JP4440487B2 - Color image color classification method and color image processing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image color classification method and a color image processing apparatus, and more particularly to a method of classifying pixels of a color image read by digitally scanning a color original into chromatic / achromatic pixels, and so on. The present invention relates to a color image processing apparatus including a mechanism for proper classification.
[0002]
[Prior art]
For example, in a color copier, black letters and black thin lines must be hit with a single black ink so that the outline can be seen clearly, and other color halftone parts must be hit with a combination of C, M, Y, and K inks. In order to do so, it is necessary to detect black characters and black lines in the image in advance. Normally, the combination of edge detection and chromatic / achromatic color determination is combined with black characters and black lines for the solid color and black edges detected by edge detection, and only those portions that are achromatic by chromatic / achromatic color determination. It is determined.
[0003]
The chromatic color portion includes a color halftone portion expressed by C, M, Y, and K halftone dots in addition to a solid color character and the like. Since it is difficult to determine, chromatic / achromatic color determination is performed based on the average saturation of the target pixel as shown in FIG.
[0004]
By the way, when a color original containing black characters or black lines is digitally scanned and read by a scanner, for example, as shown in FIG. 2 and FIG. 3, color blur occurs around the black edge, and the achromatic pixel in that portion. As a result of determining that the pixel is a chromatic color pixel, there is a problem that it cannot be clearly printed with a single black color.
[0005]
As described in Japanese Patent Laid-Open No. 4-90673, when a black component of a predetermined amount or more is included in the vicinity of the target pixel, the target pixel is determined to be a chromatic color based on the average saturation. Even so, according to the method of correcting the determination to an achromatic color, it is possible to solve the problem of erroneously determining an achromatic pixel in a color blur area generated in an edge portion such as a black character as a chromatic color pixel.
[0006]
[Problems to be solved by the invention]
However, in the above-described conventional method, a pixel in a low-saturation halftone dot region that includes a black component on average may be erroneously determined as an achromatic pixel.
[0007]
A large halftone dot region is determined as a halftone dot by separately performing halftone dot detection, and is hit by a combination of C, M, Y, and K inks for color halftones. Therefore, the chromatic color pixel is mistaken for an achromatic color pixel. Even if it is determined, there is no inconvenience.
[0008]
However, halftone dots in small areas such as halftone characters (color or gray characters expressed by halftone dots) are difficult to extract halftone dot characteristics and cannot be expected to have sufficient halftone dot detection accuracy. A part that is determined to be a character is generated although it is a key part. And if that part is a low-saturation color that contains black to some extent, it contains a black component in the vicinity, so it is clearly a colored part, but it is judged as an achromatic color and black only As a result, the inconvenience that the colored characters are printed in black and low quality characters are output.
Therefore, the present inventor has determined that a black edge is located when a black region is localized or a black region and a white region are present across the target pixel within a predetermined region centered on the target pixel determined to be chromatic. We have developed a chromatic / achromatic region determination method and apparatus that determines a pixel that blurs the surrounding color and corrects the chromatic determination to an achromatic determination. According to this method and apparatus, it is possible to determine only the pixels that bleed around the black edge as an achromatic color without correcting to a halftone area having a low saturation including an average black component. it can.
[0009]
The present invention has been made for the purpose of further improving the above-described method and apparatus developed by the present inventors, such as a black edge having a larger color fringe width without increasing the hardware scale. An object of the present invention is to provide a color image color classification method and a color image processing apparatus capable of determining a color blur achromatic.
[0010]
[Means for Solving the Problems]
The color image color classification method according to the present invention is a color image color that determines, for each pixel, a chromatic color and an achromatic color of an input image signal from each component signal of the input color image signal obtained by digitally scanning a color original. In the classification method, when a black region is localized within a predetermined region centered on the pixel of interest, or when a black region and a white region exist with the pixel of interest in between, the pixel of interest is caused by a color shift at the time of scanner input. The pixel is determined to be a black edge color blur pixel and is determined to be an achromatic pixel, and the pixel around the target pixel is extended by a predetermined number of pixels from the target pixel in the direction from the black region to the opposite non-black region within the predetermined region. The pixel is determined to be achromatic.
[0011]
In order to realize the color image color classification method described above, the invention of the color image processing apparatus according to the present invention determines that the pixel of interest is a black edge color blur pixel due to color shift at the time of scanner input, and achromatic pixel A first determination means that is fixed to the first pixel, and a pixel around the target pixel that is extended from the target pixel by a predetermined number of pixels in a direction from the black region to the opposing non-black region in the predetermined region 2 determination means.
[0012]
With the above configuration of the present invention, when viewing a larger area including the target pixel, a larger color blur width without increasing the hardware scale such as an increase in the size of the line memory necessary for the determination process Chromatic color judgment due to color blurs such as black edges can be corrected to achromatic color judgments, and even if there are color blurs such as black edges when scanning originals when reading originals from color copiers, etc. These can be reproduced in black.
[0013]
Further, in the color image color classification method and color image processing apparatus according to the present invention, when the extension of the achromatic determination is performed in a predetermined direction, the color blur of the black edge is known when the direction in which the color blur is generated is known. By limiting the extension of the achromatic determination of the judgment pixel only to that direction, the halftone dot area that contains the black component on the average and that has been able to be chromatically determined in the past is not erroneously determined as achromatic. be able to.
[0014]
Further, in the color image color classification method and color image processing apparatus according to the present invention, when the number of pixels for achromatic determination extension is changed according to the magnification ratio of the original, the color of the black edge when the magnification ratio is high By increasing the number of pixels for the achromatic determination extension of the blur determination pixels, a halftone area with a low saturation that includes black components on average, which was previously chromatically determined when the scaling ratio is not high, is erroneously excluded. It is possible not to make the color determination.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment (hereinafter referred to as this embodiment) of a color image color classification method and a color image processing apparatus according to the present invention will be described below with reference to the drawings.
FIG. 4 shows a schematic block diagram of an embodiment of the present invention.
In FIG. 1, an RGB signal (8 bits each) as an input image signal is converted into a YMC signal (1 bit each) by a color conversion unit 1 and input to a chromatic / achromatic color determination unit 2 and a black edge color blur determination unit 3, respectively. The
[0016]
From the chromatic / achromatic color determination unit 2, a primary chromatic / achromatic color determination result is output to the correction unit 4 in units of pixels.
[0017]
The black edge color blur determination unit 3 includes a first determination unit 3a and a second determination unit 3b. The determination result from the first determination means 3a as to whether or not the pixel is a black edge color bleeding pixel, and the determination result from the second determination means 3b regarding the pixel on the extension to the correction unit 4 respectively. Is output.
[0018]
At this time, in the first determination unit 3a, when the black region is localized within a predetermined region centered on the target pixel, or when the black region and the white region exist with the target pixel in between, the target pixel is determined. It is determined that the pixel has a black edge color blur due to color shift at the time of scanner input.
[0019]
Further, the second determination unit 3b determines pixels around the target pixel that are extended from the target pixel by a predetermined number of pixels in a direction from the black region to the opposing non-black region in the predetermined region. The second determination means 3b extends the achromatic determination in a predetermined direction. Further, the second determination means 3b changes the number of pixels for extending the achromatic determination according to the magnification of the document.
[0020]
The correction unit 4 corrects the determination result to the achromatic color determination only in the case of the black edge color blur determination pixel or its extension pixel with respect to the pixel for which the chromatic color determination is performed by the chromatic / achromatic color determination unit 2. The chromatic / achromatic color determination result is determined and output from the correction unit. In addition, when the chromatic / achromatic color determination unit 2 determines that the chromatic color is not determined to be a black edge color blur pixel, the chromatic color determination is finalized. In addition, the pixel for which the achromatic color is determined by the chromatic / achromatic color determination unit 2 is determined to be the achromatic color determination regardless of whether the pixel is determined to be a black edge color blur pixel.
[0021]
The color conversion unit 1 and the chromatic / achromatic color determination unit 2 will be further described.
[0022]
In this embodiment, whether the conversion from RGB signals (8 bits each) to YMC signals (1 bit each) is included in the hue of Y, R, M, B, C, or G for each pixel by the RGB signal. A chromatic color / achromatic color is determined for each hue by comparing the difference between the threshold value provided for each hue and the maximum and minimum RGB signal values. For example, when it is determined that the hue is included in Red, the chromatic color is determined by comparing the difference between the red threshold th_R and the maximum and minimum RGB signal values. As a result, if chromatic color is determined, Y = M = 1, C = 0. Similarly, when the hue is determined to be other hues, chromatic colors are determined using the threshold values for each hue (th_Y, th_M, th_B, th_C, th_G), and Y, M, C are determined according to the result and hue. Output 1/0 of. (Y: Y = 1, M = 0, C = 0, M: Y = 0, M = 1, C = 0, B: Y = 0, M = 1, C = 1, C: Y = 0, M = 0, C = 1, G: Y = 1, M = 0, C = 1) Next, the chromatic / achromatic color determination unit 2 uses the image signal converted to the CMY signal (each 1 bit) to generate a network. In order to determine the chromatic / achromatic color of the point, the average saturation in the small block area (NxN pixel area) including the neighborhood of the pixel of interest is calculated, and the chromatic / achromatic color of the pixel of interest is calculated. Determine. This is done by counting the number of pixels where Y, M, and C are 1 in the small block area, and comparing the difference between the maximum and minimum numbers with a predetermined threshold. Otherwise, it is determined as an achromatic color.
[0023]
Next, the first determination unit 3a of the black edge color blur determination unit 3 will be described. In this embodiment, a color blur area is determined using a 5 × 5 pixel block with N = 5.
[0024]
FIG. 5 is a block diagram of the first determination means 3a for the above determination algorithm. In FIG. 5, reference numerals 11 to 14 are counters, reference numerals 15 to 38 are comparators, reference numerals 39 to 54 are AND circuits, and reference numeral 55 is an OR circuit. The output of the OR circuit 55 becomes the determination output of the first determination means 3a.
[0025]
The counter 11 has a pixel count of C = 1, a pixel count of M = 1, and a pixel count of Y = 1 in each of the divided areas A 1 and B 2 obtained by dividing a small area of 5 × 5 pixels centered on the target pixel as shown in FIG. 1 is counted, and the minimum count value (0LQ A1, 0LQ B1) and the maximum count value (0D [A1, 0D [B1) are obtained. Since C = M = Y = 1 for the black pixels, the minimum count values (0LQ A1, 0LQ B1) are almost equal to the number of black pixels in the divided areas A 1, B, and can be used as a scale for the black component. In addition, since C = M = Y = 0 in the white pixel, the value obtained by subtracting the maximum count value (0D [A1, 0D [B1) from the total number of pixels in the divided area (here, 15) is the divided area A. , B is approximately equal to the number of white pixels in B, and can be used as a measure of the white component.
[0026]
Similarly, the counter 12 has the number of pixels of C = 1 and the number of pixels of M = 1 in each of the divided regions A and B obtained by dividing a small region of 5 × 5 pixels centered on the target pixel as shown in FIG. , Y = 1, and the minimum count value (0LQ A2, 0LQ B2) and the maximum count value (0D [A2, 0D [B2) are obtained. The counter 13 has a pixel count of C = 1, a pixel count of M = 1, and a pixel count of Y = 1 in each of the divided areas A 1 and B 2 obtained by dividing a small area of 5 × 5 pixels centered on the target pixel as shown in FIG. The number of pixels of 1 is counted, and the minimum count value (0LQ A3, 0LQ B3) and the maximum count value (0D [A3, 0D [B3) are obtained. The counter 14 has a number of pixels of C = 1, a number of pixels of M = 1, and a number of pixels Y = Y in each of the divided regions A and B obtained by dividing a small region of 5 × 5 pixels centered on the target pixel as shown in FIG. The number of pixels of 1 is counted, and the minimum count value (0LQ A4, 0LQ B4) and the maximum count value (0D [A4, 0D [B4)] are obtained.
[0027]
The comparators 15 to 20 and the AND circuits 39 to 42 are parts for performing the above-described condition determination on the divided areas A and B shown in FIG. 6 based on the output value of the counter 11. That is, the comparators 16 and 19 determine that the divided areas A and B are black areas when the minimum values 0LQ A1 and 0LQ B1, that is, when the black components of the areas A and B exceed the predetermined threshold th_K, respectively. Otherwise, it is judged as a non-black area and 0 is output. The comparators 17 and 18 are for making a determination regarding the ratio of the black components in the divided areas A and B. The comparator 17 multiplies 0LQ A1 by a predetermined threshold th_r (greater than 0 and less than 1). 1 is output when 0LQ B1 is smaller than the value, and the comparator 18 outputs 1 when 0LQ A1 is smaller than a value obtained by multiplying 0LQ B1 by a predetermined threshold th_r. Therefore, when the divided area A is a black area and the ratio of the black component of the divided area B to the black component is equal to or less than a predetermined value, the output of the AND circuit 40 becomes 1, so that the output of the OR circuit 55, that is, the first The determination output of the determination means 3a becomes 1. Similarly, when the divided region B is a black region and the ratio of the black component of the divided region A to the black component is equal to or less than a predetermined value, the output of the AND circuit 41 becomes 1, and therefore the determination by the first determination means 3a. The output becomes 1. The comparator 15 determines that the divided area B is a white area when a value obtained by subtracting 0D [B1 from the total number of pixels R of the divided area B, that is, when the white component of the divided area B exceeds a predetermined threshold th_W. Is output. Similarly, the comparator 20 determines that the divided area A is a white area when a value obtained by subtracting 0D [A1 from the total number of pixels R in the divided area A, that is, when the white component of the divided area A exceeds a predetermined threshold th_W. 1 is output. Therefore, when the divided area A is a black area and the divided area B is a white area, the output of the AND circuit 39 is 1, and as a result, the determination output of the first determination means 3a is 1. Similarly, when the divided area B is a black area and the divided area A is a white area, the output of the AND circuit 42 is 1, and the determination output of the first determination means 3a is 1.
[0028]
The comparators 21 to 26 and the AND circuits 43 to 46 are parts for performing the same condition determination on the divided areas A and B shown in FIG. 7 based on the output value of the counter 12. The comparators 27 to 32 and the AND circuits 47 to 50 are parts for performing the same condition determination on the divided areas A and B shown in FIG. 8 based on the output value of the counter 13. The comparators 33 to 38 and the AND circuits 51 to 54 are parts for performing the same condition determination on the divided areas A and B shown in FIG. 9 based on the output value of the counter 14.
[0029]
Summarizing the above description, horizontal (division pattern # 1 in FIG. 6) and vertical (division pattern # 1 in FIG. 6) and vertical (in FIG. 7) in the small block region (5 × 5 pixel block) of the input image signal centered on the pixel determined to be a chromatic color. 2 divisional pattern # 2) or 45 ° diagonally (division pattern # 3 in FIG. 8, division pattern # 4 in FIG. 9), and includes two symmetrical 5 × 3 pixels including one column of pixels including the central pixel. The pixel area (A, B) is divided into two, and at least one of the divided areas is determined to be a black area containing a black component equal to or greater than a predetermined threshold, and the black component of the black area is When the ratio of the black component of the area is equal to or smaller than the threshold value, or at least one of the divided areas is a black area including a black component equal to or larger than the predetermined threshold value and the other opposing area is equal to or larger than the predetermined second threshold value. Color bleed area when white component is included Judge as area. The division patterns in FIGS. 6 to 9 show an example where N = 5, but N is the same for other odd numbers.
Next, the 2nd determination means 3b is demonstrated.
[0030]
First, the second determination unit 3b determines pixels around the target pixel that are extended from the target pixel by a predetermined number of pixels in the predetermined area in the direction from the black region to the opposing non-black region.
In the case of the present embodiment, the extension direction of the achromatic determination is a direction from one (black region) to the other (non-black region or white region) of the two-region divided patterns in FIGS. As shown, the pixel direction is any one of eight adjacent pixel directions of up, down, left, right, diagonal upper right, diagonal lower right, diagonal upper left, and diagonal lower left.
[0031]
Specifically, in the example of FIG. 11 corresponding to FIG. 6, the extension direction of the achromatic determination is downward. In this case, when the target pixel is determined to be achromatic, the adjacent pixel on the lower side is further determined to be achromatic. In addition to the target pixel determined to be blurred by the black edge color, the primary determination result of the chromatic / achromatic color determination unit 2 is forcibly determined by the correction unit in the next stage for the extended pixel as well. It is corrected to.
[0032]
The second determination means 3b extends the achromatic determination in a predetermined direction.
For example, when it is known that the direction in which large color bleeding occurs is limited to the sub-scanning direction (up or down), black is only applied when the extension direction is one of the two directions up or down. Extending the achromatic determination by edge color blur determination.
[0033]
Further, the second determination means 3b changes the number of pixels for extending the achromatic determination according to the magnification of the document.
For example, the number of pixels for achromatic determination extension can be set to 0 for magnification up to 200%, 1 for 300%, and 2 for 400%. The number of extended pixels is not limited to this, and may be fixed.
[0034]
As described above, the determination method (color image color classification method) in the case where the black region and the white region exist with the target pixel in between has been described. However, the case where the black region is localized in a predetermined region centered on the target pixel. Can also be performed by the same method.
[0035]
【The invention's effect】
According to the color image color classification method and the color image processing apparatus according to the present invention, the black region is localized within a predetermined region centered on the target pixel, or the black region and the white region exist with the target pixel interposed therebetween. In this case, the target pixel is determined to be a black edge color blur pixel due to color misalignment at the time of scanner input, and is determined to be an achromatic pixel, and attention is paid in the direction from the black region to the opposite non-black region within a predetermined region. Since the surrounding pixels of the target pixel extended by a predetermined number of pixels from the pixel are determined as achromatic, when the larger area including the target pixel is viewed, the size of the line memory necessary for the determination process increases. Without increasing the hardware scale, it is possible to correct chromatic color determination due to color blur such as a black edge with a larger color fringe width to achromatic color determination, and output a scanned original such as a color copier Oite, even if bleeding colors such as black edge when document scanning, it is possible to reproduce them in black monochrome without browned.
[0036]
Further, according to the color image color classification method and the color image processing apparatus according to the present invention, since the achromatic determination is extended in a predetermined direction, if the direction in which the color blur is generated is known, the black edge By limiting the extension of the achromatic determination of the color blur determination pixel only in that direction, the halftone area with low saturation that contains the black component on average, which was previously able to be determined as chromatic, is not erroneously determined as achromatic. Can be.
[0037]
In addition, according to the color image color classification method and the color image processing apparatus according to the present invention, the number of pixels for the extension of achromatic determination is changed according to the magnification of the document. By increasing the number of pixels that extend the achromatic determination of the edge color blur determination pixel, a halftone area with low saturation that includes black components on average, which was previously determined to be chromatic when the scaling ratio is not high, can be obtained. It is possible not to make an achromatic determination accidentally.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of black pixel distribution in a halftone dot portion including black and having low saturation.
FIG. 2 is a diagram illustrating an example of black pixel distribution in a color blur portion of a black edge;
FIG. 3 is a diagram illustrating another example of a black pixel distribution in a black-bleeded portion (a portion in which a black edge is embedded);
FIG. 4 is a block diagram showing an embodiment of the present invention.
FIG. 5 is a block diagram of first determination means.
FIG. 6 is a diagram illustrating a first division pattern of a 5 × 5 pixel region.
FIG. 7 is a diagram illustrating a second division pattern of a 5 × 5 pixel region.
FIG. 8 is a diagram illustrating a third division pattern of a 5 × 5 pixel region.
FIG. 9 is a diagram illustrating a fourth division pattern of a 5 × 5 pixel region.
FIG. 10 is a diagram for explaining an extending direction of achromatic determination according to the present invention.
FIG. 11 is a diagram for explaining achromatic determination of a pixel extended downward by one pixel.
[Explanation of symbols]
1 color conversion unit 2 chromatic / achromatic color determination unit 3 black edge color blur determination unit 3a first determination unit 3b second determination unit 4 correction unit 11-14 counter 15-38 comparator 39-54 AND circuit 55 OR circuit

Claims (6)

In a color image color classification method for determining, for each pixel, a chromatic color and an achromatic color of an input image signal from each component signal of the input color image signal obtained by digitally scanning a color original,
Dividing the predetermined pixel area centered on the target pixel into two symmetrical pixel areas that overlap and include one column of pixels including the target pixel ,
At least one of the bisected pixel regions is determined to be a black region including a black component equal to or greater than the first threshold, and the black component of the black region and the black component of the other pixel region facing each other If the ratio is less than or equal to the second threshold,
Alternatively, when at least one of the bisected areas is determined to be a black area including a black component equal to or greater than the first threshold, and the other facing area is a white area including a white component equal to or greater than the third threshold. ,
The pixel of interest is determined to be a black edge color blur pixel due to color misalignment at the time of scanner input, and determined as an achromatic pixel
Color image color classification method characterized in that a pixel surrounding a target pixel extended by a predetermined number of pixels from the target pixel in a direction from the black region to the opposing non-black region in the predetermined pixel region is determined as achromatic .   2. The color image color classification method according to claim 1, wherein the achromatic determination is extended in a predetermined direction.   3. The color image color classification method according to claim 1, wherein the number of pixels for extending the achromatic determination is changed according to a scaling factor of the document. In a color image processing apparatus that determines, for each pixel, a chromatic color and an achromatic color of an input image signal from each component signal of the input color image signal obtained by digitally scanning a color original.
Dividing the predetermined pixel area centered on the target pixel into two symmetrical pixel areas that overlap and include one column of pixels including the target pixel ,
At least one of the bisected pixel regions is determined to be a black region including a black component equal to or greater than the first threshold, and the black component of the black region and the black component of the other pixel region facing each other If the ratio is less than or equal to the second threshold,
Alternatively, when at least one of the bisected areas is determined to be a black area including a black component equal to or greater than the first threshold, and the other facing area is a white area including a white component equal to or greater than the third threshold. ,
A first determination unit that determines a pixel of interest as a black edge color blur pixel due to color misregistration at the time of scanner input, and confirms the pixel as an achromatic color pixel;
And a second determination unit configured to make achromatic determination of pixels around the target pixel extended by a predetermined number of pixels from the target pixel in a direction from the black region to the opposing non-black region in the predetermined pixel region. A featured color image processing apparatus.   5. The color image processing apparatus according to claim 4, wherein the second determination unit extends the achromatic determination in a predetermined direction.   6. The color image processing apparatus according to claim 4, wherein the second determination unit changes the number of pixels for extension of achromatic determination according to a scaling factor of the document.

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