Information processing system, information processing method, and computer readable medium

Abstract

The invention discloses an information processing system, an information processing method, and a computer readable medium. The processor performs, in image data including white pixels and colored pixels, an imparting process for imparting, to each of colored pixels around a target pixel, which is a target colored pixel of interest, a weight that is smaller as the distance from the target pixel is, and performs an imparting process for imparting, to each of the colored pixels around the target pixel, a weight that is smaller as the distance from the target pixel is greater than that of the target pixel in a preset region including the target pixel of interest in the image data including the white pixels and the colored pixels. When the sum of the weights of the colored pixels around the pixel of interest is less than a threshold value, the pixel of interest is corrected.

Description

Technical Field

[0001] The present invention relates to an information processing system, an information processing method and a computer readable medium. Background Art

[0002] Japanese Patent Publication No. 2019-149786 discloses a method for obtaining an output image with good granularity when converting a binary image to an image with a higher resolution. In this method, the ratio of colored points to white points assigned to the colored pixel of interest is changed according to the proportion of the colored pixels in a predetermined area including the colored pixel of interest.

[0003] In the method of Japanese Patent Publication No. 2019-149786, when observing a second area larger than a preset area (referred to as a first area), although the number of colored pixels in the second area is roughly the same, sometimes the correction of the pixel of interest is switched according to the difference in the number of colored pixels in the first area. This causes uneven density.

[0004] In response to this, in the method disclosed in Japanese Patent Application Laid-Open No. 2021-114662, when the number of colored pixels in the first area is below a specified value, the number of colored pixels in the second area wider than the first area is investigated, and when the number is below a threshold, the colored pixel of interest is determined to be an isolated point and corrected. When the number is greater than the threshold, the colored pixel of interest is not corrected.

[0005] Although the method of Japanese Patent Gazette No. 2021-114662 uses two stages of areas of different sizes depending on the situation, the basic idea is to determine whether the focus pixel needs to be corrected based on the number or proportion of colored pixels in a pre-set area including the focus colored pixel (hereinafter referred to as "focus pixel"). Summary of the invention

[0006] When a binary image is printed by a printing device with a large dot gain due to error diffusion, the size of the dots printed corresponding to the pixels of the image becomes larger, for example, dots that are significantly larger than the pixels are printed. Therefore, the closer the surrounding colored pixels are to the pixel of interest, the easier it is for the dots of the colored pixels to overlap with the dots of the pixel of interest.

[0007] In the case where there is no point overlapping with the point of the pixel of interest among the points of the surrounding colored pixels, the point of the pixel of interest is easily conspicuous as an isolated point, and the graininess looks poor. Therefore, in this case, the necessity of correction is high. However, in the method of not performing isolated point correction if the number or ratio of colored pixels in the area is greater than the threshold, and performing isolated point correction if it is less than the threshold, even in this case, if there are more distant colored pixels in the area than the threshold, no correction is performed.

[0008] An object of the present invention is to obtain an output image with a better graininess than a method of controlling whether to correct a pixel of interest based on the number or ratio of colored pixels in a preset area including the pixel of interest.

[0009] According to a first aspect of the present invention, there is provided an information processing system comprising a processor, wherein the processor performs a weighting process on each of the colored pixels around the focus pixel in a predetermined area including a focus pixel in image data including white pixels and colored pixels, wherein the processor assigns a smaller weight the farther away from the focus pixel the colored pixels are from the focus pixel, and when the sum of the weights of the respective colored pixels around the focus pixel is less than a threshold value, the focus pixel is corrected.

[0010] According to the second aspect of the present invention, in the information processing system based on the first aspect, the processor calculates the weight assigned to each of the colored pixels around the pixel of interest, the weight being smaller the farther from the pixel of interest, based on the value obtained by raising the baseline weight, which is a real value ranging from 0 to 1 and is smaller the farther from the pixel of interest, to the power of n (n is an integer greater than 1), and by changing n, the degree of reduction in the weight corresponding to the distance from the pixel of interest can be changed.

[0011] According to the third aspect of the present invention, in the information processing system based on the first or second aspect, the processor, in a printing device that prints image data corrected by the image processing device, performs the assignment processing on image data including white pixels and colored pixels of the color for each color used for printing, calculates the sum of the weights of the colored pixels around the pixel of interest, and when the calculated sum of weights is less than a threshold value, if there are pixels in other colors whose sum of weights is above the threshold value, does not correct the pixel of interest, and when there are no pixels in other colors whose sum of weights is above the threshold value, corrects the pixel of interest.

[0012] According to the fourth aspect of the present invention, in the information processing system based on any one of the first to third aspects, the processor uses a value as the threshold value that is smaller as the dot gain of the printing device that prints the image data corrected by the image processing device increases.

[0013] According to a fifth aspect of the present invention, a computer-readable medium is provided, storing a program that enables a computer to execute processing, wherein the processing performs a weighting process on each of the colored pixels around the pixel of interest in a predetermined area including the colored pixel of interest, i.e., the pixel of interest, in image data containing white pixels and colored pixels, wherein the processing assigns a smaller weight the farther away from the pixel of interest the pixel is, and when the sum of the weights of the respective colored pixels around the pixel of interest is less than a threshold value, the pixel of interest is corrected.

[0014] According to the sixth aspect of the present invention, there is provided an information processing method, which performs a weighting process on each of the colored pixels around the focus pixel in a predetermined area including a colored pixel of interest, i.e., a focus pixel, in image data including white pixels and colored pixels, in which a smaller weight is assigned the farther the pixel is from the focus pixel, and corrects the focus pixel when the sum of the weights of the respective colored pixels around the focus pixel is less than a threshold value.

[0015] (Effect)

[0016] According to the first, fifth and sixth aspects, an image with a better graininess can be obtained compared with a method of controlling whether to correct the pixel of interest based on the number or ratio of colored pixels in a preset area including the pixel of interest.

[0017] According to the second aspect, the degree of weight reduction can be adjusted according to the distance from the pixel of interest.

[0018] According to the third aspect, when processing a multi-color image, a change in color balance due to correction can be reduced compared to a method that considers only colored pixels of an image of a color to which the pixel of interest belongs.

[0019] According to the fourth aspect, compared with a case where the same threshold is used regardless of the dot gain of the printing device, an output image with better graininess can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a diagram illustrating the overall functional structure of an image processing apparatus;

[0021] Figure 2 is a diagram showing an example of weight distribution;

[0022] Figure 3is a diagram showing an example of the arrangement of colored pixels within a region;

[0023] Figure 4 is a diagram showing another example of the arrangement of colored pixels within a region;

[0024] Figure 5 is a diagram showing another example of weight distribution;

[0025] Figure 6 is a diagram showing still another example of the arrangement of colored pixels within a region;

[0026] Figure 7 is a diagram illustrating a functional structure of a resolution conversion unit;

[0027] Figure 8 is a diagram illustrating the processing sequence of the resolution conversion unit;

[0028] Fig. 9 A diagram showing an example of arrangement of colored pixels in images of various colors and a multi-color image synthesized from the images;

[0029] Fig.10 is a diagram illustrating the sequence of threshold processing when processing a multi-color image;

[0030] Fig.11 is a diagram illustrating a functional structure of an image processing device including a weight setting UI;

[0031] Fig.12 This is a diagram illustrating the hardware configuration of a computer on which the information processing system is installed. DETAILED DESCRIPTION

[0032] Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0033] <Overall device structure>

[0034] exist Figure 1 The overall functional structure of the image processing device 10 is illustrated in the figure. The image processing device 10 is a device with a printing function, such as a printer, a copier, a multifunction machine (that is, a multifunctional device that has the functions of a printer, a scanner, a copier, a fax machine, etc.). The image processing device 10 includes an information processing system 11 and an image output unit 18. The information processing system 11 is a functional module that performs information processing such as image processing on input image data. The image output unit 18 is a printing device that prints and outputs the input image data onto a recording medium such as paper (hereinafter referred to as "paper"). The printing method of the image output unit 18 is not particularly limited, and it may be, for example, an electronic photography method or an inkjet method.

[0035] The information processing system 11 includes an image input unit 12 , an error diffusion processing unit 14 , and a resolution conversion unit 16 .

[0036] The image input unit 12 receives input of the image data to be targeted. The image input unit 12 is, for example, a scanner that optically reads a manuscript and converts it into electronic image data. Alternatively, the image input unit 12 may be a component that receives a file of image data generated by an external device such as a personal computer and sent via a network or the like. When receiving a file of image data, the image input unit 12 converts the image data contained in the file into a bitmap image.

[0037] In addition, when the color space of the image data input to the image input unit 12 is different from that of the image output unit 18, the image input unit 12 performs color conversion on the input image data to match the color space of the image output unit 18. For example, when the input image data is in RGB format and the image output unit 18 is in CMYK format, the image input unit 12 performs conversion from RGB to CMYK.

[0038] Therefore, the image data transmitted from the image input unit 12 to the error diffusion processing unit 14 is multi-valued (for example, 8 bits for each color) bitmap image data expressed in the color space of the image output unit 18 .

[0039] The error diffusion processing unit 14 converts the multi-valued image data input from the image input unit 12 into binary image data by performing a known error diffusion process on the multi-valued image data. For example, when the input image data is CMYK multi-valued image data, the error diffusion processing unit 14 converts the multi-valued image of each color of CMYK into binary image data. The binary image data of each color is an image represented by white pixels with a density of 0 and colored pixels with a predetermined density.

[0040] The resolution conversion section 16 converts the binary image data of each color output from the error diffusion processing section 14 into image data of the resolution of the image output section 18. The resolution of the binary image data of each color output from the error diffusion processing section 14 is the same as the resolution of the image data input to the image input section 12. On the other hand, the resolution of the image output section 18 for printing may be higher than the resolution of the input image data. Therefore, the resolution conversion section 16 converts the resolution of the binary image data after error diffusion.

[0041] Hereinafter, the resolution of the image data input to the resolution conversion unit 16, that is, the resolution of the binary image data output from the error diffusion processing unit 14, is referred to as the input resolution, and the resolution of the image data output from the resolution conversion unit 16 is referred to as the output resolution. The input resolution is the same as the resolution of the image data input to the image input unit 12. In addition, the output resolution is the same as the resolution of the image output unit 18. In addition, in the following, the image data input to the resolution conversion unit 16 is referred to as the input image data, and the image data output from the resolution conversion unit 16 is referred to as the output image data. In addition, the pixels of the input image data are referred to as the input pixels, and the pixels of the output image data are referred to as the output pixels.

[0042] In addition, the resolution conversion unit 16 also performs isolated point correction when performing resolution conversion. Isolated point correction is a correction for reducing the density of a color pixel that is isolated by only one pixel. That is, when the resolution conversion unit 16 finds a color pixel corresponding to an isolated point from the input image data, it performs correction for reducing the density of the color pixel.

[0043] The isolated point correction in the resolution conversion unit 16 is performed, for example, as follows.

[0044] Consider that the resolution conversion unit 16 converts one input pixel into an m×n (m, n are integers greater than 1) matrix of output pixels. The area of ​​the output pixel is one (m×n)th of the area of ​​the input pixel. If at least one of m or n is greater than 2, the resolution of the output image data is higher than the resolution of the input image data. For example, in the case of converting the resolution of one input pixel into an output pixel group of 2 rows and 4 columns, the number of pixels of the output image data is 8 times the number of pixels of the input image data.

[0045] For input pixels other than isolated points, the resolution conversion unit 16 converts the input pixels into an output pixel group of m rows and n columns having the same value as the input pixel. For example, when the input pixel that is not an isolated point is a white pixel, the resolution conversion unit 16 converts the input pixel into an m×n white output pixel group. In addition, when the input pixel that is not an isolated point is a colored pixel, the resolution conversion unit 16 converts the input pixel into an m×n colored output pixel group. The concentration of each colored output pixel is the same as the concentration of the colored pixel that is the input pixel. Therefore, for input pixels that are not isolated points, the concentration does not change during resolution conversion.

[0046] On the other hand, when it is determined that the input pixel is an isolated point (i.e., an isolated colored pixel), the resolution conversion unit 16 reduces the concentration by changing one or more output pixels in the m-row and n-column output pixel group to white pixels. That is, if it is a colored pixel that is not an isolated point, it is converted to a colored output pixel group of m-row and n-column, but in the case of a colored pixel that is an isolated point, because one or more of the colored output pixel groups of m-row and n-column are replaced with white pixels, the concentration is reduced. In addition, in the isolated point correction, which pixel in the m-row and n-column output pixel group is replaced with a white pixel can be determined according to a pre-set rule. In addition, the determination method of the isolated point of this embodiment will be described in detail later.

[0047] The output image data output from the resolution conversion section 16 is supplied to the image output section 18. The image output section 18 outputs an image on paper in accordance with the output image data.

[0048] <Method of determining isolated points>

[0049] Conventionally, whether a colored pixel of interest (hereinafter referred to as a "pixel of interest") in input image data is an isolated point is determined based on the number of colored pixels in an area of ​​a predetermined size around the pixel of interest.

[0050] In contrast, in this embodiment, the colored pixels around the pixel of interest are given weights whose values ​​decrease as they are farther from the pixel of interest, and whether the pixel of interest is an isolated point is determined based on the sum of the weights of the colored pixels around the pixel of interest. Here, the weight is a value greater than 0.

[0051] In more detail, in this embodiment, when the sum of the weights of the colored pixels around the pixel of interest is less than a preset threshold, the pixel of interest is determined to be an isolated point. The weight of the colored pixel farther from the pixel of interest is smaller, in other words, the weight of the colored pixel closer to the pixel of interest is larger, so the more colored pixels there are near the pixel of interest, the easier it is for the sum of the weights to become larger, and therefore, the pixel of interest is difficult to be determined as an isolated point.

[0052] On the contrary, when there are no colored pixels near the pixel of interest, the pixel of interest is easily determined as an isolated point. For example, even if there are a large number of colored pixels far away from the pixel of interest, but no colored pixels near it, in the printed result, the points of the surrounding colored pixels may not overlap with the points of the pixel of interest at all. In this case, the pixel of interest is easily conspicuous as an isolated point, so it is preferably set as the object of isolated point correction.

[0053] Based on this view, the resolution conversion unit 16 calculates the sum of the weights of the colored pixels around the pixel of interest, and determines whether or not to perform isolated point correction on the pixel of interest by comparing the sum with a threshold value.

[0054] <Weighting Example>

[0055] exist Figure 2 An example of assigning weights to a group of pixels surrounding a pixel of interest is shown in FIG. Figure 2 represents the weights of the pixel positions 210, 220, etc. in the 7×7 pixel area 300 centered on the pixel of interest 200. In this example, the weight W of each pixel position (i, j) is ij It is calculated by the following formula.

[0056] W ij =1 / (i 2 +j 2 ) 1 / 2 ×3

[0057] Here, i and j are the x-coordinate and y-coordinate of each pixel position when the position of the pixel of interest 200 is set to the origin (0, 0). For example, the x-coordinate is positive when it is to the right of the origin and negative when it is to the left, and the y-coordinate is positive when it is above the origin and negative when it is below the origin. ij It is inversely proportional to the distance of the pixel of interest, and the proportionality constant is 3. The relationship that the weight is inversely proportional to the distance and the proportionality constant 3 are merely examples.

[0058] exist Figure 2 In the example, the focus pixel 200 is not the object of the sum of weights, so the weight of the position of the focus pixel 200 is 0, the weight of the pixel position 210 of the adjacent pixel below the focus pixel 200 is 3.0000, and the weight of the pixel position 220 of the lower right adjacent pixel is 2.1213. In addition, in the area 300, the weight of the pixel position 230 of the pixel farthest from the focus pixel 200 and at the lower left corner of the area 300 is 0.7071.

[0059] use Figure 3 For use Figure 2 The following describes an example of determining whether or not to perform isolated point correction when the weight distribution is shown. Figure 3 , a region 300 of 7×7 pixels centered on the pixel of interest 200 is shown. Based on the sum of the weights of the colored pixels in the region 300, it is determined whether or not to correct the pixel of interest 200. Figure 3 (a) shows an example in which there is only one colored pixel 240 at the coordinates (-2, 2) in the region 300, and (b) shows an example in which there is only one colored pixel 250 at the coordinates (-2, 0).

[0060] Circle 202 indicates the periphery of dots formed when the pixel of interest 200 is printed by the image output unit 18. That is, when the pixel of interest 200 is printed by the image output unit 18 without performing isolated dot correction, dots are formed on the paper at the position of the pixel of interest 200, where the inside of circle 202 is filled with ink of the color of the colored pixel. Similarly, circle 242 indicates the periphery of dots formed when the colored pixel 240 is printed by the image output unit 18, and circle 252 indicates the periphery of dots formed when the colored pixel 250 is printed by the image output unit 18. In this example, the dots printed have dots of the input image data (i.e., dots corresponding to the color pixel). Figure 3 The radius of the circle is twice that of the circle with approximately the same area as the pixels shown in the figure, so the dot gain of the image output unit 18 is 2.

[0061] Dot gain is one of the characteristics of a printer, and is the ratio by which a colored pixel (i.e., dot) in the input image is printed as a dot of several times the size. In other words, dot gain is the ratio of the size of the output dot to the size (e.g., radius) of the dot in the input image. The greater the dot gain, the larger the size of the colored pixel in the input image becomes in the output image on the paper.

[0062] exist Figure 3 In the example, the weight distribution uses Figure 2 The weights shown in the example have a threshold value of 1.5 for determining whether isolated point correction is required. That is, if the sum of the weights of the color pixels in the area 300 is less than 1.5, correction is determined, and if it is greater than 1.5, no correction is determined.

[0063] In the example shown in (a), the only colored pixel in the region 300 is the colored pixel 240, so the sum of the weights of the colored pixels in the region 300 is equal to the weight 1.0607 of the colored pixel 240, which is less than the threshold value 1.5. Therefore, the pixel 200 is determined to be the correction target pixel.

[0064] In contrast, in the example shown in (b), the sum of the weights of the colored pixels in the region 300 is equal to the weight 1.5000 of the colored pixel 250, which is equal to or greater than the threshold value 1.5. Therefore, it is determined that the pixel of interest 200 is not to be corrected.

[0065] from Figure 3It can be seen that in the example shown in (a), the point of the focus pixel 200 with the circle 202 as the periphery does not overlap with the point of the surrounding colored pixel 240 (the periphery of the point is the circle 242), while in contrast, in the example shown in (b), the point of the focus pixel 200 overlaps with the point of the surrounding colored pixel 250 (the periphery of the point is the circle 252). Therefore, in the example shown in (a), it can be said that the degree of isolation of the focus pixel 200 from the surrounding colored pixels is high compared with the example shown in (b). Therefore, if there is only one colored pixel 240 or 250 in the area 300, the farther the colored pixel 240 or 250 is from the focus pixel 200, the easier it is to make a decision to correct the focus pixel 200.

[0066] Figure 3 The weight distribution used in the example (see Figure 2 The combination of ) and a threshold value of 1.5 is only an example. In this combination, sometimes it is not possible to perform a correction that meets the user's expectations. Figure 4 This situation is described.

[0067] exist Figure 4 In the example shown, there are four colored pixels 240, 260, 270, and 280 at the coordinates (-2, 2), (-2, -2), (2, -2), and (2, 2) in the region 300. In this case, if the same Figure 3 For the same combination of weight distribution and threshold value as in the example, the total weight in the region 300 is 1.0607×4=4.2428, which is larger than the threshold value 1.5. Therefore, in this case, it is determined that the pixel of interest 200 is not to be corrected.

[0068] Here, the dots when printing the four colored pixels 240, 260, 270, and 280 do not overlap with the dot of the pixel of interest 200. In this case, whether to regard the surrounding of the pixel of interest 200 as having a high degree of color and not perform isolated dot correction, or to perform isolated dot correction because there are no dots overlapping with the dot of the pixel of interest 200, depends on the image quality required by the user. Figure 4 In the example of , when it is desired to perform isolated point correction on the pixel of interest 200, it is necessary to set the combination of weight distribution and threshold value to a combination different from the above example. In this case, for example, Figure 5 The combination of weight distribution and threshold value 1.5 is shown. In this example, such a demand is met by changing only the weight distribution.

[0069] Figure 5 The weight distribution shown is calculated according to the following formula.

[0070] W ij ={1 / (i 2 +j 2 ) 1 / 2} 7 ×16.98

[0071] That is, in Figure 5 In the example, the weight W of each pixel ij The weight is obtained by multiplying the seventh power of the inverse of the distance from the pixel of interest 200 by the proportionality constant 16.98. This weight is inversely proportional to the seventh power of the distance, so it decreases sharply as it moves away from the pixel of interest 200. When this weight distribution is used, Figure 6 As shown in the example, the pixel group outside the 3×3 pixels centered on the pixel of interest 200 is all colored pixels, and the sum of the weights of these colored pixels is also 1.1574. This sum 1.1574 is less than the threshold value 1.5, so it is determined that isolated point correction is performed on the pixel of interest 200. Figure 6 Few examples Figure 4 In the example of , it is also determined that isolated point correction is to be performed.

[0072] <Processing of the resolution conversion unit>

[0073] The above is an explanation of the concept of determining whether or not isolated point correction is necessary using weight distribution and threshold values. Figure 7 An example of the internal structure of the resolution conversion unit 16 according to the idea will be described.

[0074] Figure 7 The illustrated resolution conversion unit 16 includes a multi-valued unit 162 , a weight accumulation unit 164 , and a threshold processing unit 166 .

[0075] The multi-valued unit 162 converts the value of each pixel of the binary image data input from the error diffusion processing unit 14 into a multi-value. This conversion is used to set the value of the pixel to the same real value as the weight so that the weight can be multiplied by the weight in the weight accumulation unit 164. For example, in the case of converting the binary image into an 8-bit multi-value, the multi-valued unit 162 converts the value of the white pixel (i.e., the value is 0) of the binary image into an 8-bit value representing the real value 0.0, and converts the value of the colored pixel (i.e., the value is 1) of the binary image into an 8-bit value representing the real value 1.0. That is, the multi-valued unit 162 converts the binary image of 0 and 1 into an image that is substantially a binary image of 0.0 and 1.0, although it is multi-bit.

[0076] The weight integration unit 164 regards each pixel of the multi-valued image data output from the multi-valued unit 162 as a pixel of interest, and calculates the sum of the weights of the color pixels surrounding the pixel of interest for each pixel of interest.

[0077] The threshold processing unit 166 determines whether to perform isolated point correction on the pixel of interest by comparing the sum of the weights calculated by the weight accumulation unit 164 with the threshold value, and generates an output corresponding to the pixel of interest according to the determination. When generating the output, the threshold processing unit 166 converts one pixel of interest into a matrix of multiple output pixels. Through this action, the input image data is converted into output image data with a higher resolution.

[0078] In this conversion, the threshold processing unit 166 outputs an output pixel group of m×n pixels having the same value as the value of the pixel of interest (i.e., 0 or 1) for the pixel of interest not subjected to isolated point correction. That is, if the pixel of interest is a white pixel, the threshold processing unit 166 outputs an m×n white output pixel group, and if the pixel of interest is a colored pixel, the threshold processing unit 166 outputs an m×n colored output pixel group. In addition, for the pixel of interest subjected to isolated point correction, the threshold processing unit 166 outputs a threshold value for changing some of these output pixel groups to white pixels according to a predetermined rule.

[0079] exist Figure 8 The order of the processing performed by the weight accumulation unit 164 and the threshold processing unit 166 is illustrated in FIG. Figure 3 .

[0080] exist Figure 8 In the order of the weight accumulation unit 164, a focus pixel 100 is selected from the input image data in the prescribed order (S10). Next, the weight accumulation unit 164 determines whether the selected focus pixel 100 is a point (i.e., a colored pixel) (S12). When the focus pixel 100 is not a point, that is, when the focus pixel 100 is a white pixel, the threshold processing unit 166 outputs a white pixel group of m×n pixels as an output pixel group corresponding to the focus pixel (S26).

[0081] In S12, when it is determined that the pixel of interest 100 is a point, the weight accumulation unit 164 clears the value of the accumulation result held as an internal variable to 0 (S14). Next, the weight accumulation unit 164 checks the pixels in the area 300 surrounding the pixel of interest 100 in a predetermined order, and when a colored pixel is found, the weight accumulation unit 164 calculates the pixel of interest 100 based on the weight distribution (e.g. Figure 2 or Figure 5 ) to obtain the weight of the position of the colored pixel. Then, the weight accumulation unit 164 multiplies the value of the colored pixel by its weight, and adds the multiplication result to the accumulation result (S16). Next, the weight accumulation unit 164 determines whether all pixels in the area 300 have been investigated (S18). If there are pixels that have not been investigated, it returns to S16 to process the pixels that have not been investigated.

[0082] When it is determined in S18 that the investigation of all pixels is completed, the value of the sum of the multiplication results of the values ​​of the colored pixels in the area 300 and the weights of the colored pixels is retained in the cumulative result as the internal variable. The value of the colored pixel is a real value of 1.0, and as a result, the final cumulative result represents the sum of the weights of the colored pixels in the area 300. The weight cumulative unit 164 transmits the final cumulative result to the threshold processing unit 166.

[0083] The threshold processing unit 166 determines whether the received final cumulative result is less than the threshold value (S20). When the cumulative result is less than the threshold value (the determination result of S20 is "yes"), the threshold processing unit 166 outputs a point group to which isolated point correction has been implemented as an output pixel group corresponding to the pixel of interest (S22). That is, in this case, the threshold processing unit 166 determines that the pixel of interest is an isolated point and implements isolated point correction. When S22 is performed, the pixel of interest is a point (i.e., a colored pixel), so if it is assumed that isolated point correction is not implemented, the threshold processing unit 166 outputs a point group of m×n pixels as the result of resolution conversion. However, since isolated point correction is implemented in S22, the threshold processing unit 166 converts one or more specified points determined according to the rule of isolated point correction in the point group of these m×n pixels into white pixels and outputs them. As a result, the density of the output pixel group corresponding to the pixel of interest is lower than when isolated point correction is not performed.

[0084] In S22, the intensity of the isolated point correction may be changed according to the final cumulative result, that is, the sum of the weights. That is, the smaller the value of the final cumulative result, the lower the density around the pixel of interest. Therefore, in order to make the density of the pixel of interest lower by the isolated point correction, the number of pixels converted into white pixels in the output pixel group is increased.

[0085] If the result of determination in S20 is "No", that is, the final cumulative result is greater than the threshold, the threshold processing unit 166 outputs the point group of m×n pixels corresponding to the pixel of interest as a result of resolution conversion as it is (S24). That is, in this case, isolated point correction is not performed on the pixel of interest.

[0086] After S22, S24 or S26, the weight accumulation unit 164 determines whether the processing of S10 to S26 has been completed for all pixels of the input image data (S28). If the result of this determination is "no", the weight accumulation unit 164 returns to S10, selects the next pixel of interest from the input image data, and performs the processing after S12 on the pixel of interest.

[0087] When the determination result of S28 is "Yes", the process of resolution conversion of the input image data is completed.

[0088] As described above, in this embodiment, a weight is given to a colored pixel whose distance from the pixel of interest is smaller, and when the sum of the weights of the colored pixel group around the pixel of interest is less than a threshold value, the pixel of interest is subjected to isolated point correction. This method can make a more detailed determination than a method of determining whether isolated point correction is required based on the number of colored pixels around the pixel of interest.

[0089] <Processing of images composed of multiple colors>

[0090] Figure 8 The processing order shown is the order when processing a monochrome image. In contrast, in processing a multi-color image obtained by combining images of multiple colors such as full-color printing, it is necessary to consider the processing of images of multiple colors.

[0091] That is, in the processing of multi-color images, even if the point of the focus pixel of a certain color image is an isolated point in the image, there may be points of other colors nearby. In this case, even if the isolated point correction is performed on the focus pixel, the graininess does not change. On the contrary, in this case, when the isolated point correction is performed, the balance between the color of the focus point and the surrounding points of other colors is destroyed, and the color will look different. Fig. 9 An example of this situation is shown in FIG.

[0092] exist Fig. 9 In the figure, image 400C is a portion of the cyan plate image, and image 400M is a magenta plate of the same portion. Both image 400C and image 400M are binary images after error diffusion processing. Image 400C is composed of white pixels 405 and a plurality of cyan pixels 410C of a predetermined concentration. Image 400M is composed of white pixels 405 and a plurality of magenta pixels 410M of a predetermined concentration. Moreover, image 400A is a multi-color image obtained by synthesizing image 400C and image 400M.

[0093] Here, consider the case where the central cyan pixel 410C in the 7×7 pixels of the image 400C is set as the focus pixel, and determine whether the focus pixel is an isolated point. Here, for the sake of simplicity, if there is one or more colored pixels in the 3×3 pixel area 450 around the focus pixel, the focus pixel is not an isolated point, and if there is no colored pixel, the focus pixel is an isolated point. Fig. 9In the example, when observing the cyan version of the image 400C, the area 450 around the central cyan pixel 410C, which is the pixel of interest, contains only white pixels, and no cyan pixels. Therefore, when only the image 400C is focused on, the pixel of interest is determined to be an isolated point. However, when observing the magenta version of the image 400M, two magenta pixels 410M exist around the position of the pixel of interest in the area 450. In the multi-color image 400A, the pixels 420 at the four corners are colors synthesized from cyan and magenta. In addition, there are magenta pixels 410M at the upper left and lower right of the central cyan pixel 410C (=pixel of interest). In this case, if isolated point correction is performed based only on the cyan version of the image 400C and the cyan concentration of the pixel of interest is reduced, the color balance with the nearby magenta pixel 410M will be different from the balance in the original image.

[0094] Therefore, in this example, when the resolution conversion unit 16 determines whether isolated point correction is required for a pixel of interest of a certain color, it also considers the colored pixels around the pixel of interest in the plates of other colors. Figure 8 Step S22 of the sequence shown is replaced by Fig.10 Steps S220 to S224 are shown below. Fig.10 This processing will be described.

[0095] In this processing sequence, the resolution conversion unit 16 performs Figure 8 The order (where S22 is replaced by Fig.10 ). The processing of each color is performed in parallel, for example. Fig.10 At the time of step S220, the processing of S10 to S20 is completed for all the plates. That is, at this moment, for each color image, the calculation of the final accumulation result (ie, the sum of weights) of the colored pixels around the pixel of interest is completed.

[0096] In S20, when it is determined that the final cumulative result of the colored pixels around the pixel of interest of a certain color is less than the threshold value, the threshold processing unit 166 of the resolution conversion unit 16 compares the final cumulative results calculated for each other color with the threshold value. Furthermore, the threshold processing unit 166 determines whether the final cumulative results of the other colors are all less than the threshold value (S220). When the determination result of S220 is "yes", the threshold processing unit 166 outputs the point group to which the isolated point correction is applied as the output pixel group corresponding to the pixel of interest (S222). When the determination result of S220 is "no", the threshold processing unit 166 outputs the point group of m×n pixels corresponding to the pixel of interest as is, as the result of the resolution conversion (S224). After S222 or S224, the resolution conversion unit 16 enters the processing of S28.

[0097] As described above, in this example, even if the pixel of interest is an isolated point in the image of the color to which the pixel of interest belongs, when images of other colors are also taken into consideration, it is still not an isolated point, and the isolated point correction is not performed on the pixel of interest. By this processing, the deterioration of color balance can be prevented.

[0098] <User-specified weight distribution>

[0099] The weight distribution table used by the weight accumulation unit 164 may also be set to be changeable according to the user's instructions. For example, the weight W is defined by the following formula: ij ,

[0100] W ij ={1 / (i 2 +j 2 ) 1 / 2} n ×k

[0101] It is also possible to prepare a variety of weight distributions by changing the parameters n and k in the definition formula according to the user's instructions. Among them, n is a real number greater than 1, and k is a positive real number. When n=1 and k=1 are used as the reference weight, many weights can be generated by multiplying the reference weight to the nth power by the proportional constant k. In addition, the reference weight illustrated here is just an example after all.

[0102] In this example, the larger the n, the closer the pixel is to the target pixel 200 (see Figure 3 and Figure 4 ) the greater the distance, the steeper the reduction of the weight corresponding to the distance. Even if there are many colored pixels far from the pixel of interest 200 in the region 300, if you want to perform isolated point correction on the pixel of interest, you can increase the value of n.

[0103] Here, if n is simply increased, the sum of the weights may be less than the threshold value even if there are colored pixels very close to the pixel of interest 200, and isolated point correction may be performed on the pixel of interest. If you want to prevent this possibility, you can set the value of the proportional constant k to a larger value.

[0104] The combination of the values ​​of n and k determines in what cases the isolated point correction is performed and in what other cases the isolated point correction is not performed in the distribution of the colored pixels around the pixel of interest 200 .

[0105] In order to realize the image quality (such as graininess) desired by the user, the information processing system 11 of the image processing device 10 may also include a weight setting UI (user interface) 15 (see Fig.11 The weight setting UI 15 displays, for example, on a screen of a display connected to the image processing device 10, a plurality of images (for example, Figure 3 (a) Figure 3 (b) Figure 4 as well as Figure 6 ). Furthermore, the weight setting UI 15 inputs an instruction for each displayed image as to whether to perform isolated point correction on the focus pixel 200 in the image. The weight setting UI 15 determines the values ​​of n and k in the above equation based on a combination of instructions input by the user for each image.

[0106] As described above, in this example, if one reference weight distribution is prepared, weight distributions having various characteristics can be generated by changing the value of n or the value of k.

[0107] <Threshold selection>

[0108] It is also possible to switch the image output unit 18 according to the dot gain. Figure 8 The threshold value used for comparison with the sum of the weights in step S20 of the sequence in the above. For example, the greater the dot gain of the image output unit 18, the smaller the value of the threshold value. For example, the threshold value is inversely proportional to the dot gain. The resolution conversion unit 16 maintains a rule, a relational expression, a table, etc. representing the relationship between such dot gain and the threshold value, and obtains a threshold value corresponding to the dot gain of the image output unit 18 based on the rule, etc., and uses it in S20. For example, when the image processing device 10 performs resolution conversion for an external printer, it obtains information on the dot gain of the printer from the printer via a network, etc., obtains a threshold value corresponding to the dot gain based on the rule, etc., and uses it in S20. Figure 8 etc. processing order.

[0109] Since the dots become larger as the dot gain increases, even the dots of the colored pixels farther away from the pixel of interest overlap with the dots of the pixel of interest. On the other hand, when the dots of the surrounding colored pixels overlap with the dots of the pixel of interest, the side that does not perform isolated dot correction has a better sense of graininess. Therefore, the larger the dot gain becomes, the more difficult it is to perform isolated dot correction, and the better the sense of graininess. Therefore, the larger the dot gain becomes in the image output unit 18 or the external printer, the more difficult it is to perform isolated dot correction, and therefore, the threshold used in S20 can be reduced.

[0110] The above-mentioned embodiments are merely illustrative, and various modifications can be made within the scope of the technical concept of the present invention. For example, the above-mentioned image processing device 10 binarizes the input multi-valued image data by error diffusion, but the binarization method is not limited to this. Of course, other methods such as dither method can also be used for binarization.

[0111] In addition, Figure 1 In the example of , the image processing device 10 has the image output unit 18, but it may also be a structure without the image output unit 18. In this case, the image processing device 10 may also receive an image printed by an external printer from the host, perform binarization and resolution conversion (including isolated point correction) on the image by the method of this embodiment, and supply the resulting image to the printer.

[0112] The information processing system 11 of the image processing device 10 described above is configured using, for example, a general-purpose computer. Fig.12 As shown, the computer 1000 includes a processor 1002, a memory (main storage device) 1004 such as a random access memory (RAM), a non-volatile storage device such as a flash memory or an SSD (solid state drive) or an HDD (hard disk drive), i.e., a controller for controlling an auxiliary storage device 1006, an interface with various input / output devices 1008, and a network interface 1010 for controlling connection with a network such as a local area network, and the like, and the like are connected via a data transmission path such as a bus 1012, for example. A program describing the contents of the processing of the above-mentioned embodiment is installed in the computer via a network, etc., and is stored in the auxiliary storage device 1006. The program stored in the auxiliary storage device 1006 is executed by the processor 1002 using the memory 1004, thereby constituting an information processing mechanism of the present embodiment. In addition, the information processing system 11 may also include an image processing processor, etc., for executing general-purpose or special-purpose image processing at high speed.

[0113] The information processing system 11 may be composed of a single computer or a plurality of computers. For example, a part of the functions of the information processing system 11 may be provided in another computer outside the image processing apparatus 10 .

[0114] In the above-mentioned embodiments, the processor refers to a processor in a broad sense, including a general-purpose processor (such as CPU: Central Processing Unit, etc.), a special-purpose processor (such as GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic devices, etc.).

[0115] In addition, the actions of the processors in the above-mentioned embodiments may not be performed by only one processor, but may be performed by cooperation of multiple processors in physically separated locations. In addition, the order of the actions of the processors is not limited to the order described in the above-mentioned embodiments, and may be appropriately changed.

[0116] (Note) (1)

[0118] An information processing system, wherein

[0119] With processor,

[0120] The processor

[0121] For each of the colored pixels around the colored pixel of interest in a predetermined area including the colored pixel of interest in the image data including white pixels and colored pixels, a weighting process is performed in which a smaller weight is assigned as the pixel is farther from the colored pixel of interest.

[0122] When the sum of the weights of the colored pixels around the pixel of interest is smaller than a threshold value, the pixel of interest is corrected. (2)

[0124] The information processing system according to (1) is characterized in that

[0125] The processor

[0126] Based on the value obtained by raising the base weight, which is a real value ranging from 0 to 1 and becomes smaller as it is farther from the pixel of interest, to the power of n (n is an integer greater than 1), the weight assigned to each of the colored pixels around the pixel of interest, which becomes smaller as it is farther from the pixel of interest, is calculated.

[0127] By changing the n, the degree of reduction of the weight can be changed according to the distance from the target pixel. (3)

[0129] The information processing system according to (1) or (2), characterized in that:

[0130] The processor

[0131] In a printing device that prints the image data corrected by the image processing device, for each color used for printing,

[0132] The assignment process is performed on image data including white pixels and colored pixels of the color,

[0133] Calculate the sum of the weights of the colored pixels around the pixel of interest.

[0134] In the case where the calculated sum of weights is less than a threshold value, if there are pixels in other colors whose sum of weights is greater than the threshold value, the pixel of interest is not corrected; and if there are no pixels in other colors whose sum of weights is greater than the threshold value, the pixel of interest is corrected. (4)

[0136] The information processing system according to any one of (1) to (3), wherein the processor

[0137] As the threshold value, a value which becomes smaller as the dot gain of a printing device which prints the image data corrected by the image processing device increases is used. (5)

[0139] A program for

[0140] The computer is made to execute the following processing:

[0141] For each of the colored pixels around the colored pixel of interest in a predetermined area including the colored pixel of interest in the image data including white pixels and colored pixels, a weighting process is performed in which a smaller weight is assigned as the pixel is farther from the colored pixel of interest.

[0142] When the sum of the weights of the colored pixels around the pixel of interest is smaller than a threshold value, the pixel of interest is corrected.

[0143] According to the information processing system described in (1) and the program described in (5), an output image with good graininess can be obtained compared to a method of controlling whether to correct the focus pixel based on the number or ratio of colored pixels in a predetermined area including the focus pixel.

[0144] According to the information processing system described in (2), it is possible to adjust the degree of reduction of the weight according to the distance from the target pixel.

[0145] According to the information processing system described in (3), when processing a multi-color image, it is possible to reduce changes in color balance due to correction compared to a method that considers only colored pixels of an image of a color to which the pixel of interest belongs.

[0146] According to the information processing system described in (4), compared with the case where the same threshold is used regardless of the dot gain of the printing device, an output image with better graininess can be obtained.

Claims

1. An information processing system, characterized in that: With processor, The processor For each of the colored pixels around the focused pixel in a predetermined area including a focused colored pixel in image data containing white pixels and colored pixels, a weighting process is performed in which a smaller weight is assigned to each pixel farther from the focused pixel. When the sum of the weights of the colored pixels around the pixel of interest is smaller than a threshold value, the pixel of interest is corrected.

2. The information processing system according to claim 1, wherein: The processor Based on the value obtained by raising the base weight, which is a real value ranging from 0 to 1 and becomes smaller as it is farther from the pixel of interest, to the power of n (n is an integer greater than 1), the weight assigned to each of the colored pixels around the pixel of interest, which becomes smaller as it is farther from the pixel of interest, is calculated. By changing the n, the degree of reduction of the weight can be changed according to the distance from the target pixel.

3. The information processing system according to claim 1 or 2, wherein: The processor In a printing device that prints the image data corrected by the image processing device, for each color used for printing, performing the assignment process on image data including white pixels and colored pixels of the color, Calculate the sum of the weights of the colored pixels around the pixel of interest. In the case where the calculated sum of weights is less than a threshold value, if there are pixels in other colors whose sum of weights is greater than the threshold value, the pixel of interest is not corrected; and if there are no pixels in other colors whose sum of weights is greater than the threshold value, the pixel of interest is corrected.

4. The information processing system according to any one of claims 1 to 3, wherein: The processor As the threshold value, a value which becomes smaller as the dot gain of a printing device which prints the image data corrected by the image processing device increases is used.

5. A computer-readable medium storing a program for causing a computer to execute a process, characterized in that: The processing For each of the colored pixels around the focused pixel in a predetermined area including a focused colored pixel in image data containing white pixels and colored pixels, a weighting process is performed in which a smaller weight is assigned to each pixel farther from the focused pixel. When the sum of the weights of the colored pixels around the pixel of interest is smaller than a threshold value, the pixel of interest is corrected.

6. An information processing method, characterized in that: For each of the colored pixels around the focused pixel in a predetermined area including a focused colored pixel in image data containing white pixels and colored pixels, a weighting process is performed in which a smaller weight is assigned to each pixel farther from the focused pixel. When the sum of the weights of the colored pixels around the pixel of interest is smaller than a threshold value, the pixel of interest is corrected.

Images