JP7380237B2 - Image processing device, image forming device, and image processing program - Google Patents

Description

The present invention relates to an image processing device, an image forming device, and an image processing program.

For example, Patent Document 1 describes an image processing device that can obtain an output image with good graininess. This image processing device includes an acquisition means for acquiring first image data of a first resolution obtained by error diffusion processing and composed of a plurality of pixels including white pixels and colored pixels. Be prepared. The image processing device also assigns a plurality of dots including at least one of white dots and colored dots to each of the plurality of pixels of the first image data, and converts the first image data into a second image with a second resolution larger than the first resolution. A resolution conversion means for converting into image data is provided. Further, the resolution converting means changes the ratio of colored dots to white dots to be assigned to the colored pixel of interest in accordance with the proportion of colored pixels in a predetermined area including the colored pixel of interest of the first image data.

JP2019-149786A

Conventionally, so-called isolated point correction is sometimes performed in which a pixel of interest is corrected according to the number of white pixels surrounding the pixel of interest. In this case, some pixels are corrected and some pixels are not corrected, even though the proportion of colored pixels in a certain area is approximately the same. Therefore, density unevenness occurs in the output image.

The present invention provides an image processing device, an image forming device, and an image processing program that can suppress the occurrence of density unevenness compared to the case where a pixel of interest is corrected according to the number of white pixels surrounding the pixel of interest. The purpose is to provide.

In order to achieve the above object, an image processing device according to a first aspect includes a processor, and the processor processes image data that includes a plurality of white pixels and a plurality of colored pixels into a focused colored pixel. A first region including a pixel and a plurality of pixels around the pixel of interest is set, and all of the plurality of pixels in the first region are white pixels or less than a predetermined number of the plurality of pixels are colored pixels. , a second region larger than the first region is set for the image data, and if a proportion of colored pixels occupying the second region is less than or equal to a threshold value, the pixel of interest is corrected.

Further, in the image processing apparatus according to a second aspect, in the image processing apparatus according to the first aspect, when the proportion of colored pixels occupying the second area is larger than the threshold value, the processor corrects the pixel of interest. Not performed.

Further, in the image processing device according to a third aspect, in the image processing device according to the second aspect, when the processor determines that at least the predetermined number of the plurality of pixels in the first area are colored pixels, The second area is not set.

Further, in the image processing device according to a fourth aspect, in the image processing device according to any one of the first to third aspects, the first area is n×n (n is an odd number greater than or equal to 3), and the second region is an m×m region (m is an odd number greater than n) centered on the pixel of interest.

Further, in the image processing apparatus according to a fifth aspect, in the image processing apparatus according to the fourth aspect, the predetermined number becomes a larger value as n of the first area becomes larger, and the threshold value becomes a larger value than the first area. The larger m in the two regions is, the larger the value becomes.

Further, in the image processing device according to a sixth aspect, in the image processing device according to any one of the first to fifth aspects, each of the plurality of pixels constituting the image data is assigned a plurality of dots. Each of the plurality of dots is associated with a light emitting element included in the exposure apparatus, and the white pixel is a white dot that turns off the light emitting element. The pixel is a pixel, and the colored pixel is a pixel to which a colored dot, which is a dot that lights up a light emitting element, is assigned to the plurality of dots, and the correction of the pixel of interest is a pixel in which a plurality of colored dots, which are dots that light up a light emitting element, are assigned to the plurality of dots, and the correction of the pixel of interest is performed using a plurality of colored dots assigned to the pixel of interest. It is said that this is a correction that changes at least one of the dots to a white dot.

Furthermore, in order to achieve the above object, an image forming apparatus according to a seventh aspect includes an image processing apparatus according to any one of the first to sixth aspects, and image data acquired from the image processing apparatus. and an image output unit that outputs an image based on the image.

Furthermore, in order to achieve the above object, the image processing program according to the eighth aspect includes a pixel of interest that is a colored pixel of interest and a pixel of interest that is a colored pixel of interest for image data including a plurality of white pixels and a plurality of colored pixels. If a first region including a plurality of surrounding pixels is set, and all of the plurality of pixels in the first region are white pixels or less than a predetermined number of the plurality of pixels are colored pixels, the image data is Then, a second region larger than the first region is set, and when a proportion of colored pixels occupying the second region is less than or equal to a threshold value, the computer is caused to correct the pixel of interest.

According to the first aspect, the seventh aspect, and the eighth aspect, the occurrence of density unevenness can be suppressed compared to the case where the pixel of interest is corrected according to the number of white pixels surrounding the pixel of interest. It has this effect.

According to the second aspect, it is possible to suppress the intermediate density from becoming thinner by correcting the pixel of interest.

According to the third aspect, there is an effect that the second area can be prevented from being set unnecessarily.

According to the fourth aspect, the first region and the second region can be easily set compared to the case where the n×n region is not applied to the first region and the m×m region is not applied to the second region. , has the effect of

According to the fifth aspect, it is possible to determine whether or not to correct the pixel of interest depending on the sizes of the first region and the second region.

According to the sixth aspect, there is an effect that the pixel of interest can be made less noticeable and graininess can be improved.

FIG. 1 is a block diagram illustrating an example of an electrical configuration of an image forming apparatus according to an embodiment. FIG. 1 is a block diagram illustrating an example of a functional configuration of an image processing device according to an embodiment. FIG. 3 is a diagram for explaining error diffusion processing according to the embodiment. (A) is a diagram showing an example of an arrangement of a plurality of dots assigned to one pixel of image data. (B) is a diagram showing an example of a lighting pattern for colored pixels. (C) is a diagram showing an example of a lighting pattern for white pixels. FIG. 7 is a diagram for explaining isolated point correction processing according to a comparative example. (A) is a diagram showing image data according to a comparative example. (B) is a diagram showing an arrangement pattern of colored pixels corresponding to an uncorrected portion of image data according to a comparative example. (C) is a diagram showing an arrangement pattern of colored pixels corresponding to a corrected portion of image data according to a comparative example. (A) and (B) are diagrams for explaining isolated point correction processing according to the embodiment. 3 is a flowchart illustrating an example of the flow of processing by an image processing program according to an embodiment. FIG. 6 is a diagram illustrating an example of a state in which a pixel of interest is selected by a first window. It is a figure showing an example of the lighting pattern of the light emitting element concerning an embodiment.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to drawings, an example of the form for implementing this invention is demonstrated in detail.

FIG. 1 is a block diagram showing an example of the electrical configuration of an image forming apparatus 20 according to this embodiment.

As shown in FIG. 1, the image forming apparatus 20 according to the present embodiment includes an image processing apparatus 10, a display section 21, an operation section 22, an image reading section 23, an image output section 24, and a communication section 25. , is equipped with. The image processing device 10 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, an input/output interface (I/O) 14, and a storage section 15. We are prepared. The image processing apparatus 10 according to the present embodiment is configured as an image processing section included in the image forming apparatus 20.

The CPU 11, ROM 12, RAM 13, and I/O 14 are each connected via a bus. Each functional section including a storage section 15, a display section 21, an operation section 22, an image reading section 23, an image output section 24, and a communication section 25 is connected to the I/O 14. Each of these functional units can communicate with the CPU 11 via the I/O 14.

A control unit is configured by the CPU 11, ROM 12, RAM 13, and I/O 14. The control unit may be configured as a sub-control unit that controls a part of the operation of the image forming apparatus 20, or may be configured as a part of a main control unit that controls the entire operation of the image forming apparatus 20. . For example, an integrated circuit such as an LSI (Large Scale Integration) or an IC (Integrated Circuit) chipset is used for a part or all of each block of the control section. Individual circuits may be used for each of the above blocks, or a part or all of them may be integrated. Each of the blocks described above may be provided integrally, or some blocks may be provided separately. Moreover, in each of the above-mentioned blocks, a part thereof may be provided separately. The integration of the control section is not limited to LSI, but a dedicated circuit or a general-purpose processor may also be used.

As the storage unit 15, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), a flash memory, etc. are used. The storage unit 15 stores an image processing program 15A according to the present embodiment. Note that this image processing program 15A may be stored in the ROM 12.

The image processing program 15A may be installed in the image forming apparatus 20 in advance, for example. The image processing program 15A may be realized by being stored in a nonvolatile storage medium, or distributed via a network, and installed in the image forming apparatus 20 as appropriate. Note that examples of nonvolatile storage media include CD-ROM (Compact Disc Read Only Memory), magneto-optical disk, HDD, DVD-ROM (Digital Versatile Disc Read Only Memory), flash memory, memory card, etc. Ru.

For example, a liquid crystal display (LCD), an organic EL (electro luminescence) display, or the like is used for the display unit 21. The display unit 21 may integrally include a touch panel. The operation unit 22 is provided with various operation keys such as a numeric keypad and a start key. The display unit 21 and the operation unit 22 receive various instructions from the user of the image forming apparatus 20. These various instructions include, for example, an instruction to start reading a document, an instruction to start copying a document, and the like. The display unit 21 displays various information such as the results of processing executed in response to instructions received from the user and notifications regarding the processing.

The image reading unit 23 captures the originals placed on the paper feed tray of an automatic document feeder (not shown) provided at the top of the image forming apparatus 20 one by one, optically reads the imported originals, and obtains image information. get. Alternatively, the image reading unit 23 optically reads a document placed on a document table such as a platen glass to obtain image information.

The image output unit 24 outputs image information obtained by reading by the image reading unit 23 or image information obtained from an external personal computer (PC) or the like connected via a network (not shown). The image based on the image is output to a recording medium such as paper (hereinafter simply referred to as "paper"). Note that in this embodiment, an electrophotographic method will be exemplified and explained as a method for outputting an image.

When the image output method is an electrophotographic method, the image output section 24 includes a photosensitive drum, a charging device, an exposure device, a developing device, a transfer device, and a fixing device. The charging device applies a voltage to the photoreceptor drum to charge the surface of the photoreceptor drum. The exposure device forms an electrostatic latent image on the photoreceptor drum by exposing the photoreceptor drum charged by the charging device to light according to image information. The developing device forms a toner image on the photoreceptor drum by developing the electrostatic latent image formed on the photoreceptor drum with toner. The transfer device transfers the toner image formed on the photoreceptor drum onto paper. The fixing device fixes the toner image transferred to the paper by applying heat and pressure.

The communication unit 25 is connected to a network such as the Internet, a LAN (Local Area Network), or a WAN (Wide Area Network), and is capable of communicating with an external PC or the like via the network.

By the way, as mentioned above, when performing so-called isolated point correction in which the pixel of interest is corrected according to the number of white pixels surrounding the pixel of interest, even though the proportion of colored pixels in a certain area is approximately the same, , some pixels are corrected and some pixels are not corrected. Therefore, density unevenness occurs in the output image.

Therefore, the CPU 11 of the image processing device 10 according to the present embodiment functions as each unit shown in FIG. 2 by writing the image processing program 15A stored in the storage unit 15 into the RAM 13 and executing it. This CPU 11 is an example of a processor.

FIG. 2 is a block diagram showing an example of the functional configuration of the image processing device 10 according to this embodiment.

As shown in FIG. 2, the CPU 11 of the image processing device 10 according to this embodiment functions as a color conversion section 11A, an error diffusion section 11B, and a correction section 11C.

The color conversion unit 11A according to the present embodiment converts the RGB (R: red, G: green, B: blue) data acquired by the image reading unit 23 into CMYK (C: cyan, M: magenta, Y: yellow). K: black) is converted into CMYK data that specifies the color of each pixel in the color space.

The error diffusion unit 11B according to this embodiment converts CMYK color data into binary color data by error diffusion processing. Each binary color data is binary image data represented by a white pixel with a density of 0 (zero) and a colored pixel with a predetermined density. For example, K color (black) data is binary image data represented by white pixels and black pixels.

Here, error diffusion processing used for binarization will be described with reference to FIG. 3.

FIG. 3 is a diagram for explaining error diffusion processing according to this embodiment.

Error diffusion processing is a halftone processing method that is superior to dither processing in that moiré does not occur in the output image. In the example of FIG. 3, as indicated by the dotted arrow, processing is started from the upper left corner of the image data to be processed, and processing is performed from left to right and from top to bottom. The pixel G to be processed next is shaded. When the pixel value f of the pixel G is larger than the threshold value, the pixel G is made a white pixel, and when the pixel value f of the pixel G is less than or equal to the threshold value, the pixel G is made a colored pixel.

When pixel G is a white pixel or a colored pixel, an error occurs between the original pixel value (=f) and the processed pixel value. For example, assume that the pixel value of a colored pixel is 255, the pixel value of a white pixel is 0, and the threshold value is 127. In this case, if pixel G is a colored pixel, the error is e=(f-255), and if pixel G is a white pixel, the error is e=f. This error e is diffused to surrounding pixels G1 to G4 before processing. For example, a part of the error e is added to the pixel value f1 of the pixel G1 to be processed next.

The correction unit 11C according to this embodiment performs isolated point correction processing on the image data after the error diffusion processing. The details of the isolated point correction process according to this embodiment will be described later.

Here, the image data to be corrected is represented, for example, as binary color data obtained by converting CMYK color data by error diffusion processing. This image data includes a plurality of white pixels and a plurality of colored pixels. As described above, a white pixel is a pixel with a density of 0 (zero), and a colored pixel is a pixel with a predetermined density. A plurality of dots are assigned to one pixel of image data.

On the other hand, the exposure device included in the image output section 24 uses, for example, a print head in which a plurality of light emitting elements are arranged in the width direction of the paper. In this type of exposure apparatus, one dot is associated with one light emitting element. Note that, as an example of the light emitting element, an LED (Light Emitting Diode) or the like is used. In other words, each dot of the image data represents information on turning on and off the light emitting element.

The above dots include white dots and colored dots. The white dots are dots that turn off the light emitting elements, and the colored dots are dots that turn on the light emitting elements. By lighting up the light emitting elements in accordance with the colored dots, one dot is exposed and an electrostatic latent image of one dot is formed. Colored dots are formed on the paper by toner. The above-mentioned white pixel is a pixel in which a white dot is assigned to a plurality of dots, and the colored pixel is a pixel in which a colored dot is assigned to a plurality of dots.

Next, the relationship between pixels and dots will be specifically explained with reference to FIGS. 4(A) to 4(C).

FIG. 4A is a diagram showing an example of an arrangement of a plurality of dots assigned to one pixel of image data. Here, the number of dots assigned to one pixel is eight. The eight dots are arranged in two rows and four columns. Each of the eight dots is assigned a number from 0 to 7.

FIG. 4(B) is a diagram showing an example of a lighting pattern for colored pixels, and FIG. 4(C) is a diagram showing an example of a lighting pattern for white pixels.

Here, the lighting pattern represents an arrangement pattern of white dots and colored dots among a plurality of dots assigned to one pixel of image data, that is, a drawing pattern. In the colored pixels of the image data, all of the plurality of dots are colored dots, as shown in FIG. 4(B). On the other hand, in the white pixels of the image data, all of the plurality of dots are white dots, as shown in FIG. 4(C).

The image output unit 24 according to the present embodiment outputs an image onto paper based on the image data acquired from the image processing device 10.

Note that the functions of each part of the image processing device 10 (color conversion unit 11A, error diffusion unit 11B, and correction unit 11C) are not limited to software, but are, for example, dedicated software such as ASIC (Application Specific Integrated Circuit). It may also be realized by hardware.

Next, an outline of isolated point correction processing according to a comparative example will be described with reference to FIGS. 5 and 6.

FIG. 5 is a diagram for explaining isolated point correction processing according to a comparative example.

As shown in FIG. 5, the pixel located at the center of the window W, which is an area of 3 pixels x 3 pixels, is defined as the pixel of interest Px. The pixel of interest Px is a colored pixel. In the isolated point correction process according to the comparative example, the pixel of interest Px is corrected according to the number of white pixels around the pixel of interest Px. For example, if all eight pixels surrounding the pixel of interest Px in the window W are white pixels, the pixel of interest Px is determined to be an isolated point. In the example of FIG. 5, if the sum of the pixel values of the surrounding eight pixels is sum, then sum=w[2][2]+w[2][3]+w[2][4]+w[3][2] +w[3][4]+w[4][2]+w[4][3]+w[4][4]. When sum=0 (zero), the pixel of interest Px is determined to be an isolated point. Furthermore, if sum≧threshold, the window W is determined to be a solid area. Further, if 0<sum<threshold, the window W is determined to be a halftone area.

When the pixel of interest Px is determined to be an isolated point, a correction is performed to change at least one of the plurality of colored dots assigned to the pixel of interest Px to a white dot, that is, a correction is performed to change the lighting pattern of the light emitting element. . On the other hand, if some of the eight pixels surrounding the pixel of interest Px in the window W are colored pixels, the pixel of interest Px is not determined to be an isolated point, and no correction is performed on the pixel of interest Px. The purpose of this isolated point correction processing is to improve graininess by applying it to areas where colored pixels are relatively conspicuous, such as highlight areas with low image density.

FIG. 6A is a diagram showing image data according to a comparative example. Moreover, FIG. 6(B) is a diagram showing an arrangement pattern of colored pixels corresponding to the uncorrected portion R1 of the image data according to the comparative example. Further, FIG. 6C is a diagram showing an arrangement pattern of colored pixels corresponding to the corrected portion R2 of the image data according to the comparative example.

The image data shown in FIG. 6(A) has a periodic pattern. When the isolated point correction process according to the comparative example is applied to this image data, an uncorrected portion R1 and a corrected portion R2 are generated.

In other words, in the case of the uncorrected portion R1, as shown in FIG. 6(B), two of the eight pixels surrounding the pixel of interest Px in the window W are colored pixels, so it is not determined to be an isolated point, and the isolated point is corrected. No processing takes place. On the other hand, in the case of the portion R2 to be corrected, as shown in FIG. 6(C), all eight pixels surrounding the pixel of interest Px in the window W are white pixels, so it is determined to be an isolated point, and the isolated point correction process is performed. It will be done. However, in the example of FIG. 6(B), the ratio of colored pixels in the predetermined area (for example, a 7 pixel x 7 pixel area) is 13/49, and in the example of FIG. For example, the ratio of colored pixels to an area of 7 pixels x 7 pixels is 14/49. In other words, even though the proportion of colored pixels occupying a predetermined area is approximately the same, a portion R1 that is not corrected and a portion R2 that is corrected occur. If such image data is output, density unevenness will appear. This density unevenness occurs particularly prominently in an image having a periodic pattern as shown in FIG. 6(A).

Next, isolated point correction processing according to this embodiment will be specifically described with reference to FIGS. 7(A) and 7(B).

FIGS. 7A and 7B are diagrams for explaining isolated point correction processing according to this embodiment.

For example, as shown in FIG. 7A, the correction unit 11C according to the present embodiment corrects the image data after the error diffusion process, as shown in FIG. Set window W1. The pixel of interest Px is a colored pixel. The first window W1 is an example of a first area. The first window W1 is an area of n pixels by n pixels (n is an odd number of 3 or more) centered on the pixel of interest Px. In the example of FIG. 7A, the first window W1 is an area of 3 pixels x 3 pixels, so the number of pixels surrounding the pixel of interest Px is eight. Note that the size of the first window W1 is not limited to 3 pixels x 3 pixels, but may be 5 pixels x 5 pixels, 7 pixels x 7 pixels, or the like.

When all of the plurality of pixels in the first window W1 are white pixels or less than a predetermined number of the plurality of pixels are colored pixels, the correction unit 11C determines the pixel of interest Px to be an isolated point, and corrects the above image data. Then, a second window W2 larger than the first window W1 is set. Note that, when the size of the first window W1 is 3 pixels x 3 pixels, the predetermined number is appropriately set, for example, in the range of 2 or more and 5 or less. Further, the second window W2 is an example of a second area. The second window W2 is an area of m pixels×m pixels (m is an odd number larger than n) centered on the pixel of interest Px. In the example of FIG. 7A, the second window W2 is an area of 7 pixels×7 pixels.

On the other hand, if more than the predetermined number of pixels in the first window W1 are colored pixels, the correction unit 11C does not determine the pixel of interest Px to be an isolated point and does not set the second window W2. . That is, the pixel of interest Px is not corrected. Note that the predetermined number is not limited to a fixed value, and may be set to a larger value as n of the first window W1 becomes larger.

The correction unit 11C corrects the pixel of interest Px when the second window W2 is set and the proportion of colored pixels occupying the second window W2 is equal to or less than the threshold value. This threshold value is desirably set to, for example, about 1/4 of the size of the second window W2. If the size of the second window W2 is 7 pixels x 7 pixels, the threshold value is 1/4 of 7 pixels x 7 pixels = 49 pixels, for example, 12/49. That is, the above threshold value may be set to a larger value as m of the second window W2 becomes larger.

In the example of FIG. 7A, all of the surrounding eight pixels in the first window W1 are white pixels, and the ratio of colored pixels in the second window W2 (=4/49) is the threshold (=12/ 49) Since the following is true, the pixel of interest Px is corrected. Note that, as described above, the correction here is a correction that changes at least one of the plurality of colored dots assigned to the pixel of interest Px to a white dot, that is, a correction that changes the lighting pattern of the light emitting element. .

On the other hand, the correction unit 11C does not correct the pixel of interest Px when the proportion of colored pixels occupying the second window W2 is larger than the threshold value. In other words, even if the pixel of interest Px is determined to be an isolated point, isolated point correction is not performed.

In the example of FIG. 7B, all of the surrounding eight pixels in the first window W1 are white pixels, and the ratio of colored pixels in the second window W2 (=13/49) is the threshold value (=12/49). 49), the pixel of interest Px is not corrected.

Here, as shown in FIG. 7A, the isolated point correction process is performed in an area where the pixel of interest Px is an isolated point and where the proportion of colored pixels is relatively low, that is, where the colored pixels are relatively It is intended to be applied to conspicuous highlighted areas. Therefore, as shown in FIG. 7B, even if the pixel of interest Px is an isolated point, the pixel of interest Px is relatively inconspicuous in a region where the proportion of colored pixels is relatively high, so it does not need to be applied.

By applying the isolated point correction processing according to this embodiment, the occurrence of the above-described density unevenness is suppressed. Particularly, when applied to image data having a periodic pattern as shown in FIG. 6A, a remarkable effect of suppressing density unevenness can be obtained. Furthermore, the isolated point correction processing according to this embodiment also prevents the intermediate density from becoming thinner.

Next, with reference to FIG. 8, the operation of the image processing apparatus 10 according to this embodiment will be described.

FIG. 8 is a flowchart showing an example of the flow of processing by the image processing program 15A according to the present embodiment.

In this example, a case will be described in which isolated point correction processing according to the present embodiment is performed on image data after error diffusion processing.

In step 100 of FIG. 8, the CPU 11 sets the first window W1 shown in FIG. 7(A) or FIG. 7(B), as an example, for the image data after the error diffusion process.

In step 101, the CPU 11 selects the pixel of interest Px within the first window W1 set in step 100. In this embodiment, by moving the first window W1, each pixel of the image data is sequentially selected as the pixel of interest Px.

FIG. 9 is a diagram showing an example of a selection state of the pixel of interest Px by the first window W1.

As shown in FIG. 9, the first window W1 of 3 pixels x 3 pixels is moved pixel by pixel with respect to the image data 50 acquired by the error diffusion process so that each pixel becomes the pixel of interest Px in turn. For example, selection starts from the pixel at the upper left corner of the image data 50, and the first window W1 is moved from left to right and from top to bottom.

The first window W1 is arranged on the image data 50 so that one pixel overlaps the pixel of interest Px. In this example, the center pixel of the first window W1 overlaps the pixel of interest Px. Furthermore, the first window W1 includes a pixel of interest Px and eight surrounding pixels adjacent to the pixel of interest Px. The size of the first window W1 is not limited to 3 pixels x 3 pixels. For example, the size of the first window W1 may be changed to 5 pixels x 5 pixels, 9 pixels x 5 pixels, etc.

In step 102, the CPU 11 determines whether the pixel of interest Px is a colored pixel. If it is determined that the pixel of interest Px is a colored pixel (in the case of an affirmative determination), the process proceeds to step 103, and if it is determined that the pixel of interest Px is not a colored pixel (in the case of a negative determination), the process proceeds to step 108.

In step 103, the CPU 11 determines whether the pixel of interest Px is an isolated point. Specifically, as described above, all of the surrounding pixels (for example, 8 surrounding pixels) of the pixel of interest Px in the first window W1 are white pixels, or less than a predetermined number of surrounding pixels are colored pixels. Determine whether or not. When it is determined that the pixel of interest Px is an isolated point, that is, that all of the surrounding pixels of the pixel of interest Px are white pixels or less than a predetermined number of surrounding pixels are colored pixels (in case of affirmative determination), The process moves to step 104. On the other hand, if it is determined that the pixel of interest Px is not an isolated point, that is, a predetermined number or more of the surrounding pixels of the pixel of interest Px are colored pixels (in the case of a negative determination), the process moves to step 108.

In step 104, the CPU 11 sets, for example, the second window W2 shown in FIG. 7(A) or FIG. 7(B) above for the image data. The second window W2 is larger than the first window W1, for example, 7 pixels×7 pixels.

In step 105, the CPU 11 calculates the proportion of colored pixels occupying the second window W2 set in step 104. For example, in the example of FIG. 7(A), the ratio of colored pixels is calculated as 4/49, and in the example of FIG. 7(B), the ratio of colored pixels is calculated as 13/49.

In step 106, the CPU 11 determines whether the proportion of colored pixels in the second window W2 calculated in step 105 is less than or equal to a threshold value. If it is determined that the proportion of colored pixels occupying the second window W2 is less than or equal to the threshold value (in the case of an affirmative determination), the process moves to step 107, and if it is determined that the proportion of colored pixels occupying the second window W2 is greater than the threshold value. (In case of negative determination), the process moves to step 108.

In step 107, the CPU 11 corrects the pixel of interest Px. Specifically, a correction is performed to change at least one of the plurality of colored dots assigned to the pixel of interest Px to a white dot, that is, a correction is performed to change the lighting pattern of the light emitting element.

FIG. 10 is a diagram showing an example of a lighting pattern of a light emitting element according to this embodiment.

The example of the lighting pattern shown in FIG. 10 shows an arrangement pattern of white dots and colored dots among the eight dots assigned to one pixel shown in FIG. 4A described above. FIG. 10 illustrates nine types of lighting patterns numbered 1 to 9. In No. 1, all of the plurality of dots are white dots, similar to the above-described FIG. 4(C). The ratio of colored dots to all dots (eight in the example of FIG. 10) is 0/8. In No. 9, all of the plurality of dots are colored dots, similar to the above-described FIG. 4(B). The ratio of colored dots to all dots is 8/8. From No. 2 to No. 8, the ratio of colored dots to all dots changes from 1/8 to 7/8.

In No. 2, the number of colored dots is one, and the ratio of colored dots to all dots is 1/8. In No. 3, the number of colored dots is 2, and the ratio of colored dots to all dots is 2/8. In No. 4, the number of colored dots is 3, and the ratio of colored dots to all dots is 3/8. In No. 5, the number of colored dots is 4, and the ratio of colored dots to all dots is 4/8. In No. 6, the number of colored dots is 5, and the ratio of colored dots to all dots is 5/8. In No. 7, the number of colored dots is 6, and the ratio of colored dots to all dots is 6/8. In No. 8, the number of colored dots is 7, and the ratio of colored dots to all dots is 7/8.

For example, the relationship between the number of colored pixels included in the surrounding pixels of the pixel of interest Px in the first window W1 and the lighting pattern may be determined in advance. Specifically, if the number of colored pixels is less than the first threshold, "No. 5 lighting pattern (ratio of colored dots is 4/8)" is used, and if the number of colored pixels is greater than or equal to the first threshold but less than the second threshold, If the number of colored pixels is equal to or higher than the second threshold, it is called "lighting pattern No. 7 (ratio of colored dots is 6/8)" and "lighting pattern No. 8 (ratio of colored dots is 7/8)". Thus, the relationship between the number of colored pixels and the lighting pattern may be determined in advance, and a lighting pattern corresponding to the number of detected colored pixels may be obtained. In this case, the smaller the number of colored pixels in the first window W1, the lower the proportion of colored dots, that is, the higher the proportion of white dots, a lighting pattern is obtained. Note that the first threshold value and the second threshold value (>first threshold value) are integers of 1 or more. Moreover, the threshold value is not limited to a plurality of values, and may be one.

In step 108, the CPU 11 determines whether or not there is the next pixel in the image data. If it is determined that there is a next pixel (in the case of a positive determination), the process returns to step 100 and the process is repeated; if it is determined that there is no next pixel (in the case of a negative determination), a series of processes by the image processing program 15A are performed. finish.

As described above, according to the present embodiment, if the pixel of interest is an isolated point and the proportion of colored pixels is relatively low, the pixel of interest is corrected; , and in a region where the proportion of colored pixels is relatively high, the pixel of interest is not corrected. This suppresses the occurrence of density unevenness.

Note that in each of the above embodiments, the processor refers to a processor in a broad sense, and includes a general-purpose processor (e.g., CPU: Central Processing Unit, etc.) and a dedicated processor (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.).

Further, the operation of the processor in each of the above embodiments may be performed not only by one processor, but also by a plurality of processors located at physically separate locations. Further, the order of each operation of the processor is not limited to the order described in each of the above embodiments, and may be changed as appropriate.

The image processing apparatus according to the embodiment has been described above as an example. The embodiment may be in the form of a program for causing a computer to execute the functions of each unit included in the image processing apparatus. Embodiments may be in the form of a computer readable storage medium storing this program.

In addition, the configuration of the image processing apparatus described in the above embodiment is merely an example, and may be changed according to the situation without departing from the spirit of the invention.

Furthermore, the process flow of the program described in the above embodiment is only an example, and unnecessary steps may be deleted, new steps may be added, or the processing order may be changed without departing from the main purpose. good.

Further, in the above embodiment, a case has been described in which the processing according to the embodiment is realized by a software configuration using a computer by executing a program, but the present invention is not limited to this. The embodiments may be realized by, for example, a hardware configuration or a combination of a hardware configuration and a software configuration.

10 Image processing device 11 CPU
11A Color conversion section 11B Error diffusion section 11C Correction section 12 ROM
13 RAM
14 I/O
15 Storage unit 15A Image processing program 20 Image forming device 21 Display unit 22 Operation unit 23 Image reading unit 24 Image output unit 25 Communication unit

Claims (8)

Equipped with a processor,
The processor includes:
For image data including a plurality of white pixels and a plurality of colored pixels, a first region including a pixel of interest which is a colored pixel of interest and a plurality of pixels around the pixel of interest is set, and the If all of the plurality of pixels are white pixels or less than a predetermined number of the plurality of pixels are colored pixels, a second region larger than the first region is set for the image data, and the second region is An image processing device that corrects the pixel of interest when the proportion of colored pixels in the pixel of interest is equal to or less than a threshold value. The image processing device according to claim 1, wherein the processor does not correct the pixel of interest when the proportion of colored pixels occupying the second region is larger than the threshold value. The image processing device according to claim 2 , wherein the processor does not set the second region if more than the predetermined number of the plurality of pixels in the first region are colored pixels. The first area is an n×n area (n is an odd number of 3 or more) centered on the pixel of interest,
The image processing device according to any one of claims 1 to 3, wherein the second area is an m×m (m is an odd number greater than n) area centered on the pixel of interest. The predetermined number becomes a larger value as n of the first region becomes larger,
The image processing device according to claim 4, wherein the threshold value becomes a larger value as m of the second region becomes larger. Each of the plurality of pixels constituting the image data is assigned a plurality of dots,
Each of the plurality of dots is associated with a light emitting element included in the exposure device,
The white pixel is a pixel in which a white dot that turns off a light emitting element is assigned to the plurality of dots,
The colored pixel is a pixel in which a colored dot, which is a dot that lights up a light emitting element, is assigned to the plurality of dots,
The image processing device according to any one of claims 1 to 5, wherein the correction of the pixel of interest is a correction of changing at least one of a plurality of colored dots assigned to the pixel of interest to a white dot. An image processing device according to any one of claims 1 to 6,
an image output unit that outputs an image based on the image data acquired from the image processing device;
An image forming apparatus equipped with For image data including a plurality of white pixels and a plurality of colored pixels, a first region including a pixel of interest which is a colored pixel of interest and a plurality of pixels around the pixel of interest is set, and the If all of the plurality of pixels are white pixels or less than a predetermined number of the plurality of pixels are colored pixels, a second region larger than the first region is set for the image data, and the second region is If the proportion of colored pixels in the pixel is below a threshold, correcting the pixel of interest;
An image processing program that is executed by a computer.