Image forming device

Abstract

To provide an image forming device that performs image formation with good gradation characteristics while suppressing cost rise / increase.SOLUTION: A drive waveform selecting part 81a selects a drive waveform for an attention pixel in an image to be printed, out of drive waveforms corresponding to a plurality of predetermined droplet quantities. The plurality of droplet quantities described above include first droplet quantities for a halftone area and second droplet quantities for correction corresponding to a poor discharge poor nozzle, but do not include droplet quantities for expressing a solid area of the maximum density, with single droplet quantities, where the second droplet quantities are more than the maximum droplet quantities of the first droplet quantities. When the attention pixel belongs to the solid area of the maximum density in the image to be printed, the drive waveform selecting part 81a selects, as the drive waveform for the attention pixel, a drive waveform corresponding to the maximum droplet quantities or a drive waveform corresponding to the second droplet quantities so that the maximum droplet quantities and the second droplet quantities appear in a predetermined pattern.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Inkjet image forming devices control the recording head to eject ink droplets from the recording head to form dots on a print sheet, and drive the recording head with a drive signal having a drive waveform that corresponds to the dot diameter (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-280495 A Summary of the Invention [Problem to be solved by the invention]

[0004] Typically, when forming a solid portion of maximum density, the recording head is driven by a drive signal having a drive waveform corresponding to a large dot diameter, and when forming a halftone portion, the recording head is driven by a drive signal having a drive waveform corresponding to a dot diameter smaller than the large dot diameter.

[0005] Furthermore, if it were possible to form dots with a larger dot diameter in order to form halftone portions, good gradation characteristics would be obtained and the minimum dot diameter could be set small, reducing the graininess.

[0006] However, in order to drive the print head with a drive signal having a drive waveform corresponding to many dot diameters, the circuit scale becomes large and a large storage area is required for the data representing those drive waveforms, which increases the cost of the device.

[0007] The present invention has been made in view of the above problems, and has an object to provide an image forming apparatus which forms images with good gradation characteristics while suppressing increases in cost. [Means for solving the problem]

[0008] The image forming apparatus according to the present invention includes a recording head that ejects ink corresponding to an image to be printed from an array of nozzles, a drive waveform selection unit that selects a drive waveform for a pixel of interest in the image from among drive waveforms corresponding to a plurality of predetermined droplet amounts, and a control unit that supplies a drive signal of the selected drive waveform to the recording head to cause the recording head to eject ink. Here, the plurality of droplet amounts include one or more droplet amounts for a halftone region and a second droplet amount for correction corresponding to a nozzle with a discharge defect, and does not include a droplet amount for expressing a solid area of ​​maximum density with a single droplet amount, and the second droplet amount is greater than a maximum droplet amount of the one or more first droplet amounts. If the pixel of interest belongs to a solid area of ​​maximum density in the image, the drive waveform selection unit performs a conversion process, and in the conversion process, selects a drive waveform corresponding to the maximum droplet amount of the first droplet amount or a drive waveform corresponding to the second droplet amount as a drive waveform for the pixel of interest so that the maximum droplet amount of the first droplet amount and the second droplet amount appear in a predetermined pattern. Effect of the Invention

[0009] According to the present invention, it is possible to obtain an image forming apparatus which forms images with good gradation characteristics while suppressing increases in cost.

[0010] 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]

[0011] [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 block diagram showing an electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining dots formed by the driving waveform after the conversion process. [Diagram 5] FIG. 5 is a diagram for explaining an example of a filter used in the spatial filtering process of the drive waveform selection section 81a. [Figure 6] FIG. 6 is a diagram showing an example of a comparison between a case where a low gradation portion judgment is performed and a case where a low gradation portion judgment is not performed. [Figure 7] FIG. 7 is a flowchart illustrating the operation of the image forming apparatus 10 shown in FIGS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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 units 11 (three in this embodiment). The head units 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 unit 11. The head units 11 of the recording heads 1a, 1b, 1c, and 1d each have nozzles arranged two-dimensionally corresponding to the ejection positions arranged in the main scanning direction, and eject ink corresponding to the image to be printed from the nozzles.

[0017] The sheet transport section 10b transports the print sheet before printing to the print engine 10a along a predetermined transport path, and transports the print sheet after printing from the print engine 10a to a predetermined discharge destination (such as a discharge tray 10c).

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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 above), the line sensor 31 is disposed above or below the transport path of the print sheet (here, the below), 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.

[0025] Fig. 3 is a block diagram showing the electrical configuration of the image forming apparatus 10 according to the embodiment of the present invention. As shown in Fig. 3, the image forming apparatus 10 includes an image output unit 71 having the mechanical configuration as shown in Fig. 1 and Fig. 2, as well as an operation panel 72, a storage device 73, an image reader 74, and a controller 75.

[0026] 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.

[0027] 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.

[0028] 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 conveyed by the automatic document feeder, and generates image data of that image.

[0029] 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), ROM (Read Only Memory), RAM (Random Access Memory), and operates as various processing units (together with the ASIC as necessary) by loading programs stored in the ROM, storage device 73, etc. into the RAM and executing them on the CPU. Here, the controller 75 operates as a control unit 81, an image processing unit 82, a defective nozzle detection unit 83, and a correction processing unit 84.

[0030] 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 (halftoning processing) on ​​image data of an image to be printed on a print sheet.

[0031] In this embodiment, the control unit 81 has an automatic centering function that (a) specifies the center position of the print sheet as the actual sheet center position based on the positions of both edge portions 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. 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, the nozzles in the recording heads 1a to 1d do not move, so 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.

[0032] In this way, the control unit 81 determines the nozzles corresponding to the image to be printed (the nozzles corresponding to each pixel of the image) (here, according to the position on the print sheet), and causes the recording heads 1a to 1d to eject ink from the nozzles.

[0033] The defective nozzle detection unit 83, for example, (a) prints a test pattern on a print sheet using the recording heads 1a to 1d, and (b) detects defective nozzles (non-ejecting nozzles in this case) based on the density distribution of the read image of the test pattern. The defective nozzle detection unit 83 also stores defective nozzle data (nozzle number, etc.) indicating the detected defective nozzles in the storage device 73. The test pattern is an existing one, and is, for example, a band-shaped image of a single density, or an image including thin lines corresponding to each nozzle.

[0034] The correction processing unit 84 executes a correction process for the image to be printed that corresponds to the nozzle to be corrected. In this correction process, for example, the image data (pixel value) of the pixel corresponding to the nozzle with the ejection failure is corrected so that ink is not ejected, and the image data (pixel value) of the pixel corresponding to the nozzle adjacent to the ejection failure nozzle is corrected so that the density of the pixel is increased.

[0035] As described above, in the image forming apparatus 10, correction processing is performed on the correction target nozzles adjacent to the ejection failure nozzles, in which the ink ejection droplet amount is increased to form dots with the droplet amount LL.

[0036] Further, the control unit 81 includes a drive waveform selection unit 81a, and the drive waveform selection unit 81a selects a drive waveform for a target pixel in the image to be printed from drive waveforms corresponding to a plurality of predetermined droplet amounts.

[0037] Here, the plurality of droplet amounts include one or more first droplet amounts (here, two, the droplet amount S and the droplet amount M (S < M)) for the halftone region, and a second droplet amount (the droplet amount LL) for correction corresponding to the ejection failure nozzles, and do not include a droplet amount (the droplet amount L, which is intermediate between the droplet amount M and the droplet amount LL) for expressing the solid region of the maximum density with a single droplet amount. Also, the second droplet amount (the droplet amount LL) is larger than the maximum droplet amount (the droplet amount M) among the one or more first droplet amounts.

[0038] Note that when the nozzle corresponding to the target pixel is a correction target nozzle adjacent to the non-ejecting ejection failure nozzle, the drive waveform selection unit 81a selects the drive waveform corresponding to the second droplet amount (the droplet amount LL) as the drive waveform for the target pixel.

[0039] Then, the control unit 81 supplies the drive signal of the selected drive waveform to the recording heads 1a to 1d to eject ink from the recording heads 1a to 1d (the parts that drive the nozzles corresponding to the target image). For example, data indicating each drive waveform is stored in the storage device 73 or the like, and the control unit 81 reads out the data of the selected drive waveform from the storage device 73 or the like and generates a drive signal based on the data.

[0040] Furthermore, when the pixel of interest belongs to a solid area of ​​maximum density in the image to be printed, the drive waveform selection unit 81a performs a conversion process, and selects, as the drive waveform for the pixel of interest, a drive waveform corresponding to the maximum first droplet amount (droplet amount M) or a drive waveform corresponding to the second droplet amount (droplet amount LL) so that the maximum first droplet amount (droplet amount M) and the second droplet amount (droplet amount LL) appear in a predetermined pattern in the conversion process.

[0041] That is, for maximum density solid areas, instead of a single droplet volume M, a predetermined pattern of different droplet volumes M, LL is used.

[0042] Fig. 4 is a diagram illustrating dots formed by the driving waveform after conversion processing. In this embodiment, for example, as shown in Fig. 4, the driving waveform selection unit 81a selects a driving waveform corresponding to the droplet amount M or a driving waveform corresponding to the droplet amount LL as the driving waveform for the pixel of interest so that the droplet amount M and the droplet amount LL appear alternately for each dot.

[0043] By doing so, even if a nozzle corresponding to a pixel of interest is distorted in ejection as shown in FIG. 4, for example, density loss is less likely to occur.

[0044] The above-mentioned predetermined pattern and droplet amounts M and LL are set so that the corresponding area on the print sheet becomes a solid area of ​​maximum density. Here, if the amount of a single droplet capable of forming a solid area of ​​maximum density is L, the droplet amounts M and LL are set to satisfy the formula L = (M + LL) / 2.

[0045] Here, the drive waveform selection unit 81a determines whether or not the pixel of interest belongs to a solid area of ​​maximum density in the image to be printed by spatial filtering.

[0046] 5 is a diagram for explaining an example of a filter used in the spatial filtering process of the driving waveform selection unit 81a. Here, an image is subjected to ternary processing, and each pixel in the image has one of three pixel values.

[0047] In the case of a filter of Pattern #1, if the pixel of interest has a pixel value corresponding to droplet volume M and the eight pixels surrounding the pixel of interest have pixel values ​​corresponding to droplet volume M, the pixel of interest is determined to belong to a solid area of ​​maximum density and is rendered with a dot of droplet volume M or droplet volume LL.

[0048] In the case of a filter of Pattern #2, if the pixel of interest has a pixel value corresponding to droplet volume M, and the four surrounding pixels above, below, left, right, or diagonally around the pixel of interest also have pixel values ​​corresponding to droplet volume M, then the pixel of interest is determined to belong to a solid area of ​​maximum density and is rendered with a dot of droplet volume M or droplet volume LL.

[0049] In the case of a filter of pattern #3, when the pixel of interest has a pixel value corresponding to droplet volume M, if the eight surrounding pixels have pixel values ​​corresponding to droplet volume S or droplet volume M, the pixel of interest is determined to belong to a solid area of ​​maximum density and is rendered with a dot of droplet volume M or droplet volume LL.

[0050] For example, the filter used for spatial filtering processing by the drive waveform selection unit 81a may be a filter of pattern #1 or a filter of pattern #2, and further, if necessary, a filter of pattern #3 may be used in addition to the filter.

[0051] Furthermore, in this embodiment, when the pixel of interest belongs to the outline of the solid area, the drive waveform selection unit 81a does not perform conversion processing, and selects the drive waveform corresponding to the droplet volume M as the drive waveform for the pixel of interest. That is, in the case of the above-mentioned filter patterns #1 and #2, when the pixel of interest belongs to the outline, the above-mentioned surrounding pixels are missing, and therefore it is determined that the pixel of interest does not belong to the solid area of ​​maximum density.

[0052] Furthermore, when the pixel of interest is present within a specified low-tone area in the image to be printed, the drive waveform selection unit 81a does not perform a conversion process, but identifies the droplet amount (droplet amount S or droplet amount M) corresponding to the pixel value of the pixel of interest, and selects the drive waveform corresponding to that droplet amount as the drive waveform for the pixel of interest.

[0053] For example, the driving waveform selection unit 81a applies a filter of (2n+1)×(2n+1) pixels (n is an integer) to the pixel of interest, calculates the sum of products of the filter coefficients and the pixel values ​​of corresponding pixels including the pixel of interest, and compares the sum of products with a predetermined threshold to determine whether the pixel of interest is in a low gradation area. Here, the filter coefficients are set to differ depending on the pixel position of the filter and also depending on the driving waveform (droplet volume). If the sum of products is less than the predetermined threshold, the driving waveform selection unit 81a prohibits the conversion process, and if not, permits the conversion process.

[0054] Fig. 6 is a diagram showing an example of a comparison between a case where low gradation part judgment is performed and a case where low gradation part judgment is not performed. For example, as shown in Fig. 6, when low gradation part judgment is performed in this manner, if it is determined that the target pixel exists in the low gradation part, the target pixel is excluded from the target of conversion processing, so that the image quality becomes good.

[0055] Next, a description will be given of the operation of the image forming apparatus 10. Fig. 7 is a flow chart for explaining the operation of the image forming apparatus 10 shown in Figs.

[0056] 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, and the image output unit 71 transports a print sheet and prints the image to be printed on the print sheet based on the image data.

[0057] At this time, the drive waveform selection unit 81a selects, for each pixel of an image (an image to be printed) after gradation processing (for example, ternary processing), a drive waveform corresponding to the pixel value of that pixel, as follows.

[0058] The drive waveform selection unit 81a selects an unprocessed pixel in the gradation-processed image as a pixel of interest (step S1), and determines whether the pixel of interest belongs to a low gradation part as described above (step S2).

[0059] If it is determined that the pixel of interest does not belong to the low gradation area, the drive waveform selection unit 81a determines whether the conversion condition is met for the pixel of interest (i.e., whether the pixel of interest belongs to the maximum density solid area in the image to be printed) (step S3).

[0060] If it is determined that the conversion condition is met, the drive waveform selection unit 81a selects a drive waveform corresponding to the droplet amount M or a drive waveform corresponding to the droplet amount LL according to the pixel position of the pixel of interest (step S4). For example, if the pixel position of the pixel of interest is (x, y), then if x+y is an even number, then the drive waveform corresponding to the droplet amount LL is selected, and if x+y is an odd number, then the drive waveform corresponding to the droplet amount M is selected. As a result, a solid area of ​​maximum density is drawn with the droplet amounts M and LL.

[0061] On the other hand, if it is determined in step S2 that the pixel of interest belongs to the low gradation part, or if it is determined in step S3 that the conversion condition is not satisfied, the drive waveform selection unit 81a selects a drive waveform with a droplet amount according to the pixel value of the pixel of interest (step S5). At this time, in the case of ternary processing, the pixel value of the pixel of interest is classified into no dot, droplet amount S, and droplet amount M by two thresholds, and the drive waveform selection unit 81a selects a drive waveform according to the classification.

[0062] Then, the drive waveform selection unit 81a determines whether the above-mentioned processing has been performed on all pixels of the image after gradation processing (step S6), and if there are unprocessed pixels, returns to step S1, selects a pixel of interest from the unprocessed pixels, and similarly performs the processing from step S2 onwards.

[0063] In this manner, a drive waveform for each pixel is selected, and the control unit 81 supplies a drive signal of the drive waveform selected for each pixel to the recording heads 1a to 1d to cause them to eject ink, thereby forming dots on the print sheet with the corresponding dot diameter.

[0064] As described above, according to the above embodiment, the recording heads 1a to 1d eject ink corresponding to an image to be printed from the arranged nozzles. The drive waveform selection unit 81a selects a drive waveform for a pixel of interest in the image to be printed from drive waveforms corresponding to a predetermined number of droplet amounts. The control unit 81 supplies a drive signal of the selected drive waveform to the recording heads 1a to 1d to cause the recording heads 1a to 1d to eject ink. Here, the above-mentioned multiple droplet amounts include one or more first droplet amounts (here, droplet amounts S and M) for a halftone region and a second droplet amount (here, droplet amount LL) for correction corresponding to a nozzle with a discharge defect, but do not include a droplet amount for a solid region of maximum density, and the second droplet amount (droplet amount LL) is greater than the maximum droplet amount (here, droplet amount M) of the one or more first droplet amounts. Then, when the pixel of interest belongs to a solid area of ​​maximum density in the image to be printed, the drive waveform selection unit 81a performs a conversion process, and selects, as the drive waveform for the pixel of interest, a drive waveform corresponding to the maximum first droplet amount (droplet amount M) or a drive waveform corresponding to the second droplet amount (droplet amount LL) so that the maximum first droplet amount (droplet amount M) and the second droplet amount (droplet amount LL) appear in a predetermined pattern in the conversion process.

[0065] As a result, the maximum density solid area is not drawn with a single droplet amount but with droplet amount M and a correction processing droplet amount LL, so the droplet amounts S and M are set to be relatively small, suppressing graininess and improving gradation characteristics. Also, since there is no drive waveform data or circuit for drawing the maximum density solid area with a single droplet amount, cost increases are suppressed. Therefore, an image forming device that forms images with good gradation characteristics while suppressing cost increases is obtained.

[0066] 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.

[0067] For example, in the above embodiment, the above-mentioned low gradation part judgment may not be performed if it is not necessary. [Industrial Applicability]

[0068] The present invention is applicable to, for example, an inkjet type image forming apparatus. [Explanation of symbols]

[0069] 1a~1d Recording head 10 Image forming device 81 Control Unit 81a Drive waveform selection section 82 Image Processing Section

Claims

1. a print head that ejects ink corresponding to an image to be printed from an array of nozzles; a drive waveform selection unit that selects a drive waveform for a pixel of interest in the image from drive waveforms corresponding to a plurality of predetermined droplet amounts; a control unit that supplies a drive signal of the selected drive waveform to the print head to cause the print head to eject ink, the plurality of droplet amounts include one or more first droplet amounts for a halftone region and a second droplet amount for correction corresponding to a nozzle with a discharge defect, and do not include a droplet amount for expressing a maximum density solid region with a single droplet amount; the second droplet volume is greater than a maximum droplet volume of the one or more first droplet volumes; the drive waveform selection unit performs a conversion process when the pixel of interest belongs to a solid area of ​​maximum density in the image, and selects, in the conversion process, a drive waveform corresponding to the maximum droplet amount of the first droplet amount or a drive waveform corresponding to the second droplet amount as a drive waveform for the pixel of interest, so that the maximum droplet amount of the first droplet amount and the second droplet amount appear in a predetermined pattern; An image forming apparatus comprising:

2. The image forming apparatus according to claim 1, characterized in that, when the pixel of interest belongs to a solid area of ​​maximum density in the image, the drive waveform selection unit selects, as the drive waveform for the pixel of interest, a drive waveform corresponding to the maximum droplet amount of the first droplet amount or a drive waveform corresponding to the second droplet amount, so that the maximum droplet amount of the first droplet amount and the second droplet amount appear alternately for each dot.

3. 3. The image forming apparatus according to claim 2, wherein when the pixel of interest belongs to the outline portion of the solid area, the drive waveform selection unit does not perform the conversion process, and selects a drive waveform corresponding to the maximum droplet volume of the first droplet volume as the drive waveform for the pixel of interest.

4. The image forming apparatus according to claim 1, characterized in that, when the pixel of interest is present in a predetermined low-tone area in the image, the drive waveform selection unit does not perform the conversion process, and selects a drive waveform for the pixel of interest that corresponds to a droplet amount for the pixel value of the pixel of interest.

5. An image forming apparatus as claimed in any one of claims 1 to 4, characterized in that when the nozzle corresponding to the target pixel is a nozzle to be corrected adjacent to a defective nozzle that is not ejecting, the drive waveform selection unit selects a drive waveform corresponding to the second droplet amount as the drive waveform for the target pixel.

Images