JP3224172B2 - Color image processing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus for determining a chromatic color or an achromatic color with high accuracy for each pixel of an input color image signal obtained by digitally scanning a color original.

[0002]

2. Description of the Related Art There is a color image processing apparatus for reproducing a black character with a black monochromatic toner by determining a chromatic color and an achromatic color of an input color image signal. In such a color image processing apparatus, for example, a black character detection method (JP-A-2-162966) for detecting black characters by an achromatic color discriminating means, a means for discriminating an achromatic color area, and a chromatic color area are discriminated. Means, and a black character /
There is an apparatus (JP-A-2-249365) for determining a chromatic color area.

[0003]

In each of the above-mentioned techniques, an achromatic color area signal is generated based on the density and saturation of the pixel of interest, and it is determined that the character is a black character or a chromatic color. That is, only black characters with high density are detected as black characters, and black characters with low density are not detected as black characters. For this reason, in a color copying machine or the like, black characters with high density are reproduced with monochromatic black toner, while black characters with low density are reproduced with four color toners of cyan, magenta, yellow, and black. There is a problem that character quality is significantly deteriorated due to toner bleeding or the like.

[0004] Colors of characters, photographs, and halftone dots, which are types of originals, are reproduced by different techniques. For example, as shown in FIG. 9, the halftone dots are reproduced in colors by overprinting dots of cyan, magenta, yellow, and black, and even if they are colors that are close to achromatic or light in appearance,
When a digital signal read and analyzed by a scanner is analyzed, halftone dots remain, and there are large and small chromas in pixel units, and there are large variations.

However, when an achromatic color or a pale color is reproduced in a photograph, the saturation of each pixel is very small and the variation is very small. Also, as noted in the latter gazette, the black character may appear to have a color bleeding (gray balance collapse) around the character when scanned by a scanner, and the black character is determined as a chromatic color. There is a problem that is. Also, in the prior art, the chromatic / achromatic determination criteria are not changed in consideration of the type of the original.
It is difficult to determine achromatic color.

It is an object of the present invention to perform low-density black characters with a single black toner by performing chromatic / achromatic color determination with high accuracy without using a determination unit based on achromatic or black character signals. Chromatic / achromatic color judgment standards are set according to the type of original, and corrections are made according to the chromatic / achromatic color judgment. To provide a color image processing apparatus.

[0007]

According to the first aspect of the present invention, each pixel of an input color image signal obtained by digitally scanning a color original is a chromatic color pixel. Means for determining whether or not the pixel is determined as a chromatic pixel by the determination means in a predetermined local area, and when the count value is equal to or greater than a predetermined value, a pixel of interest at the center of the local area is determined. Means for outputting as chromatic pixels and outputting as achromatic pixels when not.

According to the second aspect of the present invention, means for determining whether each pixel of an input color image signal obtained by digitally scanning a color original is a chromatic pixel, When the pixel determined as a chromatic pixel by the determination unit has a specific pattern, the target pixel at the center of the local region is output as a chromatic pixel,
Otherwise, means for outputting as achromatic pixels is provided.

According to a third aspect of the present invention, the determining means calculates a difference between two primary color signals of different combinations among the three primary color signals of the input color image signal, and determines a maximum value of the difference for each pixel. Each pixel is determined for each pixel, and the maximum value of the difference is compared with a plurality of threshold values, thereby determining whether each pixel is a chromatic pixel or not.

According to the fourth aspect of the present invention, an input color image signal obtained by digitally scanning a color original is divided into three.
Means for calculating a difference between two primary color signals of different combinations among the primary color signals and calculating a maximum value of the difference for each pixel, and comparing the maximum value of the difference with a first threshold value
Is used to determine whether each pixel is a chromatic pixel.
First comparing means, and a maximum value of the difference and a second threshold value.
Is compared to determine whether each pixel is a chromatic pixel.
A second comparing means for determining whether the pixel is determined as a chromatic pixel by the first comparing means in a predetermined local area, and when the counted value is equal to or more than a predetermined threshold value, A first output unit that outputs a pixel of interest at the center of the pixel as a chromatic pixel, and otherwise outputs an achromatic pixel, and a pixel determined as a chromatic pixel by the second comparing unit in a predetermined local area. Outputs a target pixel at the center of the local region as a chromatic pixel when the pixel has a specific pattern, and outputs the pixel as an achromatic pixel when the pixel has no specific pattern.
Means for outputting a logical sum of the output means.

According to a fifth aspect of the present invention, the predetermined threshold value is set according to the color reproduction of a halftone original or a photo original.

[0012]

In the chromatic color area determining means, | RG-, | GB-, and | BR- |
Is calculated, and the maximum value of the difference value is obtained. It is determined whether the pixel is a chromatic pixel (region) or an achromatic pixel (region) by comparing the maximum value of the difference obtained for each pixel with a plurality of thresholds. The correcting means counts the determined chromatic pixels in the local area, and outputs the target pixel as a chromatic pixel when the number is larger than a predetermined number. In other correction means,
When a chromatic pixel has a specific pattern in a local area,
The pixel of interest is a chromatic pixel. In the present invention, in order to reproduce a black character having a low density with a black monochromatic toner, the black character / chromatic color determination, which is the conventional determination criterion, is changed to a chromatic / achromatic color determination. A processing device can be configured. In the present invention,
Since there is no need to provide both the black character determination means and the chromatic color determination means provided in the above-described conventional apparatus, the configuration can be realized with a simple configuration.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the present invention. In the figure, chromatic color area determination means 1
Is the additive or subtractive color method read from the color original.
Of the primary color signals (RGB or ymc), the difference between two colors of different combinations is calculated, the maximum value of the difference is determined for each pixel, and the difference is compared with a threshold to determine whether the pixel is a chromatic pixel (region) or an achromatic pixel. (Area) is determined. The correcting means 2 corrects the chromatic / achromatic pixel determination result determined by the chromatic color area determining means 1. The input image signal has 8 colors.
It is a bit digital signal.

FIG. 2 shows the configuration of the chromatic color area determining means. In the calculation units 11, 12, and 13, | R−G
|, | GB |, | BR− |
In step 5, the maximum value of those differences is obtained. The maximum value of the difference obtained for each pixel is calculated by a plurality of thresholds T by comparators 16 and 17.
is compared with the threshold values ha and Thb, and each comparator outputs “1” when the maximum value of the difference exceeds the threshold value and outputs “0” when the maximum value is equal to or less than the threshold value, thereby determining whether the pixel is a chromatic pixel or an achromatic pixel. .

In this example, the judgment result is output in multiple values,
For example, when there are three comparators that compare the maximum value of the difference with the threshold, a 3-bit determination result is output. In addition, since achromatic colors (white, black, and gray) are in principle R = G = B, the value of the maximum difference value is small. On the other hand, since the maximum difference value of the chromatic color is larger than that of the achromatic color, it is possible to determine whether the pixel is a chromatic pixel or an achromatic pixel by setting the threshold value of the comparator to a predetermined value.

FIG. 3 shows a first embodiment of the correcting means 2. The correction means 2 of the first embodiment takes in the output from one comparator (16 or 17) in FIG. That is, the chromatic / achromatic pixels determined by the chromatic region determining means 1 are sequentially input to the line buffer 21, and the counter circuit 22 counts the chromatic pixels in the local region (for example, 5 × 5 pixels). The value is compared with the threshold value Thc by the comparator 23. When the value is larger than the threshold value, the pixel of interest is output as a chromatic pixel. FIG. 4 shows a 5 × 5 local region and a target pixel.

FIG. 5 shows a second embodiment of the correcting means 2. The correction means 2 of this embodiment also takes in the output from one comparator (16 or 17) as in the first embodiment. In this embodiment, the chromatic pixels determined by the chromatic region determining means 1 are sequentially input to the line buffer 31, and the parameter matching circuit 32 determines the local pixels (for example, 5 × 5 pixels) as shown in FIG. When the pixel has a specific pattern, the pixel of interest at the center of 5 × 5 pixels is output as a chromatic pixel.

The pattern shown in FIG. 6 has a width of at least two pixels when the gray balance collapse around a black character is one pixel width in a scanner with a reading density of 400 dpi. Prepare a pattern to determine. By performing the correction using such a pattern, it is possible to avoid erroneous determination due to the loss of the gray balance around the black character.

For example, as shown in FIG. 7, when a black character "-" is present on a white background, a pixel having a gray balance collapse appears with a width of one pixel. If this determination is corrected by a counting circuit as in the prior art, a black character on a white background may be erroneously determined as a color. On the other hand, in the present embodiment, pattern matching for detecting a chromatic color with a pattern having a width of two pixels is performed, so that a false color pixel (a pixel with an unbalanced gray) around a black character is determined as a chromatic color. Therefore, the black characters on the white background are correctly determined to be achromatic.

FIG. 8 shows the configuration of a second embodiment of the present invention. In the figure, 41 is a circuit for calculating the maximum difference value from the input color image signal, and 42, 44 and 46 are means for comparing the output from the maximum difference calculation circuit 41 with the threshold values Th1, Th2 and Th3 to determine a chromatic color. is there. This circuit 41 and 4
2 (or 41 and 44, 41 and 46) constitutes the chromatic area determination circuit shown in FIG.

Reference numeral 43 denotes a correction unit using the pattern matching shown in FIG. Also, 45 and 47 are each shown in FIG.
Is a counting circuit shown in FIG. Here, the circuits 42 and 43 are used as means for detecting the color of the character portion, and the threshold Th1 of the circuit 42 uses a small value. Circuits 44 and 4
5 is used as a means for detecting the color of a halftone dot, a relatively large value is used for the threshold value Th2 of 44, and a threshold value Th4
Uses a small value such as 1 or 2.

Reference numerals 46 and 47 are used as means for detecting the color of a photograph. A small value is used for the threshold value Th3 of 46, and a large value is used for the threshold value Th5 of 47. For example, 5
When counting within a local area of × 5 pixels, a value of 20 or more is used. After determining the chromatic / achromatic color of a character, a halftone dot, and a photograph by the above-described circuits, a logical sum is obtained by a logical sum circuit 48 to obtain a final chromatic / achromatic color output.

[0023]

As described above, claims 1 and 2,
According to the invention described in (3), (1) the chromatic / achromatic color determination is performed only by the chromatic color determination. In other words, since the black character determination means is not provided, the configuration is simpler than the conventional device. In addition, even a black character having a low density can be reproduced with high image quality in a single black color. (2) letters, photos,
Since the chromatic color determination standard is set in accordance with the color reproduction method of each original document with halftone dots, chromatic / achromatic color determination can be performed with high accuracy for various original documents. (3) Since the signal obtained from the scanner can be used as it is, it can be realized with a simple configuration. (4) Since the correction is performed by counting the frequency of the chromatic / achromatic color determination pixel, the chromatic / achromatic color determination of a photograph or a halftone dot can be performed with high accuracy. (5) Since pattern matching is performed by preparing a pattern corresponding to the characteristic of gray balance collapse around black characters, the gray balance collapse around black characters is not determined to be chromatic.
Chromatic / achromatic color determination can be performed with high accuracy.

According to the fourth and fifth aspects of the present invention, (6)
Since different chromatic color judgment standards and correction methods are provided, originals with different color reproduction of characters, photographs,
Achromatic color determination can be performed with higher accuracy. (7) Since the optimum chromatic color criterion and correction method can be selected according to the color reproduction method of the text, photograph, and halftone originals, the chromatic / achromatic judgment of various originals can be performed with higher accuracy. .

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 shows a configuration of a chromatic color area determination unit.

FIG. 3 shows a first embodiment of the correction means.

FIG. 4 shows a local region of 5 × 5 size and a pixel of interest.

FIG. 5 shows a second embodiment of the correction means.

FIG. 6 shows a pattern for determining a chromatic color.

FIG. 7 is a diagram illustrating a gray balance breakdown of a black character “-”.

FIG. 8 shows a configuration of a second exemplary embodiment of the present invention.

FIG. 9 is a diagram illustrating color reproduction of a halftone dot document.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Chromatic area determination means 2 Correction means 11, 12, 13 Computing units 14, 15, 16, 17 Comparator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (5)

(57) [Claims] 1. A means for determining whether each pixel of an input color image signal obtained by digitally scanning a color document is a chromatic pixel, and a determination means for determining whether or not each pixel is a chromatic pixel in a predetermined local area. Means for counting pixels determined to be chromatic pixels, outputting the pixel of interest at the center of the local region as a chromatic pixel when the counted value is equal to or greater than a predetermined value, and outputting the pixel of interest as an achromatic pixel otherwise. A color image processing apparatus. 2. A means for judging whether or not each pixel of an input color image signal obtained by digitally scanning a color original is a chromatic pixel, and means for judging whether or not each pixel is a chromatic pixel in a predetermined local area. Means for outputting the pixel of interest at the center of the local area as a chromatic pixel when the pixel determined to be a chromatic pixel has a specific pattern, and outputting the pixel of interest as an achromatic pixel otherwise. Color image processing device. 3. The determination means calculates a difference between two primary color signals of different combinations among the three primary color signals of the input color image signal, obtains a maximum value of the difference for each pixel, and 3. The color image processing apparatus according to claim 1, wherein a multi-value determination is performed as to whether each pixel is a chromatic pixel by comparing the maximum value of with a plurality of threshold values. 4. A method for calculating a difference between two primary color signals of different combinations among three primary color signals of an input color image signal obtained by digitally scanning a color original and calculating the maximum value of the difference for each pixel. Means for calculating each difference,
By comparing the large value with the first threshold, each pixel has
First comparing means for determining whether or not the pixel is a colored pixel;
By comparing the maximum value of the difference with the second threshold value,
Second comparison to determine whether each pixel is a chromatic pixel
Means for counting pixels determined as chromatic pixels by the first comparing means in a predetermined local area, and when the counted value is equal to or greater than a predetermined threshold, the pixel of interest at the center of the local area is chromatic. A first output unit that outputs as a pixel, otherwise outputs as an achromatic pixel, and a pixel determined as a chromatic pixel by the second comparing unit in a predetermined local area has a specific pattern. A second output unit that outputs a pixel of interest at the center of the local region as a chromatic pixel, and otherwise outputs an achromatic pixel, and outputs a logical sum of the first output unit and the second output unit And a color image processing apparatus. 5. The color image processing apparatus according to claim 4, wherein said predetermined threshold value is set according to color reproduction of a halftone original and a photo original.