 83 identifies the nozzles 11a corresponding to each pixel of the image to be printed that has been shifted by the position correction amount, and identifies the pixel (target pixel) corresponding to the nozzle 11a to be corrected (step S6).

[0052] Furthermore, the correction processing unit 83 identifies the discharge order pattern for the pixel of interest (step S7), and derives the density sum of the inner surrounding pixels for the pixel of interest and the density sum of the outer surrounding pixels for the pixel of interest in the image (step S8).

[0053] Then, the correction processing unit 83 identifies a correction amount corresponding to the ejection sequence pattern, the sum of the densities of the inner surrounding pixels, and the sum of the densities of the outer surrounding pixels for the pixel of interest (step S9), and performs density correction of the pixel of interest by increasing or decreasing the density (pixel value) of the pixel of interest by the correction amount (step S10).

[0054] Based on the image in which the density of each pixel of interest has been corrected in this manner, the control unit 81 ejects ink droplets from the corresponding nozzle 11a in a droplet volume corresponding to the density (pixel value) of each pixel of the image, thereby forming an image on the print sheet (step S11).

[0055] As described above, according to the embodiment, the recording heads 1a to 1d eject ink corresponding to an image to be printed from the nozzles 11a. The control unit 81 determines the nozzles 11a corresponding to the image to be printed according to the position of the print sheet, and causes the recording heads 1a to 1d to eject ink from the nozzles 11a. The correction processing unit 83 executes a correction process for the image after the gradation process to deal with density defects caused by the ejection order of the nozzles 11a. Specifically, the correction processing unit 83 executes a correction process for the density of a pixel of interest where density defects occur in the image after the gradation process, based on the sum of the densities of surrounding pixels at a predetermined distance from the pixel of interest.

[0056] As a result, even in the case of the automatic centering function, a correction process is performed to reduce white and black streaks caused by the ink ejection order. In addition, since the correction amount is determined according to the peripheral density of the target pixel in the correction process, the density correction of the target pixel is performed appropriately.

[0057] It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. In other words, such changes and modifications are intended to be included within the scope of the claims.

[0058] For example, in the above embodiment, the image is processed to have four gradations, but it may have eight or sixteen gradations. [Industrial Applicability]

[0059] The present invention is applicable to, for example, an inkjet type image forming apparatus. [Explanation of symbols]

[0060] 1a~1d Recording head 10 Image forming device 11a Nozzle 81 Control Unit 83 Correction processing section

Claims

1. a recording head for ejecting ink from nozzles corresponding to an image to be printed; a control unit that determines nozzles corresponding to an image to be printed according to a position of a print sheet and causes the recording head to eject ink from the nozzles; a correction processing unit that executes a correction process for the image after the gradation process, the correction process corresponding to a density defect that occurs due to an ejection order of the nozzles, the correction processing unit executes the correction process on the basis of a sum of densities of surrounding pixels at a predetermined distance from a pixel of interest where the density defect occurs, in the image after the gradation process; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the correction processing unit does not perform the correction processing when the sum for the surrounding pixels where the specified distance is one pixel is zero, and when the sum for the surrounding pixels where the specified distance is two pixels is zero.

3. The image forming apparatus according to claim 1, characterized in that, when the pixel of interest is discharged after the adjacent pixels in the discharge order, the correction processing unit does not perform the correction processing when the sum for the surrounding pixels whose specified distance is one pixel is zero and the sum for the surrounding pixels whose specified distance is two pixels is less than a specified threshold, and when the pixel of interest is discharged before the adjacent pixels in the discharge order, the correction processing unit performs the correction processing when the sum for the surrounding pixels whose specified distance is one pixel is zero and the sum for the surrounding pixels whose specified distance is two pixels exceeds zero and is less than the specified threshold.

4. The image forming apparatus according to claim 1, characterized in that the correction processing unit performs the correction processing so as to reduce the density of the pixel of interest when the pixel of interest is ejected before the adjacent pixels in the ejection order, and performs the correction processing so as to increase the density of the pixel of interest when the pixel of interest is ejected after the adjacent pixels in the ejection order.

5. (a) classifying the sum for the surrounding pixels whose predetermined distance is one pixel into a plurality of density classes using a plurality of threshold values; (b) classifying the sum for the surrounding pixels whose predetermined distance is two pixels into a plurality of density classes using a plurality of threshold values; (c) setting a plurality of surrounding density groups by combining the density classes of the surrounding pixels whose predetermined distance is one pixel with the density classes of the surrounding pixels whose predetermined distance is two pixels; (d) setting a correction amount for each of the plurality of surrounding density groups; the correction processing unit (a) identifies, for the pixel of interest, a surrounding density group to which a combination of the sum for the surrounding pixels whose predetermined distance is one pixel and the sum for the surrounding pixels whose predetermined distance is two pixels belongs, (b) identifies a correction amount corresponding to the identified surrounding density group, and (c) performs the correction process using the identified correction amount.

2. The image forming apparatus according to claim 1,

Images