JP2015149545A - Image processing apparatus, control method of the same, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a light grey character from being surrounded by black.SOLUTION: When the number of black pixels darker than a threshold in a reference region is counted and when it is larger than a predetermined value, it is determined that a target pixel is to be converted to a K monochrome.

Description

  The present invention relates to edge color determination.

  When a black object is color-scanned, pixels satisfying the relationship “maximum RGB value−minimum value” ≠ 0 are generated at the edge pixels of the black object. Such a phenomenon is called color shift. This color shift occurs because the positions of the R sensor, the G sensor, and the B sensor in the color scanner are slightly shifted from each other.

  Therefore, in the color scanner, a threshold value is provided, and when “the maximum value of RGB values−the minimum value” <the threshold value, the edge pixel is determined to be an achromatic color. Then, the edge pixel determined to be an achromatic color is converted into CMYK (K ≠ 0, C = M = Y = 0, hereinafter such CMYK is referred to as K single color), and the edge pixel determined to be a chromatic color. Is converted to CMYK (C ≠ 0, M ≠ 0, Y ≠ 0, K may be 0 or not 0. Such CMYK is hereinafter referred to as four colors). By performing such processing, the edge pixel of the black object is printed in K single color (Patent Document 1).

Japanese Patent No. 3944032

  However, when this method is applied to a gray (light black) object (901 in FIG. 9), the inside of the object is printed in four colors, but the edge pixel is printed in K single color. (902 in FIG. 9). In other words, a picture appears that surrounds a gray object in black.

  An image processing apparatus that solves the above-described problem includes means for determining whether the color of each pixel included in the input image is a chromatic color or an achromatic color, and the color of each pixel included in the input image is a first color. Means for determining whether it is darker than a threshold, and having a color determined to be achromatic and present in a reference region surrounding the pixel of interest in the input image and to be darker than the first threshold Means for determining the number of pixels, and when it is determined that the color of the target pixel is an achromatic color and the determined number of pixels is greater than a second threshold value, It has the conversion means which converts a color into K single color, It is characterized by the above-mentioned.

  The number of occurrences of a picture surrounding a gray object in black is reduced.

2 is a diagram illustrating a software configuration of the image forming apparatus 101. FIG. 2 is a block diagram showing a configuration within an image processing unit 102. FIG. It is the figure which showed the black character. It is the figure which showed the gray character. 6 is a flowchart of processing of an achromatic color determination processing unit 203 according to the first embodiment. 10 is a flowchart of processing of an achromatic color determination processing unit 203 according to Embodiment 2. 5 is a flowchart of a color conversion processing unit 204. 10 is a flowchart of processing of an achromatic color determination processing unit 203 according to Embodiment 3. Illustration explaining the problem The figure explaining the view of Embodiment 1

The concept of Embodiment 1 will be described first with reference to FIG. In FIG. 10, the center hatched pixel is the target pixel. In the case of 1001, the case of 1002, and the case of 1003, the pixel of interest is an edge pixel that has been determined to be achromatic. First, in the conventional technique, the edge pixel that has been determined to be achromatic is K. Convert to a single color. On the other hand, in the first embodiment, when the edge pixel determined to be achromatic is 1001 or 1002, it is converted to K single color. On the other hand, in the case of 1003, it is converted into four colors. This idea is as follows.

  Usually, there are more dark achromatic pixels than the threshold (for example, the threshold is 2) around the edge pixels of black characters. For example, there are 6 pixels as 1001 and 3 pixels as 1002. In such a case, the pixel of interest should be converted to K monochrome.

  On the other hand, dark achromatic pixels are below the threshold value around the edge pixels of light black characters. For example, in the case of 1003, the dark achromatic pixel is zero. In such a case, the pixel of interest should be converted to four colors. This is for avoiding that the frame of the thin black character is surrounded by black as shown in FIG.

(Embodiment 1)
First, a configuration example of software will be described.

<< Example of Software Configuration-Image Forming Apparatus >>
FIG. 1 is a diagram for explaining the configuration of the image forming apparatus 100. The image forming apparatus 100 includes an image input unit 101, an image processing unit 102, and an image output unit 103. Hereinafter, each part will be described.

  First, the image input unit 101 is a scanner, for example. The image input unit 101 inputs RGB images to the image processing unit 102. Next, the image processing unit 102 performs various image processes on the input RGB image (input image). Details of the image processing unit 102 will be described later. The image output unit 103 is, for example, a CMYK printer engine, and prints an image received from the image processing unit 102.

  Next, the configuration in the image processing unit 102 will be described with reference to FIG.

  First, the MTF processing unit 201 corrects the MTF for main scanning and sub-scanning by performing MTF processing on the input image. The corrected image is input to the image area determination unit 202 and the achromatic color determination processing unit 203.

  The image area determination unit 202 pays attention to each pixel and determines whether the pixel of interest is an edge pixel of a character or the other. Since the image area determination technique is a known technique, the details thereof are omitted. If the threshold is less than or equal to 2, the continuous black pixels are determined to be characters. A technique for determining the outline of the determined character as an edge portion of the character is known.

  Thereafter, the achromatic color determination processing unit 203 determines whether the pixel determined to be the edge portion of the character should be converted to K single color or four colors. Details of the achromatic color determination processing unit 203 will be described later.

  Thereafter, the color conversion processing unit 204 converts the pixel determined to be the edge portion of the character and to be converted to K single color from RGB to K single color, and the other pixels from RGB to four colors. Convert.

  Next, the filter processing unit 205 performs edge enhancement on the edge portion of the character and performs smoothing (smoothing = blurring processing) on the other portions. Thereby, while the edge part of a character can be clarified, the other part can be smoothed.

  Then, the gamma processing unit 206 converts the gradation according to the density characteristic at the time of output of the image forming apparatus 100 (that is, performs gamma correction), and finally the dither processing unit 207 performs dither processing, and the image output unit 103 Send to.

  Next, the achromatic color determination processing unit 203 will be described. The achromatic color determination processing unit 203 determines that the edge portion of a black character should be converted to K single color. On the other hand, it is determined that the edge portion of the gray character should be converted into four meals. Black characters will be described with reference to FIG. 3, and gray characters will be described with reference to FIG.

  FIG. 3B is an enlarged view of a part 301 of FIG. 3A showing black characters. A target pixel 302 to be processed and a reference area 303 that refers to the periphery of the target pixel 302 are shown. The reference area 303 may be a 3 × 3 pixel area centered on the target pixel, or may be an area of 5 × 5 pixels or more. In this embodiment, the reference area 303 will be described below as an area of 3 × 3 pixels. The reference area 303 may or may not include the pixel of interest, but will be described below as not being included. That is, the reference area is 8 pixels excluding the target pixel in the 3 × 3 pixel area.

  A gray portion 305 indicates a portion where the edge is blurred and thinned when the scanner reads black characters. Reference numeral 304 denotes a pixel corresponding to the inside of a black character, and is not thinned. Further, the number 306 is determined as the edge of the character by the image area determination unit 202. 3B, 3C, and 3D can be considered depending on the position of the pixel of interest 302.

  That is, in FIG. 3B, the target pixel 302 and all the pixels in the reference area 303 are pixels belonging to the black character portion 304. In FIG. 3C, the target pixel 302 belongs to the black character portion 304, but some pixels in the reference area 303 belong to the gray portion 305. Finally, in FIG. 3D, the target pixel 302 belongs to the gray portion 305, but there are pixels belonging to the black character portion 304 in the reference area 303.

  According to the present embodiment, for a black character, the achromatic color determination processing unit 203 converts the pixel of interest 302 into K single color in any of the cases of FIG. 3B, FIG. 3C, and FIG. Judge that it should be.

  On the other hand, FIG. 4B is an enlarged view of a part 401 of FIG. 4A showing gray characters, and shows a target pixel 402 to be processed and a reference region 403 that refers to the surrounding area. Yes. A light gray portion 405 indicates a portion where the edge is blurred and thinned when the scanner reads gray characters. Further, the number 406 is determined as the edge of the character by the image area determination unit 202. 4B, 4C, and 4D can be considered depending on the position of the pixel of interest 402.

  That is, in FIG. 4B, the target pixel 402 and all the pixels in the reference area 403 belong to the gray character portion 404. In FIG. 4C, the target pixel 402 belongs to the gray character portion 404, but there are pixels belonging to the light gray portion 405 in the reference area 403. Finally, in FIG. 4D, the pixel of interest belongs to the light gray portion 405, and there are also pixels belonging to the gray portion 404 in the reference region 403.

  According to the present embodiment, the achromatic color determination processing unit 203 sets the target pixel 402 to four colors in any of FIGS. 4B, 4C, and 4D for gray characters. Judge that it should be converted.

  Hereinafter, the achromatic color determination processing unit 203 determines the achromatic color in the case of FIGS. 3B, 3 </ b> C, and 3 </ b> D using the flowchart of FIG. 5, and FIG. In the case of FIGS. 4C and 4D, a method for determining a chromatic color will be described.

  First, in Step 1a, it is determined whether or not the target pixel is an achromatic color. Here, color space conversion from RGB color space to Lab is performed, and whether or not the color is achromatic is determined depending on which region in the Lab space is located. For example, it is determined that a pixel having a color difference value smaller than the threshold value (a value and b value is small) is an achromatic color. As a result, if it is a chromatic color, it will become No and will progress to Step10a, and if it is an achromatic color, it will become Yes and will progress to Step2a.

  Next, in Step 2a, each pixel present in the reference area is picked up, and it is determined whether or not the pixel is an achromatic color. If it is a chromatic color, it will progress to Step 5a, and if it is an achromatic color, it will progress to Step 3a. In Step 3a, it is determined whether or not the pixels in the reference area are dark pixels. Here, it is determined whether or not the value of L is a pixel whose value is darker than the threshold value. If it is determined that the pixel is a thin pixel (a pixel having an L value equal to or greater than the threshold value), the process proceeds to Step 5a. If it is determined that the pixel is a dark pixel, the process proceeds to Step 4a. In Step 4a, the number of pixels determined to be achromatic and dark is counted. Thereafter, in Step 5a, it is determined whether or not all the pixels in the reference area have been determined. When all the pixels in the reference area have been determined, the determination becomes Yes, and the process proceeds to Step 7a. If No, the process proceeds to Step 6a. In Step 6a, the process proceeds to the next pixel in the next reference area and proceeds to Step 2a. With the above processing, the number of pixels darker than the achromatic threshold existing in the reference area is counted.

  Thereafter, in Step 7a, it is determined whether or not the number of pixels darker than the achromatic threshold value in the reference area is greater than a predetermined number (threshold value). When there are many, it progresses to Step8a, but when there are few, it progresses to Step9a. In Step 8a, it is determined that the color is to be converted to K single color, and the process is ended. On the other hand, in Step 9a, it is determined that the color is to be converted to four colors, and the process is ended.

  If it is determined that the color is chromatic in Step 1a, the process proceeds to Step 10a, and it is determined whether or not the pixels in the reference area are achromatic in Step 10a. If it is determined that the color is chromatic, the process proceeds to Step 12a. If it is determined that the color is achromatic, the process proceeds to Step 11a. In Step 11a, achromatic pixels are counted, and in Step 12a, it is determined whether all the pixels in the reference area have been determined. Here, if all the pixels in the reference area have not been determined, the result is No and the process proceeds to Step 13a. In Step 13a, the process proceeds to the next pixel in the reference area, and then proceeds to Step 10a. On the other hand, if all the pixels in the reference area are determined in Step 12a, the process proceeds to Step 14a, where it is determined whether or not the number of pixels determined to be achromatic in Step 14a is greater than a predetermined threshold B. If it is determined that the number is large, the process proceeds to Step 15a, where it is determined that the color should be converted to K single color, and the process ends.

  Here, in Step 1a, in the determination method from Step 10a to Step 16a when the target pixel is a chromatic color, whether the target pixel is a chromatic color or an achromatic color is determined based on the number of achromatic pixels in the reference region. However, the Lab of all the pixels in the target pixel and the reference region may be averaged to determine whether the average Lab is located in the achromatic region or the chromatic region in the Lab space. . Note that the reason why the processing changes depending on whether the target pixel is achromatic or chromatic in Step 1a is that when the target pixel is chromatic, the number of dark pixels in the reference area is not relevant. . For example, if the background of a black character is a red background and the pixel of interest is on the red background and there is a black pixel of a black character in the reference area, it should be determined as a chromatic color. However, there may be a case where the target pixel is erroneously determined to be a chromatic color, and it is necessary to save such a case. Therefore, in this embodiment, when there are a large number of pixels that are achromatic colors other than the target pixel, it is considered that the target pixel was actually originally an achromatic color, and it is determined that it should be converted to K single color. ing.

  The detailed description of the achromatic color determination processing unit 203 ends here. The achromatic color determination processing unit 203 performs the achromatic color determination process (the process of FIG. 7) only on the pixels determined by the image area determination unit 202 as the edge portion of the character. The achromatic color determination process (the process of FIG. 7) is not performed for the other pixels.

  According to the above description, the achromatic color determination processing unit 203 determines an achromatic color if the pixel of interest is an achromatic color and the number of dark pixels in the reference area is greater than the threshold A, but the pixel of interest is determined to be an achromatic color. If the dark pixel in the reference area is equal to or less than the threshold A, it means that the pixel is determined as a chromatic color.

  Accordingly, the black character is converted to K monochrome because there are more dark pixels in the reference area 303 than the threshold A (= 2) in any of the cases of FIGS. 3B, 3C, and 3D. It is determined that it should be. On the other hand, the gray characters are determined to be converted into four colors because dark pixels in the reference area 403 are less than the threshold value A in any of the cases of FIGS. 4B, 4C, and 4D. The

  As described above, the edge portion of the black character is determined as an achromatic color and is output in K single color, while the edge portion of the gray character is determined as a chromatic color and is output in four colors. As a result, it is possible to prevent image deterioration in which the edge of a gray character is surrounded by a single K color, while an output with good readability can be provided by outputting the black character edge in a single K color.

(Embodiment 2)
In the first embodiment, in Step 7a of the achromatic color determination processing unit 203, it is determined whether or not the color is an achromatic color depending on whether the number of black pixels in the reference area is larger or smaller than a predetermined threshold value. As a result, there is a possibility that the pixel output in the K single color and the pixel output in the four colors are switched depending on whether the number is larger or smaller than the predetermined number.

  Therefore, in the second embodiment, a plurality of threshold values are prepared in advance when counting black pixels in the reference area, and the amount of K when outputting in four colors is adjusted according to the number of black pixels in the reference area. Hereinafter, this will be described with reference to the flowchart of FIG. Note that the description of the contents described in the first embodiment is omitted.

  Since Step 1a to Step 6a are the same as those in the first embodiment, description thereof is omitted. In Step 7a, if the number of dark pixels counted in Step 4a is compared with the predetermined threshold A, the result is No, and the process proceeds to Step 9a, where it is determined that the four colors should be converted. On the other hand, if it is larger than the threshold A, it becomes Yes and proceeds to Step 1b. In Step 1b, if the number of dark achromatic pixels counted in Step 4a is smaller than the predetermined threshold C, the result is No and the process proceeds to Step 2b and is determined to be gray. If there are more, the result is Yes, and the process proceeds to Step 8a, where it is determined that the color should be converted to K single color. Here, the relationship of threshold A <threshold C is established.

  Since Step 9a to Step 16a are the same as those in the first embodiment, description thereof is omitted. This is the end of the description of the flowchart of FIG. Similar to the first embodiment, the above processing is also performed only on the edges of characters and objects.

Next, the color conversion processing unit 204 will be described with reference to the flowchart of FIG.
In Step 1c, it is determined whether it is determined that the pixel of interest should be converted into four colors. If the pixel is determined to be four colors, the result is Yes, the process proceeds to Step 2c, and RGB is converted to four colors, and the process ends. If the pixel is not determined to be four colors, the result is No and the process proceeds to Step 3c. In Step 3c, it is determined whether or not it is determined as a gray pixel. If the pixel is determined to be a gray pixel, the result is Yes, and the process proceeds to Step 4c to convert RGB to C′M′Y′K ′. Here, C′M′Y′K ′ has a relationship of C ′ <C, M ′ <M, Y ′ <Y, K ′> K as compared with CMYK in Step 2c. If the pixel is not determined to be a gray pixel, the result is No and the process proceeds to Step 5c, where RGB is converted to K single color. This is the end of the description of the color conversion processing unit 204.

  The amount of K can be controlled by determining the color to be K single color, gray pixel, or four colors according to the number of black pixels in the reference area by the above processing. As a result, even if the number of pixels determined to be black pixels is near the threshold value, the amount of K does not fluctuate drastically, so that deterioration in image quality can be prevented. In the present embodiment, the determination is made to be K single color, gray, or four colors according to the number of black pixels in the reference area. However, the amount of CMYK when the color conversion processing unit 204 converts from RGB to CMYK may be changed more finely by determining more finely as K single color, gray 1, gray 2... Four colors.

(Embodiment 3)
In the second embodiment, a plurality of thresholds for counting black pixels in the reference area are provided, thereby making the switching between pixels output in K single color and pixels output in four colors inconspicuous. In the third embodiment, by having a plurality of threshold values based on the darkness of the black pixels in the reference area, switching between pixels that are output in K single color and pixels that are output in four colors is made inconspicuous. Hereinafter, a description will be given with reference to the flowchart of FIG. In this embodiment, the description of the contents described in the other embodiments is omitted. Since Step 1a to Step 2a are the same as those in the first embodiment, description thereof will be omitted.

  In Step 1d, it is determined whether or not the pixels in the reference area are darker than a predetermined threshold value D. Here, if the L value of the pixel is low, it is determined that the pixel is dark. As a result, if the pixel is thin, the result is No and the process proceeds to Step 3d. If the pixel is dark, the process proceeds to Yes. In Step 2d, the number of pixels is counted and the process proceeds to Step 5a.

  On the other hand, in Step 3d, it is determined whether or not the pixels in the reference area are darker than a predetermined threshold value E. If it is light here, it becomes No and proceeds to Step 5a, and if it is dark, it becomes Yes and proceeds to Step 4d. In Step 4d, the number of pixels is counted and the process proceeds to Step 5a. Since Step 6a is the same as that of the first embodiment, it is omitted.

  In Step 5d, it is determined whether or not there are more pixels darker than the threshold value D than a predetermined threshold value F. If there is more, it will become Yes and will progress to Step8a, and it will determine that it should convert into K single color, and if it is less, it will become No and will progress to Step6d. In Step 6d, it is determined whether or not the total number of pixels determined to be darker than the threshold E and pixels determined to be darker than the threshold D is greater than a predetermined threshold G. If there is more, it becomes Yes and proceeds to Step 2b and is determined to be gray, and if it is less, it becomes No and proceeds to Step 9a to determine that it should be converted into four colors. Step 10a to Step 16a are the same as those in the first embodiment, and are omitted.

  This is the end of the description of the flowchart of FIG. Here, the threshold E is determined to be a pixel thinner than the threshold D. By doing so, in the first embodiment, the determination of whether it is an achromatic color or a chromatic color may change in one determination of Step 3a. However, in this embodiment, the determination of No in Step 1d can be determined as Yes in Step 3d. .

  Since the color conversion processing unit 204 is the same as the method of the second embodiment, the description thereof is omitted. With the above processing, when counting pixels with dark reference pixels, it is possible to prevent the determination of whether the color is K single color or four colors depending on the threshold value. As a result, by having a plurality of threshold values based on the darkness of the black pixels in the reference area, it is possible to make the switching between pixels that are output in K single color and pixels that are output in four colors inconspicuous.

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

  In each of the above embodiments, in step 1a, step 2a, step 3a, step 10a, step 1d, and step 3d, the determination 1 of whether the color of each pixel is an achromatic color or a chromatic color, and the color of each pixel is darker than the threshold value Whether or not to determine 2 is made. However, instead of performing these determinations in each step, determination 1 and determination 2 are performed for all pixels in one page in advance, and in each step, the determination result of determination 1 or determination 2 is referred to. Anyway. In that case, the determination 1 and the determination 2 are performed before the achromatic color determination processing unit 203 performs the processing shown in the flowchart of FIG. 5, FIG. 6, or FIG.

  In each of the above embodiments, even if it is determined that the color of the pixel of interest is a chromatic color, if it is determined that there are achromatic pixels or more in the reference region, the color of the pixel of interest is changed. It is determined that it should be converted to K monochrome (step 14a). However, it is not necessary to determine whether or not an achromatic color pixel is present in the reference region at or above the threshold (hereinafter referred to as determination A). That is, without performing this determination A, when it is determined that the color of the pixel of interest is a chromatic color, it may be determined that the color of the pixel of interest should be converted into four colors.

  Note that the reason why the determination A is performed in each of the above embodiments is that even if the pixel of interest has a chromatic color, it may be wrong. For example, when it is determined that the color of the target pixel is a chromatic color and all the colors of other pixels (for example, eight pixels) in the reference region are achromatic colors, the color of the target pixel is actually an achromatic color. (Just because it was determined to be chromatic due to color shift). In order to save such a case, the determination A is performed in each embodiment.

  However, even when this determination A is performed, the determination criterion (threshold value) must be large. When it is determined that the color of the target pixel is a chromatic color, it should not be determined that it should be easily converted to K single color, compared to when it is determined that the color of the target pixel is an achromatic color. . Therefore, the threshold value (threshold value B) used in step 14a should be 1 or more (preferably 2 or more) larger than the threshold value (threshold value A) used in step 7a. Further, the threshold value (threshold value 2) used in step 14a should be 1 or more (preferably 2 or more) larger than the threshold value (threshold value F) used in step 5d.

101 Image input unit 102 Image processing unit 103 Image output unit

Claims (17)

Means for determining whether the color of each pixel included in the input image is a chromatic color or an achromatic color;
Means for determining whether the color of each pixel included in the input image is darker than a first threshold;
Means for determining the number of pixels that exist in a reference region surrounding the target pixel in the input image, are determined to be achromatic, and have a color determined to be darker than the first threshold;
Conversion means for converting the color of the pixel of interest into a K single color when it is determined that the color of the pixel of interest is an achromatic color and the number of determined pixels is greater than a second threshold value An image processing apparatus comprising: The converting means includes
When it is determined that the color of the pixel of interest is an achromatic color and the number of determined pixels is less than a second threshold, the color of the pixel of interest is converted into four colors of CMYK. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the reference area is a 3 × 3 pixel area centered on the target pixel.   The image processing apparatus according to claim 3, wherein the target pixel is not included in the reference area. The color of the pixel of interest is represented in RGB before conversion,
K single color is CMYK (K ≠ 0, C = M = Y = 0),
The image processing apparatus according to claim 2, wherein the four colors are CMYK (C ≠ 0, M ≠ 0, Y ≠ 0, K may be 0 or not 0). To determine whether the color of each pixel included in the input image is chromatic or achromatic,
The image processing apparatus according to claim 1, wherein the image processing apparatus performs the comparison by comparing a color difference between the colors of the pixels and a third threshold value.   The image processing apparatus according to claim 1, wherein the target pixel is an edge pixel.   The image processing apparatus according to claim 1, wherein the target pixel is an edge pixel of a character. Determining whether the color of each pixel included in the input image is a chromatic color or an achromatic color;
Determining whether the color of each pixel included in the input image is darker than a first threshold;
Determining the number of pixels present in a reference region surrounding the target pixel in the input image, determined to be achromatic, and having a color determined to be darker than the first threshold;
A conversion step of converting the color of the pixel of interest into a K single color when it is determined that the color of the pixel of interest is an achromatic color and the number of determined pixels is greater than a second threshold value. A control method for an image processing apparatus, comprising: The conversion step includes
When it is determined that the color of the pixel of interest is an achromatic color and the number of determined pixels is less than a second threshold, the color of the pixel of interest is converted into four colors of CMYK. The method of controlling an image processing apparatus according to claim 9.   11. The method according to claim 9, wherein the reference area is a 3 × 3 pixel area centered on the target pixel.   The method according to claim 11, wherein the target pixel is not included in the reference region. The color of the pixel of interest is represented in RGB before conversion,
K single color is CMYK (K ≠ 0, C = M = Y = 0),
11. The method of controlling an image processing apparatus according to claim 10, wherein the four colors are CMYK (C ≠ 0, M ≠ 0, Y ≠ 0, K may be 0 or not 0). To determine whether the color of each pixel included in the input image is chromatic or achromatic,
The method of controlling an image processing apparatus according to any one of claims 9 to 13, wherein the control is performed by comparing a color difference between the colors of the pixels and a third threshold value.   The method according to claim 9, wherein the target pixel is an edge pixel.   The method of controlling an image processing apparatus according to claim 9, wherein the target pixel is an edge pixel of a character.   A program for causing a computer to execute the control method according to any one of claims 9 to 16.

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