JP5854210B2 - Image processing apparatus and image processing program - Google Patents

Description

  The present invention relates to an image processing apparatus and an image processing program.

  As image processing, processing such as limiting the number of colors used in an image to some representative colors and converting the used colors into representative colors to generate a limited color image is performed. For example, in Patent Document 1, a representative color is selected from a given image, and the color of each pixel in the image is replaced with the representative color to obtain a limited color image.

  For example, consider a case where a limited color image is generated from an image obtained by optically reading a wrinkled document. When the document is wrinkled, the way the light strikes varies depending on the location, so that a color change (for example, density change) occurs due to wrinkles in the optically read image. For this reason, in the limited color image, the representative color to be converted may differ depending on the density.

  For example, there is a case where an area of a certain color has a light reflection that is stronger than the other areas due to wrinkles of the document and becomes lighter than the color of an area not affected by other wrinkles. In such a case, the area may be converted to a representative color different from other areas. In this case, not only the background but also the foreground such as characters and figures drawn on the background are lighter than other areas. Therefore, depending on the converted representative color, the color difference between the foreground and the background may be smaller than in other regions, or the foreground color may be converted into the background representative color and disappear.

  Conversely, wrinkles can cause darker areas than the original color. In this case, in the darkened area, the background and foreground are darker than the colors of the other areas, and may be converted to a representative color different from the other areas. Also in this case, depending on the converted representative color, the color difference between the foreground and the background may be smaller than in other regions, or the foreground color may be converted into the background representative color and disappear.

  Such a phenomenon occurs not only in the wrinkle of the original but also in the case where the background density of a blue-printed original or the like is uneven, or in the case where the density of handwritten characters is not uniform. In these cases as well, if an image obtained by reading an original with an image reading device is converted into a limited color image, it is converted into an unintended representative color, and the color difference between the foreground and the background becomes smaller or disappears than other areas. May end up.

  Unlike the above-mentioned phenomenon, when the thin line of the character on the document is optically read, the character and background colors are mixed at the boundary between the character and the background, resulting in different colors. In Patent Document 2, in such a case, the character portion is extracted, the average color of the character portion is calculated, and the character color is determined according to the internal ratio obtained from the number of boundary pixels with the background of the character portion and the number of internal pixels. The character color is corrected so that the difference between the background color and the background color is larger than the average color, and is used as the representative color of the character area. In Patent Document 3, a color image is divided into blocks, an average color and a representative color are extracted for each block, an average color of non-boundary blocks is set as a background color, and a boundary block is determined based on the representative color. In the block determined as the boundary, a representative color other than the background color is selected and encoded, and processing is performed so that the boundary is identified for the boundary portion where the color turbidity exists.

JP 2008-0665803 A JP 2009-17247 A JP-A-1-157185

  An object of the present invention is to provide an image processing apparatus and an image processing program capable of generating a limited color image in which the foreground and background are clearly reproduced.

  According to the first aspect of the present invention, an extraction unit that extracts a representative color from a processing target image and a processing region having a predetermined size including a target pixel in the processing target image are separated into a foreground region and a background region. Separating means for calculating the color difference between the color of the foreground area and the color of the background area, and when the color difference calculated by the calculation means is smaller than a predetermined value, Corresponding to the modified representative color or the background area corresponding to the foreground area that increases the color difference from the representative colors extracted by the extracting means according to the distance from the straight line passing through the corresponding representative color and the representative color corresponding to the background area An image processing apparatus comprising: selection means for selecting a corrected representative color to be replaced; and replacement means for replacing the color of the target pixel with the corrected representative color selected by the selection means.

  The invention according to claim 2 of the present application separates a foreground area and a background area from an extraction means for extracting a representative color from a processing target image, and a processing area of a predetermined size including a target pixel in the processing target image. Separating means for calculating the color difference between the color of the foreground area and the color of the background area, and when the color difference calculated by the calculation means is smaller than a predetermined value, A corrected representative color corresponding to the foreground area or a corrected representative color corresponding to the background area that increases the color difference from the representative colors extracted by the extraction means according to the distance from the straight line passing through the average color and the average color of the background area An image processing apparatus comprising: a selecting unit that selects the color of the target pixel with a corrected representative color selected by the selecting unit.

  According to a third aspect of the present invention, the selecting means according to the second aspect of the invention corresponds to the foreground area corresponding to a straight line passing through an average color of the foreground area and an average color of the background area in a color space. When the angle formed by a straight line passing through the representative color corresponding to the background region and the representative color corresponding to the background region is larger than a predetermined angle, the corrected representative color is selected regardless of the color difference calculated by the calculating means. The image processing apparatus.

  The invention according to claim 4 of the present application separates an extraction means for extracting a representative color from the processing target image, and a processing area having a predetermined size including the target pixel in the processing target image into a foreground area and a background area. Separating means for calculating the color difference between the foreground area color and the background area color, and the representative extracted by the extraction means when the color difference calculated by the calculation means is smaller than a predetermined value. For each of the two representative color sets obtained from the color, a color difference between one of the representative colors of the set and the color of the foreground area and a color difference between the other of the representative colors and the color of the background area are obtained as errors, and the error In addition, a value of an evaluation function using the color difference between two representative colors is obtained, a set of representative colors is obtained from the value of the evaluation function, and the foreground region in which the color difference is increased from the representative colors extracted by the extraction unit. Corresponding correction fee An image processing apparatus comprising: selection means for selecting a corrected representative color corresponding to a color and the background area; and replacement means for replacing the color of the target pixel with the corrected representative color selected by the selection means. .

  In the invention according to claim 5 of the present application, when the selection representative color in the invention according to any one of claims 1 to 4 does not include the corrected representative color that satisfies a predetermined condition, A representative color in which a color difference between a representative color corresponding to the background area and a representative color corresponding to the background area is larger than a predetermined value on a straight line passing through the color of the foreground area and the color of the background area in a color space; The image processing apparatus is characterized in that a representative color having a color difference larger than a predetermined value is added and selected as the corrected representative color.

  The invention according to claim 6 of the present application uses the representative color corresponding to the foreground region as the color of the foreground region by the calculation means according to any one of claims 1 to 5 of the present application, An image processing apparatus that calculates a color difference using a representative color corresponding to the background area as a color of the background area.

  In the invention according to claim 7 of the present application, the calculation means in the invention according to any one of claims 1 to 5 is characterized in that an average color of each pixel in the foreground area or each color as the color of the foreground area A color difference is calculated using an average color of representative colors corresponding to pixels and using an average color of each pixel in the background area or an average color of representative colors corresponding to each pixel as the color of the background area. An image processing apparatus.

  According to an eighth aspect of the present invention, in addition to the configuration of the first aspect of the present invention, a contour determination unit that determines whether or not the pixel of interest is a contour region. And the replacement means replaces the target pixel determined to be a contour region by the contour determination means.

  The invention according to claim 9 of the present application further includes color number determination means for determining the number of colors of the processing region in the configuration of the invention according to any one of claims 1 to 8 of the present application, The replacement unit is an image processing apparatus that does not perform replacement on a target pixel that has been determined by the color number determination unit to have a color number of 3 or more.

  The invention according to claim 10 of the present application further includes color number determination means for determining the number of colors of the processing region in the configuration of the invention according to any one of claims 1 to 8 of the present application, The separation unit changes the size of the processing region to be smaller than the current size when the number of colors is determined to be 3 or more by the color number determination unit, and separates the foreground region and the background region. An image processing apparatus characterized by performing the processing.

  The invention described in claim 11 is an image processing program for causing a computer to execute the function of the image processing apparatus described in any one of claims 1 to 10.

  According to the first aspect of the present invention, the representative color can be changed while maintaining the tendency of the foreground and background colors, and the foreground and the background are clearly reproduced as compared with the case without this configuration. A limited color image can be generated.

  According to the second aspect of the present invention, the representative color can be changed while maintaining the tendency of the foreground and background colors in the processing target image, and the foreground and background are clear as compared with the case where the present configuration is not provided. The limited color image reproduced in the above can be generated.

  According to the third aspect of the present invention, selection of a representative color different from the colors used for the foreground and the background in the processing target image can be prevented.

  According to the invention described in claim 4 of the present application, it is possible to select the optimum representative color and generate a limited color image in which the foreground and the background are clearly reproduced as compared with the case without this configuration.

  According to the fifth aspect of the present invention, it is possible to generate a limited color image in which the foreground and the background are clearly reproduced even when there is no representative color to be selected among the extracted representative colors.

  According to the sixth aspect of the present invention, the representative color can be changed according to the color difference in the limited color image.

  According to the seventh aspect of the present invention, an appropriate color difference can be calculated even when the foreground region and the background region have non-uniform colors.

  According to the invention described in claim 8 of the present application, it is possible to generate a limited color image in which the foreground and background in the contour are clearly reproduced as compared with the case where the present configuration is not provided.

  According to the ninth aspect of the present invention, it is possible to prevent an undesired change in the representative color due to the influence of a plurality of colors.

  According to the invention described in claim 10 of the present application, it is possible to prevent an undesired change in representative color due to the influence of a plurality of colors.

  According to the invention of claim 11 of the present application, the effect of the invention of any one of claims 1 to 10 can be obtained.

It is a block diagram which shows one Embodiment of this invention. It is a flowchart which shows an example of the operation | movement in one Embodiment of this invention. It is explanatory drawing of the 1st example of the selection process of a correction representative color. It is explanatory drawing of an example of the selection range in the 1st example of the selection process of a correction representative color. It is explanatory drawing of an example of the addition process of a representative color. It is explanatory drawing of the 2nd example of the selection process of a correction representative color. It is explanatory drawing of the 3rd example of the selection process of a correction representative color. It is explanatory drawing of an example of the selection range in the 3rd example of the selection process of a correction representative color. It is explanatory drawing of another example of the addition process of a representative color. It is explanatory drawing of the 4th example of the selection process of a correction representative color. It is a block diagram which shows the modification in one Embodiment of this invention. It is a flowchart which shows an example of the operation | movement in the modification of one Embodiment of this invention. FIG. 16 is an explanatory diagram of an example of a computer program, a storage medium storing the computer program, and a computer when the functions described in the embodiment of the present invention and the modifications thereof are realized by a computer program.

  FIG. 1 is a configuration diagram showing an embodiment of the present invention. In the figure, 1 is a representative color extraction unit, 2 is a limited color image generation unit, 3 is a foreground / background separation unit, 4 is a contour determination unit, 5 is a color number determination unit, 6 is a color difference calculation unit, and 7 is a modified representative color selection. Part 8 is a color replacement part.

  The representative color extraction unit 1 previously extracts representative colors from the entire processing target image. The method for extracting the representative color is not limited, and may be performed using various known methods. For example, a method described in Patent Document 1 may be used. Note that the number of representative colors may be limited to a predetermined number of colors.

  The limited color image generation unit 2 converts the color of each pixel of the given processing target image into one of the representative colors extracted by the representative color extraction unit 1 and generates a limited color image in advance. The method for converting to any of the representative colors is not limited, and may be performed using various known methods. For example, a method of converting to a representative color having the smallest color difference or a method described in Patent Document 1 may be used. Note that the function of the limited color image generation unit 2 may be integrated into a color replacement unit 8 described later.

  The foreground / background separation unit 3 separates a processing area having a predetermined size including the target pixel from the given processing target image into a foreground area and a background area. The determination of the foreground region or the background region in each pixel may be performed using the processing target image, and the method is not limited, and may be performed using various known methods. Note that the size of the processing area may be changed by the color number determination unit 5. The separation result into the foreground area and the background area is passed to the color difference calculation unit 6 and the color replacement unit 8.

  The contour determination unit 4 determines whether or not the target pixel is a contour region. The method for determining whether or not the region is a contour region is not limited, and may be performed using various known methods such as a contour detection filter. The determination result is passed to the color difference calculation unit 6 and the color replacement unit 8. In addition, you may comprise without providing this outline determination part 4. FIG.

  The color number determination unit 5 determines the number of colors in the processing region used in the foreground / background separation unit 3. The determination may be made, for example, by determining whether the background region color is one color and the foreground region color is two colors or less, or three or more colors. As a determination method, for example, a principal component analysis may be performed on the color of each pixel in the processing region, and the number of colors larger than a predetermined value may be counted to determine the count value. Or you may determine whether the variance value of a background color or a foreground color is larger than a predetermined value. Alternatively, although not illustrated in FIG. 1, for example, the limited color image generated by the limited color image generation unit 2 may be used to determine the number of representative colors used in the processing area in the limited color image. The determination result is passed to the color replacement unit 8 in the example shown in FIG. In addition, when it is determined that the number of colors is 3 or more, the size of the processing area may be changed to be smaller than the current size. In this case, processing is performed using a processing area whose size has been changed in each unit that uses the processing area. For example, the foreground / background separator 3 separates the foreground area and the background area in the changed processing area. Note that it is possible to repeat the determination of the number of colors and repeat the change of the size of the processing region in the processing region whose size has been changed, but a limit is set so as not to change the size smaller than a predetermined size. Good. You may comprise without providing this color number determination part 5. FIG.

The color difference calculation unit 6 calculates the color difference between the foreground area color and the background area color. The color difference is the distance between two colors in the color space. For example, in the RGB color space, the color difference ΔE between two colors can be calculated from ΔR, ΔG, ΔB, which are differences between the color components of the two colors.
ΔE = (ΔR ² + ΔG ² + ΔB ² ) ^1/2
It can be obtained by As the colors of the foreground area and the background area, it is preferable to obtain and use the average color of each pixel in the foreground area and the average color of each pixel in the background area based on the processing target image. Alternatively, the representative color corresponding to the foreground area and the representative color corresponding to the background area may be acquired based on the limited color image. When there are a plurality of similar representative colors in the foreground area or the background area, the average color of the representative color corresponding to each pixel in the foreground area and the average color of the representative color corresponding to each pixel in the background area are used. May be. For the foreground area or the background area, the separation result by the foreground / background separation unit 3 may be used. If the contour determination unit 4 determines that the region is outside the contour region, control may be performed so that the processing after the color difference calculation unit 6 is not performed.

  The corrected representative color selection unit 7 calculates the color difference calculated by the color difference calculation unit 6 from the representative colors extracted by the representative color extraction unit 1 when the color difference calculated by the color difference calculation unit 6 is smaller than a predetermined value. The corrected representative color corresponding to the foreground area or the corrected representative color corresponding to the background area is selected. Although the details of the selection method will be described later, the representative color corresponding to the foreground area and the representative color corresponding to the background area are selected according to the distance from the straight line passing through the average color of the foreground area and the average color of the background area in the color space. The corrected representative color may be selected according to the distance from the straight line that passes through. When a straight line that passes through the average color of the foreground area and the average color of the background area is used, a straight line that passes through a representative color corresponding to the foreground area and a representative color corresponding to the background area is also used, and an angle formed by the two straight lines is determined in advance. If the angle is larger than the angle, the corrected representative color may be selected regardless of the color difference calculated by the color difference calculation unit 6. Alternatively, for each of the two representative color sets obtained from the representative colors extracted by the representative color extraction unit 1, the two representative colors of the set, the foreground area color (for example, the average color), and the background area color (for example, the average) It is also possible to obtain the value of the evaluation function using the color), obtain a set of representative colors based on the value of the evaluation function, and select the corrected representative color. If there is no corrected representative color that satisfies a predetermined condition, the color difference between the representative color corresponding to the background area is determined in advance on a straight line passing the colors of the foreground area and the background area in the color space. A representative color larger than a predetermined value or a representative color having a color difference with a representative color corresponding to the foreground area larger than a predetermined value may be added and selected as a corrected representative color.

  The color replacement unit 8 replaces the color of the target pixel with the corrected representative color selected by the corrected representative color selection unit 7. When the target pixel is a pixel in the foreground area and the corrected representative color selection unit 7 selects a corrected representative color corresponding to the background area, or when the target pixel is a pixel in the background area and the corrected representative color is selected. When the modified representative color corresponding to the foreground area is selected in the unit 7, the color of the target pixel may not be changed. If the contour determination unit 4 does not determine that the region is an outline region, and if the number of colors determination unit 5 determines that the number of colors is three or more, the replacement with the corrected representative color is not performed. You may comprise. Further, instead of the limited color image generation unit 2, the color replacement unit 8 may be configured to convert the color of the pixel of interest into either a corrected representative color or another representative color.

  FIG. 2 is a flowchart showing an example of the operation in the embodiment of the present invention. In S11, the representative color extraction unit 1 extracts a representative color from the entire processing target image. In S12, the limited color image generation unit 2 converts the representative color corresponding to the color of each pixel of the processing target image in the color space, for example, the representative color having the smallest distance from the color of each pixel, to the limited color image. Is generated.

  In S13, an unprocessed pixel is set as a target pixel. In S14, the foreground / background separation unit 3 selects a foreground region for a processing region of a predetermined size including the target pixel from the given processing target image. Separate into background areas. In S15, the contour determination unit 4 determines whether or not the target pixel is a contour region. In S16, if it is determined in S15 that the pixel of interest is an outline region, the process proceeds to S17. If it is determined that the pixel of interest is not an outline region, the process proceeds to S23 without correcting the representative color. Note that the processing of S14 and S15 may not be performed.

  In S17, the color difference calculation unit 6 calculates the color difference between the foreground area color and the background area color. For example, the color difference between the average color of the foreground area and the average color of the background area in the processing target image, or the color difference between the representative color of the foreground area and the representative color of the background area in the limited color image may be obtained.

  In S18, the corrected representative color selection unit 7 determines whether or not the color difference obtained by the color difference calculation unit 6 in S17 is smaller than a predetermined value. If the color difference is larger than a predetermined value, it is determined that the color difference between the foreground and the background is clear even if it is as it is, and in this case, since the representative color is not changed, the process proceeds to S23.

  If the color difference is smaller than a predetermined value, it is determined that the color difference between the foreground and the background is not clearly reproduced, and a representative corresponding to the foreground area is set so as to increase the color difference in S19. The representative color corresponding to the color or background area is selected again to be the modified representative color. If there is no modified representative color that satisfies a predetermined condition, a representative color may be added and selected as the modified representative color.

  On the other hand, in S20, the color number determination unit 5 obtains the number of colors in the processing region, and determines in S21 whether the number of colors is two or less. If it is determined in S21 that there are two or less colors, the process proceeds to S22, and if it is determined that there are three or more colors, the process proceeds to S23 without replacing with the corrected representative color in S22. Note that the processing of S20 and S21 may be performed after S13 or before S19, or may be performed in parallel.

  In S22, the color replacement unit 8 replaces the color of the target pixel with the corrected representative color selected by the corrected representative color selection unit 7 in S19. In this operation example, the replacement with the corrected representative color is performed in the outline region, the number of colors in the processing region is two or less, and the color difference between the foreground region and the background region is determined based on the determinations in S16, S18, and S21. This is performed when the value is smaller than a predetermined value.

  In S23, it is determined whether or not each pixel of the processing target image has been processed as the target pixel. If there are any unprocessed pixels, the process returns to S13, and the process is repeated using the unprocessed pixels as the target pixel. When the process is completed, a limited color image in which the color difference is largely corrected for a portion where the color difference between the foreground region and the background region is smaller than a predetermined value in the limited color image generated in S12 is obtained.

  Some examples of the process of selecting the corrected representative color in the corrected representative color selection unit 7 will be described. FIG. 3 is an explanatory diagram of a first example of the corrected representative color selection process, and FIG. 4 is an explanatory diagram of an example of a selection range in the first example of the corrected representative color selection process. In this example, the corrected representative color is selected according to the distance from the straight line passing through the average color of the foreground area and the average color of the background area. In FIG. 3, P indicates the average color of the foreground area, Q indicates the average color of the background area, and T1, T2,... The color difference calculation unit 6 calculates the color difference between the average color of the foreground area and the average color of the background area, and the color difference between the color P and the color Q is smaller than a predetermined value. In FIG. 3A, the range of values for which the color difference is predetermined from the color Q is indicated by a broken line, and in FIG. 3B, the range of values for which the color difference is predetermined from the color P is indicated by a broken line. And the color Q are included in this range.

  The corrected representative color selection unit 7 considers a straight line passing through the average color P in the foreground area and the average color Q in the background area, and uses the representative color that increases the color difference as the corrected representative color according to the distance between the straight line and each representative color. select. First, in the direction from the average color Q of the background area to the average color P of the foreground area, the color difference from the average color Q of the background area is larger than a predetermined value according to the distance from the straight line. Select the corrected representative color. This case is shown in FIG. The corrected representative color selected in this case changes the representative color of the foreground area.

For example, the representative color having the shortest distance from the straight line may be selected as the corrected representative color. Alternatively, the distance from the average color Q in the background area is also considered, and the distance from the straight line is set to Lt and the distance from the average color Q in the background area is set to Lu for a certain representative color. D = αLt + βLu
And a representative color having the minimum value D may be selected as a corrected representative color. α and β are constants given in advance. In this case, the smaller the distance from the straight line, the easier it is to select, and the closer to the average color of the background region, the easier it is to select the color difference from the average color of the background region than a predetermined value.

  It should be noted that a condition may be set when selecting a representative color so that a representative color far from the color change from the average color Q of the background area to the average color P of the foreground area is not selected. For example, when the representative color is selected according to the distance from the straight line, if the distance from the straight line is larger than a predetermined value, the correction representative color in the direction from the color Q to the color P is not selected. Good. Furthermore, an upper limit of the color difference from the average color Q in the background region is provided, and when the color difference exceeds the upper limit, the corrected representative color is not selected. In this case, the color difference from the color Q exceeds the predetermined value range, is within the upper limit of the color difference, and is selected from representative colors whose distance from the straight line is within the predetermined value. Become.

Alternatively, as shown in FIG. 4A, a representative color is selected from representative colors within a conical region having the color Q as the center of the bottom surface, and the color difference from the color Q exceeds a predetermined value Lumin. Also good. In the example shown in FIG. 4A, a vector T having a predetermined length longer than the value Lumin in the direction toward the color P starting from the color Q is defined as a vector T, and the direction intersecting the vector T starting from the color Q. A set of vectors having a predetermined length shorter than the value Lumin is defined as a vector group U, and coefficients γ and δ are values of 0 or more and 1 or less,
γ · vector T + δ · (1−γ) · vector U
Is a conical region. The conical region may be selected from representative colors in which the color difference from the color Q exceeds a predetermined value Lumin. If there is no representative color satisfying this condition, the corrected representative color in the direction from the color Q to the color P is not selected.

  When calculating the above-mentioned value D, if the value D is larger than a predetermined value, the correction representative color in the direction from the color Q to the color P may not be selected. In this case, the range within which the value D is within a predetermined value corresponds to the conical region shown in FIG.

  If the corrected representative color is not selected in the direction from the average color Q of the background area to the average color P of the foreground area, the average color of the foreground area is changed from the average color P of the foreground area to the average color Q of the background area. A corrected representative color is selected from representative colors having a color difference from P larger than a predetermined value according to the distance from the straight line. This case is shown in FIG. The corrected representative color selected in this case changes the representative color of the background area.

For example, the representative color having the shortest distance from the straight line may be selected as the corrected representative color. Alternatively, the distance from the average color P in the foreground area is also considered, and the distance from the straight line is Lt and the distance from the average color P in the foreground area is Lv for a certain representative color. D = αLt + βLv
And the representative color that minimizes D may be selected as the corrected representative color. α and β are constants given in advance. In this case, the smaller the distance from the straight line, the easier the selection, and the closer the color to the foreground area is, the easier it is to select the color difference from the average color of the foreground area than a predetermined value.

  In this case as well, it is preferable to add a condition when selecting a representative color so that a representative color that is far from the color change from the average color P in the foreground area to the average color Q in the background area is not selected. For example, when the representative color is selected according to the distance from the straight line, if the distance from the straight line is larger than a predetermined value, the corrected representative color in the direction from the color P to the color Q is not selected. Good. Furthermore, an upper limit of the color difference from the average color P in the background area is provided, and when the color difference exceeds the upper limit, the corrected representative color is not selected. In this case, the color difference from the color P exceeds the predetermined value range, is within the upper limit of the color difference, and is selected from the representative colors whose distance from the straight line is within the predetermined value. Become.

Alternatively, as shown in FIG. 4B, a representative color is selected from representative colors that are within a conical region having the color P as the center of the bottom surface and the color difference from the color P exceeds a predetermined value Lumin. Also good. In the example shown in FIG. 4B, a vector T having a predetermined length longer than the value Lumin in the direction toward the color Q starting from the color P is defined as the vector T, and the direction intersecting the vector T starting from the color Q. A set of vectors having a predetermined length shorter than the value Lumin is defined as a vector group U, and coefficients γ and δ are values of 0 or more and 1 or less,
−γ · vector T + δ · (1−γ) · vector U
Is a conical region. The conical region may be selected from representative colors in which the color difference from the color P exceeds a predetermined value Lumin. If there is no representative color that satisfies this condition, the correction representative color in the direction from the color P to the color Q is not selected.

  When calculating the above-described value D, if the value D is larger than a predetermined value, the correction representative color in the direction from the color P to the color Q may not be selected. In this case, a range where the value D is within a predetermined value corresponds to the conical region shown in FIG.

  FIG. 5 is an explanatory diagram of an example of the representative color adding process. The corrected representative color is selected in the direction from the average color Q in the background area to the average color P in the foreground area, but is not selected, and the corrected representative color is changed in the direction from the average color P in the foreground area to the average color Q in the background area. If the color replacement unit 8 does not select the color, the color replacement unit 8 may not replace the color. However, the modified representative color selection unit 7 adds a new representative color, The representative color may be selected as the corrected representative color. For example, in the first example of the modified representative color selection process, the average color Q of the background region or the background region corresponds to a straight line passing through the average color P of the foreground region and the average color Q of the background region in the color space. Add a representative color whose color difference from the representative color is larger than a predetermined value, or a representative color whose color difference from the average color P in the foreground area or the representative color corresponding to the foreground area is larger than a predetermined value. The selected representative color may be selected as the corrected representative color.

  In addition, when adding a representative color whose color difference from the average color Q of the background area or the representative color corresponding to the background area is larger than a predetermined value, the average color P of the foreground area or the representative color corresponding to the foreground area Add to the side where the color difference is small. In addition, when a representative color having a color difference from the average color P of the foreground area or the representative color corresponding to the foreground area is larger than a predetermined value, the average color Q of the background area or the representative color corresponding to the background area is added. Add to the side where the color difference is small. In the example shown in FIG. 5, a representative color Ta whose color difference from the representative color T2 corresponding to the background area is larger than a predetermined value on a straight line passing through the average color P of the foreground area and the average color Q of the background area. An added example is shown. The added representative color Ta may be selected as the corrected representative color.

  Of course, in addition to adding a representative color whose color difference from the representative color corresponding to the background region or foreground region is larger than a predetermined value, the representative color corresponding to the background region and the representative color corresponding to the foreground region are sandwiched, Two representative colors whose color difference is larger than a predetermined value may be added on the above-mentioned straight line.

  In the limited color image generated by the limited color image generation unit 2, the foreground area and the background area may be associated with a certain representative color. In this case, even if there is a color difference between the background and the foreground in the processing target image, there is no distinction between the foreground area and the background area in the limited color image. Even in such a case, in the first example of the modified representative color selection process described above, if the modified representative color is selected using the average color of the foreground area and the average color of the background area, the limitation using the modified representative color is limited. In the color image, a foreground area and a background area appear.

  FIG. 6 is an explanatory diagram of a second example of the modified representative color selection process. In this example, a representative color corresponding to the foreground area and a representative color corresponding to the background area are used together with the average color of the foreground area and the average color of the background area. In the figure, P is the average color of the foreground area, Q is the average color of the background area, R is the representative color corresponding to the foreground area, S is the representative color corresponding to the background area, T1, T2,. Each color is shown. Further, the color difference between the colors P and Q is assumed to be smaller than a predetermined value. In FIG. 6A, the range of values for which the color difference is predetermined from the color Q is indicated by a broken line, and in FIG. 6B, the range of values for which the color difference is predetermined from the color P is indicated by a broken line. And the color Q are included in this range.

  In each of the foreground area and the background area, the average color of each area may be different from the representative color corresponding to each area. In that case, the direction of change in the average color of the foreground area and the background area and the change of the representative color The method may be different. An example of this case is shown in FIG. For example, in FIG. 6A, the direction from the average color Q of the background area to the average color P of the foreground area and the direction from the representative color S corresponding to the background area to the representative color R corresponding to the foreground area are expressed as angles. It differs by θ. Also in FIG. 6B, there are a direction from the average color P in the foreground area to the average color Q in the background area, and a direction from the representative color R corresponding to the foreground area to the representative color S corresponding to the background area. The angle θ is different. When the angle θ is larger than a predetermined angle, the limited color image generated using the representative color corresponding to the foreground area and the representative color corresponding to the background area has a tendency of color in the background area and the foreground area. Appears different from the image to be processed. Therefore, when the angle θ is larger than a predetermined angle, the corrected representative color is selected regardless of the magnitude of the color difference calculated by the color difference calculation unit 6. The method of selecting the corrected representative color is as described in the first example of the corrected representative color selection process described above. Since the corrected representative color is selected according to the distance from the straight line passing through the average color P of the foreground area and the average color Q of the background area, the colors of the foreground area color and the background area color are aligned. For this reason, a color difference is ensured and a difference in color tendency due to the limited color is prevented.

  FIG. 7 is an explanatory diagram of a third example of the corrected representative color selection process, and FIG. 8 is an explanatory diagram of an example of a selection range in the third example of the corrected representative color selection process. In this example, the corrected representative color is selected according to the distance from a straight line passing through the representative color corresponding to the foreground area and the representative color corresponding to the background area. In the figure, TP represents a representative color corresponding to the foreground area, TQ represents a representative color corresponding to the background area, and T1, T2,... Represent other representative colors. Further, the color difference calculation unit 6 obtains a color difference between the representative color TP corresponding to the foreground area and the representative color TQ corresponding to the background area, and the color difference between the representative color TP and the representative color TQ is larger than a predetermined value. Try to be small. In FIG. 7A, the range of values for which the color difference is predetermined from the representative color TQ is indicated by a broken line, and in FIG. 7B, the range of values for which the color difference is predetermined from the representative color TP is indicated by a broken line. The representative color TP and the representative color TQ are included in this range.

  The corrected representative color selection unit 7 considers a straight line that passes through the representative color TP corresponding to the foreground area and the representative color TQ corresponding to the background area, and selects a representative color that increases the color difference according to the distance between the straight line and each representative color. Select as the modified representative color. First, in a direction from the representative color TQ corresponding to the background area to the representative color TP corresponding to the foreground area, a straight line is selected from the representative colors in which the color difference from the representative color TQ corresponding to the background area is larger than a predetermined value. The corrected representative color is selected according to the distance between This case is shown in FIG. The corrected representative color selected in this case changes the representative color corresponding to the foreground area.

For example, the representative color having the shortest distance from the straight line may be selected as the corrected representative color. Alternatively, the distance from the representative color TQ corresponding to the background area is also considered, and the distance from the straight line for a certain representative color is Lt, and the distance from the representative color TQ corresponding to the background area is Lu. D = αLt + βLu
And the representative color that minimizes D may be selected as the corrected representative color. α and β are constants given in advance. In this case, the smaller the distance from the straight line, the easier the selection, and the closer to the representative color TQ corresponding to the background area under the condition that the color difference from the representative color TQ corresponding to the background area is larger than a predetermined value, the selection is made. It becomes easy to be done.

  It should be noted that a condition should be set when selecting a representative color so that a representative color far from a change in color from the representative color TQ corresponding to the background area to the representative color TP corresponding to the foreground area is not selected. . For example, when the representative color is selected according to the distance from the straight line, if the distance from the straight line is larger than a predetermined value, the corrected representative color in the direction from the representative color TQ to the representative color TP is not selected. It is good to do so. Furthermore, an upper limit of the color difference from the representative color TQ corresponding to the background area is provided, and when the color difference exceeds the upper limit, the corrected representative color is not selected. In this case, the color difference from the representative color TQ exceeds the predetermined value range, is within the upper limit of the color difference, and is selected from the representative colors whose distance from the straight line is within the predetermined value. become.

Alternatively, as shown in FIG. 8A, a representative color is selected from representative colors in a conical region having the representative color TQ as the center of the bottom surface, and the color difference from the representative color TQ exceeds a predetermined value Lumin. May be. In the example shown in FIG. 8A, a vector having a predetermined length longer than the value Lumin in the direction toward the representative color TP starting from the representative color TQ is set as the vector T, and the vector T starting from the representative color TQ as the starting point. A set of vectors having a predetermined length shorter than the value Lumin in the intersecting direction is defined as a vector group U, and coefficients γ and δ are set to values of 0 or more and 1 or less.
γ · vector T + δ · (1−γ) · vector U
Is a conical region. This conical region may be selected from representative colors whose color difference from the representative color TQ exceeds the range of a predetermined value Lumin. If there is no representative color satisfying this condition, the corrected representative color is not selected in the direction from the representative color TQ to the representative color TP.

  When calculating the above-described value D, if the value D is larger than a predetermined value, the corrected representative color may not be selected in the direction from the representative color TQ to the representative color TP. . In this case, the range within which the value D is within a predetermined value corresponds to the conical region shown in FIG.

  If the corrected representative color is not selected in the direction from the representative color TQ corresponding to the background area to the representative color TP corresponding to the foreground area, the direction is changed from the representative color TP corresponding to the foreground area to the representative color TQ corresponding to the background area. In the direction, the corrected representative color is selected from the representative colors having a color difference from the representative color TP corresponding to the foreground area larger than a predetermined value according to the distance from the straight line. This case is shown in FIG. The corrected representative color selected in this case changes the representative color corresponding to the background area.

For example, the representative color having the shortest distance from the straight line may be selected as the corrected representative color. Alternatively, the distance from the representative color TP corresponding to the foreground area is also considered, and the distance from a straight line for a certain representative color is Lt, and the distance from the representative color TP corresponding to the foreground area is Lv. D = αLt + βLv
And the representative color that minimizes D may be selected as the corrected representative color. α and β are constants given in advance. In this case, the smaller the distance from the straight line, the easier the selection, and the closer to the representative color TP corresponding to the foreground area under the condition that the color difference from the representative color TP corresponding to the foreground area is larger than a predetermined value, the selection is made. It becomes easy to be done.

  In this case as well, a condition is added when selecting a representative color so that a representative color far from the change in color from the representative color TP corresponding to the foreground area to the representative color TQ corresponding to the background area is not selected. It is good to leave. For example, when the representative color is selected according to the distance from the straight line, if the distance from the straight line is larger than a predetermined value, the corrected representative color in the direction from the representative color TP to the representative color TQ is not selected. It is good to do so. Furthermore, an upper limit of the color difference from the representative color TP corresponding to the background region is provided, and when the color difference exceeds the upper limit, the corrected representative color is not selected. In this case, the color difference from the representative color TP exceeds the predetermined value range, and is selected from the representative colors that are within the upper limit of the color difference and the distance from the straight line is within the predetermined value. become.

Alternatively, it is selected from representative colors in a conical region having the representative color TP as the center of the bottom surface as shown in FIG. 8B, and the color difference from the representative color TP exceeds a predetermined value Lumin. May be. In the example shown in FIG. 8B, a vector having a predetermined length longer than the value Lumin in the direction toward the representative color TQ with the representative color TP as the starting point is a vector T, and a vector T with the representative color TQ as the starting point. A set of vectors having a predetermined length shorter than the value Lumin in the intersecting direction is defined as a vector group U, and coefficients γ and δ are set to values of 0 or more and 1 or less.
−γ · vector T + δ · (1−γ) · vector U
Is a conical region. The conical region may be selected from representative colors whose color difference from the representative color TP exceeds a predetermined value Lumin. If there is no representative color that satisfies this condition, the modified representative color is not selected in the direction from the representative color TP to the representative color TQ.

  When calculating the above-described value D, if the value D is larger than a predetermined value, the corrected representative color in the direction from the representative color TP to the representative color TQ may not be selected. . In this case, a range where the value D is within a predetermined value corresponds to the conical region shown in FIG.

  FIG. 9 is an explanatory diagram of another example of representative color addition processing. The corrected representative color is selected in the direction from the representative color TQ corresponding to the background area to the representative color TP corresponding to the foreground area, but is not selected and the representative color corresponding to the background area is changed from the representative color TP corresponding to the foreground area. If the corrected representative color is selected in the direction toward TQ but is not selected, the color replacement unit 8 may be configured not to replace the color. A representative color may be added, and the representative color may be selected as the corrected representative color. For example, in the third example of the modified representative color selection process, the representative color TQ corresponding to the background region is on a straight line passing through the representative color TP corresponding to the foreground region and the representative color TQ corresponding to the background region in the color space. Alternatively, a representative color whose color difference from the average color of the background area is larger than a predetermined value, or a representative color whose color difference from the representative color TP corresponding to the foreground area or the average color of the foreground area is larger than a predetermined value. The added representative color may be selected as the corrected representative color.

  When a representative color having a color difference from the representative color TQ corresponding to the background area or the average color of the background area is larger than a predetermined value, the representative color TP corresponding to the foreground area or the average color of the foreground area is added. Add to the side where the color difference is small. Further, when adding a representative color whose color difference from the representative color TP corresponding to the foreground area is larger than a predetermined value, the color difference from the representative color TQ corresponding to the background area or the average color of the background area is small. Add to. In the example shown in FIG. 9, the color difference between the representative color TQ corresponding to the background region is larger than a predetermined value on a straight line passing through the representative color TP corresponding to the foreground region and the representative color TQ corresponding to the background region. An example in which a representative color Ta is added is shown. The added representative color Ta may be selected as the corrected representative color.

  Of course, in addition to adding a representative color whose color difference from the representative color corresponding to the background region or foreground region is larger than a predetermined value, the representative color corresponding to the background region and the representative color corresponding to the foreground region are sandwiched, Two representative colors whose color difference is larger than a predetermined value may be added on the above-mentioned straight line.

  FIG. 10 is an explanatory diagram of a fourth example of the modified representative color selection process. In this example, an example of selecting a representative color corresponding to the foreground area and a corrected representative color for correcting the representative color corresponding to the background area from the entire representative colors extracted by the representative color extraction unit 1 is used. Show. In the figure, P indicates the average color of the foreground area, Q indicates the average color of the background area, and T1, T2,... Further, the color difference calculation unit 6 obtains the color difference between the average color P in the foreground area and the average color Q in the background area, and the color difference between the average color P and the average color Q is smaller than a predetermined value. . In FIG. 10, a range of values in which the color difference is predetermined from the average color Q is indicated by a broken line, and the average color P and the average color Q are included in this range.

Two representative colors are selected from the extracted representative colors to obtain a set of representative colors, and the value of the evaluation function using the average color of the foreground area and the average color of the background area is obtained for the set of representative colors. As an example of the evaluation function H, for example, two representative colors constituting a set of representative colors are Ci and Cj, and an average color P in the foreground area and an average color Q in the background area are used.
H = α (| P−Ci | + | Q−Cj |) −β (| Ci−Cj |)
It is good to do. α and β are constants given in advance. The term (| P-Ci | + | Q-Cj |) indicates an error when the representative color set is replaced with a corrected representative color. The smaller this error, the better. Further, (| Ci−Cj |) is a color difference between representative colors. The larger the color difference, the better. The condition is that the color difference (| Ci−Cj |) of the representative color is larger than a predetermined value used when determining the color difference calculated by the color difference calculation unit 6. The value of the evaluation function H is smaller as the error is smaller and the color difference is larger. Therefore, the representative color set having the smallest evaluation function H value among the representative color sets may be used as the corrected representative color.

  In the example shown in FIG. 10, six representative colors T1, T2, T3, T4, T5, and T6 are shown. For example, when a limited color image is generated by the limited color image generation unit 2, if a representative color having the smallest color difference from the colors of the foreground area and the background area is selected, the representative color T1 is selected as the representative color corresponding to the foreground area. The representative color T2 is selected as the representative color corresponding to the area. However, since the color difference is smaller than a predetermined value in the set of the representative color T1 and the representative color T2, this set of representative values is not selected.

  The set of representative colors includes 30 sets of permutations of six representative colors including the set of representative colors T1 and T2. Among them, as described above, the color difference is smaller than a predetermined value in the set in which the representative color T1 is Ci, the representative color T2 is Cj, and the set in which the representative color T2 is Ci and the representative color T1 is Cj. Therefore, it is excluded. For example, when the representative color T3 is Ci and the representative color T2 is Cj, the value of the evaluation function is the smallest. Therefore, the corrected representative color corresponding to the foreground area may be the representative color T3, and the corrected representative color corresponding to the background area may be the representative color T2. When the representative color T2 is Ci and the representative color T3 is Cj, the values of | P−Ci | and | Q−Cj | are larger than the above-described group, and the value of the evaluation function is also large.

  Of course, the above-described evaluation function is an example, and the present invention is not limited to this example, and various functions for evaluating two sets of representative colors may be used. Further, instead of the average color P in the foreground area and the average color Q in the background area, a representative color corresponding to the foreground area and a representative color corresponding to the background area may be used.

  In addition, you may provide conditions with respect to the value obtained using the evaluation function. For example, when there is an upper limit for the value of the evaluation function H described above and there is no representative color that satisfies the condition when the minimum value of the evaluation function H obtained from each set of representative colors is greater than a predetermined upper limit As such, it may be configured not to select the corrected representative color. If the corrected representative color is not selected, the color replacement unit 8 may be configured not to perform color replacement. Alternatively, for example, a new representative color may be added by the corrected representative color selection unit 7 by the method described with reference to FIG. 5 or FIG. 9 and the representative color may be selected as the corrected representative color.

  When the modified representative color selection process is performed by the above-described examples or other various methods, the color replacement unit 8 modifies the representative color corresponding to the foreground area when the target pixel is a pixel in the foreground area. If the representative color is selected, or if the target pixel is a pixel in the background area and a modified representative color that changes the representative color corresponding to the background area is selected, the color of the target pixel is corrected. Replace with. If the representative colors corresponding to both the foreground area and the background area are selected as the corrected representative colors, the corrected representative color depends on whether the target pixel is a pixel in the foreground area or a background area. And the color of the pixel of interest may be replaced. Note that when the corrected representative color is not selected, the color replacement may not be performed.

  FIG. 11 is a block diagram showing a modification of the embodiment of the present invention. In this modified example, it is assumed that an image in which only a predetermined number of colors or less is used as a processing target image or an image that has undergone limited color processing is given. In such a case, the limited color process need not be performed again, and the limited color image generation unit 2 is not provided in this modification. In this case, the average color of the foreground area and the representative color corresponding to the foreground area, and the average color of the background area and the representative color corresponding to the background area may be considered equivalent. Therefore, the color difference calculation unit 6 may calculate the color difference between the representative color corresponding to the foreground region and the representative color corresponding to the background region, and the modified representative color selection unit 7 corresponds to the representative color and background region corresponding to the foreground region. The corrected representative color may be selected according to the distance from the straight line passing through the representative color. For example, the corrected representative color may be selected by each example other than the second example of the selection process of the corrected representative color and other selection methods. The color replacement unit 8 may replace the color of the pixel of interest in the given processing target image with the corrected representative color.

  FIG. 12 is a flowchart showing an example of the operation in the modification of the embodiment of the present invention. In S11, the representative color extraction unit 1 extracts a representative color from the entire processing target image. S13, S14, S15, and S16 are as described above with reference to FIG.

  In S17, the color difference calculation unit 6 calculates the color difference between the representative color of the foreground area and the representative color of the background area. S18 is as described above with reference to FIG. If it is determined in S18 that the color difference is smaller than a predetermined value, in S19, the representative color corresponding to the foreground area and the representative color corresponding to the background area are used, and the foreground area is set so that the color difference becomes large. A corresponding representative color or a representative color corresponding to the background area is selected again to be a corrected representative color. If there is no modified representative color that satisfies a predetermined condition, a representative color may be added and selected as the modified representative color.

  S20 and S21 are as described above with reference to FIG. In S22, the color replacement unit 8 replaces the color of the target pixel of the processing target image with the corrected representative color selected by the corrected representative color selection unit 7 in S19. For example, when the target pixel is a pixel in the foreground area and a modified representative color for changing the representative color corresponding to the foreground area is selected, or the representative pixel is a pixel in the background area and corresponding to the background area When the corrected representative color whose color is to be changed is selected, the color of the pixel of interest may be replaced with the corrected representative color. S23 is as described above with reference to FIG.

  FIG. 13 is an explanatory diagram of an example of a computer program, a storage medium storing the computer program, and a computer when the functions described in the embodiment of the present invention and the modifications thereof are realized by a computer program. In the figure, 41 is a program, 42 is a computer, 51 is a magneto-optical disk, 52 is an optical disk, 53 is a magnetic disk, 54 is a memory, 61 is a CPU, 62 is an internal memory, 63 is a reading unit, 64 is a hard disk, and 65 is An interface 66 is a communication unit.

  You may implement | achieve the function of each part demonstrated by one Embodiment and its modification of the above-mentioned this invention entirely or partially with the program 41 which a computer performs. In that case, the program 41 and the data used by the program may be stored in a storage medium read by the computer. The storage medium causes a change state of energy such as magnetism, light, electricity, etc. to the reading unit 63 provided in the hardware resource of the computer according to the description content of the program, and the signal corresponding thereto In this format, the description content of the program is transmitted to the reading unit 63. For example, there are a magneto-optical disk 51, an optical disk 52 (including a CD and a DVD), a magnetic disk 53, a memory 54 (including an IC card, a memory card, a flash memory, and the like). Of course, these storage media are not limited to portable types.

  The program 41 is stored in these storage media, and the program 41 is read from the computer by, for example, mounting these storage media on the reading unit 63 or the interface 65 of the computer 42, and the internal memory 62 or the hard disk 64 (magnetic disk) And the functions described as the embodiment of the present invention and the modifications thereof are realized in whole or in part. Alternatively, the program 41 is transferred to the computer 42 via the communication path, and the computer 42 receives the program 41 by the communication unit 66 and stores it in the internal memory 62 or the hard disk 64, and the program 41 is executed by the CPU 61. May be.

  In addition, the computer 42 may be connected to various devices via an interface 65. For example, the processing described in the embodiment of the present invention and the modification thereof is performed with an image reading device connected via the interface 65 and an image read by the image reading device or an image obtained by processing the image as a processing target image. May be performed. The limited color image after processing may be passed to another program, stored in the hard disk 64, stored in a storage medium via the interface 65, or transferred to the outside through the communication unit 66. When storing or transferring, the limited color image may be compressed. When storing or transferring, the data amount is reduced as compared with the case where the limited color image is not used. Further, an image forming apparatus may be connected via the interface 65, and a limited color image after processing may be formed by the image forming apparatus.

  Of course, it may be partially configured by hardware, or all may be configured by hardware. Or you may comprise as a program which included all or one part of the function demonstrated with one Embodiment and its modification of this invention with other structures. Of course, when applied to other purposes, it may be integrated with the program for that purpose.

  DESCRIPTION OF SYMBOLS 1 ... Representative color extraction part, 2 ... Limited color image generation part, 3 ... Foreground / background separation part, 4 ... Contour determination part, 5 ... Color number determination part, 6 ... Color difference calculation part, 7 ... Modified representative color selection part, 8 ... Color replacement unit, 41 ... Program, 42 ... Computer, 51 ... Magneto-optical disk, 52 ... Optical disk, 53 ... Magnetic disk, 54 ... Memory, 61 ... CPU, 62 ... Internal memory, 63 ... Reading unit, 64 ... Hard disk, 65: Interface, 66: Communication unit.

Claims (11)

  Extraction means for extracting a representative color from the processing target image; separation means for separating a processing area of a predetermined size including the target pixel in the processing target image into a foreground area and a background area; and a color of the foreground area And a calculating means for calculating a color difference between the colors of the background area, and a representative color corresponding to the foreground area in the color space and the background area when the color difference calculated by the calculating means is smaller than a predetermined value. Selecting means for selecting a corrected representative color corresponding to the foreground area or a corrected representative color corresponding to the background area, which increases a color difference from the representative colors extracted by the extracting means according to a distance from a straight line passing through the representative color; An image processing apparatus comprising replacement means for replacing the color of the target pixel with the corrected representative color selected by the selection means.   Extraction means for extracting a representative color from the processing target image; separation means for separating a processing area of a predetermined size including the target pixel in the processing target image into a foreground area and a background area; and a color of the foreground area And a calculating means for calculating a color difference between the colors of the background area, and an average color of the foreground area and an average color of the background area in a color space when the color difference calculated by the calculating means is smaller than a predetermined value. Selecting means for selecting a corrected representative color corresponding to the foreground area or a corrected representative color corresponding to the background area, which increases a color difference from the representative colors extracted by the extracting means according to a distance from a straight line passing therethrough; and the selecting means An image processing apparatus comprising: a replacement unit that replaces the color of the target pixel with the corrected representative color selected in step (1).   The selection means has an angle formed by a straight line passing through an average color of the foreground area and an average color of the background area in a color space, and a straight line passing through a representative color corresponding to the foreground area and a representative color corresponding to the background area. 3. The image processing apparatus according to claim 2, wherein when the angle is larger than a predetermined angle, the corrected representative color is selected regardless of the color difference calculated by the calculation unit.   Extraction means for extracting a representative color from the processing target image; separation means for separating a processing area of a predetermined size including the target pixel in the processing target image into a foreground area and a background area; and a color of the foreground area And a calculating means for calculating a color difference between the colors of the background region, and a set of two representative colors obtained from the representative color extracted by the extracting means when the color difference calculated by the calculating means is smaller than a predetermined value. The color difference between one of the representative colors of the set and the color of the foreground area and the color difference of the other representative color and the color of the background area are determined as errors, and the color difference between the two representative colors is used together with the error. A value of the evaluation function is obtained, a set of representative colors is obtained from the value of the evaluation function, and the corrected representative color and the background region corresponding to the foreground region that increases the color difference from the representative colors extracted by the extraction unit are obtained. Corresponding The image processing apparatus characterized by comprising selecting means for selecting as a modified representative color, a replacement means for replacing the color of the pixel of interest in the modified representative color selected by the selection means.   The selection means includes a representative color corresponding to the background region on a straight line passing through the color of the foreground region and the color of the background region in a color space when the modified representative color satisfying a predetermined condition does not exist. A representative color having a color difference greater than a predetermined value or a representative color having a color difference with a representative color corresponding to the foreground area greater than a predetermined value is added and selected as the corrected representative color. The image processing apparatus according to any one of claims 1 to 4.   The calculation means calculates a color difference using a representative color corresponding to the foreground area as a color of the foreground area and using a representative color corresponding to the background area as a color of the background area. The image processing apparatus according to any one of claims 1 to 5.   The calculating means uses an average color of each pixel in the foreground area or an average color of a representative color corresponding to each pixel as a color of the foreground area, and an average color of each pixel in the background area as a color of the background area. The image processing apparatus according to claim 1, wherein a color difference is calculated using an average color of representative colors corresponding to each pixel.   Further, the image processing apparatus further comprises contour determination means for determining whether or not the target pixel is a contour area, and the replacement means replaces the target pixel determined to be the contour area by the contour determination means. The image processing apparatus according to any one of claims 1 to 7.   Furthermore, it has color number determination means for determining the number of colors in the processing area, and the replacement means does not perform replacement on a pixel of interest for which the number of colors is determined to be 3 or more by the color number determination means. The image processing apparatus according to claim 1, wherein the image processing apparatus is characterized.   Furthermore, it has a color number determination means for determining the number of colors in the processing area, and the separation means determines the size of the processing area when the color number determination means determines that the number of colors is 3 or more. The image processing apparatus according to claim 1, wherein the foreground area and the background area are separated by changing the size to be smaller than a current size.   An image processing program for causing a computer to execute the function of the image processing apparatus according to any one of claims 1 to 10.

Images