JPH0548892A - Color picture processor - Google Patents

Abstract

PURPOSE:To separate a black character area, color character area, and drawing area from a color original, to operate a processing for block characters to the black character area, to operate a reproducing processing to the color character area by the identified color of the character, and to operate a drawing processing to the drawing area by three or four colors. CONSTITUTION:A synthetic judging circuit 12 judges the character area and the drawing area by outputs of a color judging circuit 11 and a character detecting circuit 10. A UCR circuit 5 selects a UCR processing for the character area or that for the drawing area by the judged result of a line 13. A selecting circuit 8 selects a signal binarized by a dither circuit 6 in the case of the drawing area, selects a signal K4b outputted by a binarizing means 7 in the case of the black character area, selects the signal of the judged color in the case of the color character a tea by the judged output of a line 14, and outputs it to a color printer.

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 digitally reproducing a color image from a color original, and particularly to separating a black character area, a color character area and a picture area from the color original, and for each area. The present invention relates to a color image processing device that performs optimum color processing.

[0002]

2. Description of the Related Art For example, in the case of a color copier, black characters in a document are preferably reproduced in a single black color in order to improve reproduction image quality and reduce ink consumption.
Therefore, for example, the minimum signal MIN (Y, M, C) of each color signal of Y (yellow), M (magenta), and C (cyan) after color correction (masking) of color image data is equal to or more than a predetermined threshold value. It is sufficient to reproduce the image by the black monochromatic process without applying the inks of Y, M, and C to the image area. However, in the case of a manuscript in which pictures (halftone images, photographic images) and characters are mixed, not only black characters but also the picture parts are often subjected to black monochromatic processing, and a desirable halftone expression cannot be obtained and reproduced. The image quality deteriorates. Appropriate undercolor removal processing, UCR (Under Col)
or Removal) processing (for example, 50% UCR processing) is preferable in terms of image quality.

As an apparatus for reproducing only black characters from a color original in a single black color, Japanese Patent Laid-Open No. 63-2401 has been disclosed.
There is a color image forming apparatus described in Japanese Patent No. 75. In this apparatus, a character area extracting means utilizing the continuity of pixels of character edges and Y, M, C after color correction
There is a means for detecting black from the minimum signal MIN (Y, M, C) in the signal, and the black character area is separated by the logical product of the detection results of each means and black monochromatic processing is performed.

[0004]

However, depending on the black character area separating means, halftone dots which are black and have dot-like continuous area ratios of around 50% are erroneously determined to be black characters. , Y, M, C for color halftone images
There are scattered linear or rod-shaped portions of the ink, but this portion is also erroneously determined as a black character area, and as a result, the reproduced image quality is significantly deteriorated. Further, since the color letters are also subjected to the pattern processing, there is a problem that the resolution of the letters is lost.

Also, a document such as a newspaper containing a mixture of black and white halftone dot images (for example, 60 lines) having a relatively low number of lines is 400
When inputting with a scanner of about dpi, it is difficult to sufficiently remove the halftone dot pattern even with a smoothing filter for removing moire, which is set with a high number of lines. The image quality is improved when the halftone dot shape of the original is positively reproduced by performing the character processing and the black ink alone is output. In addition, even in newspaper manuscripts, the color halftone photo area has a relatively high number of lines (for example, about 100 lines),
In order to reproduce the color halftone dot satisfactorily, it is desirable to perform smoothing and color pattern processing.

An object of the present invention is to separate a black character area, a color character area, and a picture area from a color original document, perform black character processing on the black character area, and determine the determined character of the color character area. The color is reproduced, and Y is applied to the picture area.
Another object of the present invention is to provide a color image processing apparatus that performs pattern processing with three colors of M and C or four colors of Y, M, C and Bk. Another object of the present invention is to separate a black character region, a black pattern region, a color character region, and a color pattern region from a color original document, perform black monochromatic processing on the black character region and the black pattern region, and Is to provide a color image processing apparatus in which reproduction processing is performed in a character color, pattern processing is performed in three or four colors for a pattern area, and image quality is improved for a low line number original such as a newspaper. ..

[0007]

In order to achieve the above object, according to the invention of claim 1, a color original is digitally read, and yellow, magenta, cyan and black inks are read from the read color image data. In a color image processing apparatus for digitally reproducing a color image using the means, means for separating the color original data into a character area and a picture area, means for determining a color of a local area in the color original data, The color original data is divided into a black character area, a color character area, and a picture area according to the output of the separating means and the color determining means, and the black character area is reproduced in a single black color. The character area is reproduced in the determined color, and the pattern area is processed in four colors of yellow, magenta, cyan and black.

According to the second aspect of the present invention, a color image processing for digitally reading a color original document and digitally reproducing a color image from the read color image data using yellow, magenta, cyan and black inks is performed. In the apparatus, means for separating the color original data into a character area and a pattern area, means for determining a color of a local area in the color original data, and means for separating the color original data according to outputs from the separating means and the color determining means. Means for separating the image area of the color manuscript data into a black character area, a black picture area, a color character area and a color picture area, the black character area and the black picture area are reproduced in a single black color, and the color character area is judged as described above. Reproduction processing in the specified color,
The pattern area is characterized in that pattern processing is performed with four colors of yellow, magenta, cyan, and black.

According to a third aspect of the present invention, the means for separating the color original data into a character area and a picture area is characterized by performing separation processing using the G signal in the color original data.

According to the fourth aspect of the present invention, a color image processing for digitally reading a color original and digitally reproducing a color image from the read color image data using yellow, magenta, cyan and black inks is performed. In the apparatus, means for determining the presence / absence of a color in a local area in color original data, means for processing black characters in an uncolored area in accordance with the output of the determining means, and color processing for a colored area And a means for processing a pattern.

[0011]

The image area separating means judges the character area and the picture area by the outputs from the color judging means and the character detecting means, and the UCR
The circuit is instructed to perform the UCR processing A for the character area or the UCR processing B for the picture area, and to the selection circuit, in the case of the picture area, the binarized signal C4 by the dither circuit.
Instruct to select a, M4a, Y4a, K4a,
In the case of a black character area, the signal K4b output from the binarization circuit
In the case of a color character, it is instructed to select the signal of the determined color. As a result, the black character area is reproduced (printed) in a single black color by the color printer, and the color character area is reproduced in any of the determined eight colors (cyan color,
It is printed in red, etc., and in the case of the pattern area,
The pattern is processed by three colors of Y, M, C or four colors of Y, M, C, Bk.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a block diagram of the first embodiment of the present invention. The input sensor 1 has a photoelectric conversion element such as a CCD camera, and reads a color original to read R (red),
The color separation signals of three colors G (green) and B (blue) are output. A
The / D converter 2 converts the R, G, B signals into, for example, an 8-bit digital signal. The log converter 3 uses R,
The density of G and B digital signals is converted to C (cyan), M
Signals C1, M1, and Y1 representing the amounts of the respective inks of (magenta) and Y (yellow) are output. Masking circuit 4
In order to remove the turbid component of the color separation filter of the input sensor 1 and the turbid component of the ink, the C1, M1, and Y1 signals are color-corrected (masked), and the C2, M2, and Y2 signals are output.

This color correction is based on the following equation, for example. Y2 = K11 × Y1 + K12 × M1 + K13 × C1 M2 = K21 × Y1 + K22 × M1 + K23 × C1 C2 = K31 × Y1 + K32 × M1 + K33 × C1 (K11 to K33 are constants determined by experiment)

The UCR circuit 5 is a circuit for performing undercolor removal processing (UCR processing), and represents C2, M2, and
C of Y2 signal with some or all removed
3, M3, Y3 signals and black ink signal K corresponding to the removal amount
3 is generated. Here, UCR processing A (character area processing) and UCR processing B (pattern area processing) can be selected as the UCR processing.

The UCR processing A for character areas generates a K3 signal for black characters, and C3 and K3 for cyan characters.
Generate a signal. In the example of UCR 100% in black characters, when Y2, M2, and C2 signals having the values shown in FIG.
The amount of 100% of the IN (C2, M2, Y2) signal is C2.
The values subtracted from the M2, Y2 signals are C3, M3, Y3, and K3 is the value of MIN (C2, M2, Y2), that is, Y.
2 (Fig. 3). Similarly, cyan character UCR100
In the example of%, when the Y2, M2 and C2 signals having the values shown in FIG. 4 are input, the C3, M3 and K3 signals having the values shown in FIG. 5 are generated.

The UCR process B for the picture area is MIN (C
2, M2, Y2), for example, 50% of the amount of C2, M2
2, the value subtracted from the Y2 signal becomes C3, M3, Y3,
K3 is so-called 50% UCR processing for generating a signal having a value of MIN (C2, M2, Y2). In the case of the input data shown in FIG. 6, C3, M3, Y having the values shown in FIG.
3, K3 signal is generated.

A UCR process A for character areas is selected for a pixel area determined to be a character and a pixel area determined to be a pattern is used for a pattern area by a control signal from a comprehensive determination circuit 12 described later. Select UCR process B. The dither circuit 6 is a circuit that binarizes the C3, M3, Y3, and K3 signals by the systematic dither method, and its output signals C4a, M4a, Y4a, and K4a are input to the selection circuit 8. The binarization circuit 7 is a circuit that binarizes the C3, M3, Y3, and K3 signals with a predetermined threshold value. The signals C4b, M4b, Y4b, and K4b output by the binarization circuit are selected by the selection circuit 8 respectively. Entered in.

The selection circuit 8 is a comprehensive judgment circuit 12 which will be described later.
For the pixel area determined to belong to the picture area by the control signal from the signal C from the signal C output from the dither circuit 6.
4a, M4a, Y4a, K4a are selected, and the binarization circuit 7 is applied to the pixel area determined to be the pixel belonging to the black character.
The signal K4b output by the binarizing circuit 7 is selected, and the pixel C4b output by the binarization circuit 7 is selected for the pixel belonging to the color character area, for example, the pixel area determined to be a cyan character. In the color printer 9, receiving the signal from the selection circuit 8,
A color image is reproduced by turning on / off the ink dots of each color.

The character detection circuit 10 is a circuit for extracting a character area on a color original document. The character detection circuit 10 outputs R, G, B signals output from the scanner (αR + βG + γB signals obtained by linearly combining these signals, or max (R,
G, B) signal) or Y, M, C representing the amount of ink
Any one of the signals (αY + βM + γC signals obtained by linearly combining them, or max (Y, M, C) signals) is input.
Here, α, β and γ are coefficients, which are determined by experiments or the like. In this embodiment, αY2 + after the masking process is performed.
From the βM2 + γC2 signal, a pixel area in which a part of a character and a part of a white background continuous with the character coexist is detected.

FIG. 8 is a diagram showing a specific configuration of the character detection circuit 10 (note that such a character detection circuit has already been proposed by the applicant as Japanese Patent Application No. 2-118358). .. Character detection is performed as follows. That is, the binarization circuit 31 causes the MIN (C2, M2,
The Y2) signal is binarized into a low level / non-low level by a predetermined threshold value and then input to the low level pixel pattern matching circuit 32. In this circuit 32, for example, the low level /
When the non-low level pattern matches any of the patterns shown in FIG. 9, the pixel of interest is determined to be a character low level pixel, and "1" is output. The counting circuit 33 counts the number of “1” outputs of the low-level pixel pattern matching circuit 32, that is, the number of character low-level pixels in, for example, a 3 × 3 matrix centered on the pixel of interest, and the count value is a constant value ( For example, in the case of 2) or more, "1" is output.

Further, the binarization circuit 34 causes C2, M
2, which is the maximum signal of the Y2 signals, MAX (C2, M2,
The Y2) signal is binarized into a high level / non-high level by a predetermined threshold value and then input to the high level pixel pattern matching circuit 35. In this circuit 35, for example, the high level /
When the non-high level pattern matches any of the patterns shown in FIG. 10, the pixel of interest is determined to be the character high level pixel, and "1" is output. The counting circuit 36 counts the number of character high level pixels from the output of the high level pixel pattern matching circuit 35, for example, in a 3 × 3 matrix centered on the pixel of interest, and the counted value is a fixed value (for example, 2) or more. At the time of, "1" is output.

The AND circuit 37 outputs a logical product signal of the output signals of the counting circuits 33 and 36. That is, if, for example, two or more character low-level pixels and two or more character high-level pixels simultaneously exist in a 3 × 3 matrix centered on the pixel of interest, the AND circuit 37 outputs "1". At this time, this pixel of interest is defined as a temporary character pixel.

The determination circuit 38, for example, if the temporary character pixels are a certain number or more in a 5 × 5 matrix centered on the pixel of interest, the pixel of interest or a block of a certain size (5 × 5) including the pixel of interest. Matrix is determined to be a character area, and "1" is output. That is, the character area is extracted by utilizing the property that the connected high-level pixels and the connected low-level pixels simultaneously exist at a certain density or more in the contour portion of the character.

Further, in order to improve the character detection accuracy, it is also possible to use a halftone dot area separation technique (Japanese Patent Application No. 2-75466) and a white background detection technique (Japanese Patent Application No. 1-271987).

The color determination circuit 11 is a circuit for determining the color of the pixel of interest or the block of interest, and is C2 of the pixel of interest.
The M2 and Y2 data are binarized by predetermined threshold values, for example, C2> threshold value c, M2> threshold value m, Y2> threshold value y, black, C2 ≦ threshold value c, M2> threshold value m, Y2> threshold value. If y, red, C2> threshold c, M2 ≦ threshold m, Y
If 2 ≦ threshold value y, it is determined that the color is cyan. In this case, there are eight types of colors. In the case of the block of interest, the average is taken for each of C, M, and Y in the block, and then binarized by a predetermined threshold to determine the color.

The comprehensive judgment circuit 12 judges the character area and the picture area based on the outputs from the color judgment circuit 11 and the character detection circuit 10, and the UCR circuit 5 for the character area or the UCR processing A for the character area is performed to the UCR circuit 5 through the line 13. The UCR process B for the picture area is instructed, and signals C4a, M4a, Y4a, K for the picture area are sent to the selection circuit 8 via the line 14.
4a is selected, and the signal K4b is selected in the case of a black character area, and the signal of the determined color is selected in the case of a color character.

Therefore, the black character area is the color printer 9
Is reproduced (printed) in a single black color, and the color character area is any of the eight judged colors (cyan, red, etc.)
Printed by. For the picture area, Y, M,
The pattern is processed by three colors of C or four colors of Y, M, C and Bk.

(Embodiment 2) FIG. 11 is a block diagram according to the second embodiment. The difference from Embodiment 1 is that a mode setting unit 15 is provided and the character detection circuit 101 is G
The point is that characters and patterns are separated only from the (green) signal. In the present embodiment, as described above, the image quality is particularly improved for a printed document with a low number of lines such as a newspaper. For example, the "newspaper document mode" is set in the mode setting unit 15 by the operator.

By the mode setting, the comprehensive judgment circuit 12
1 is black character processing is performed on a region which is determined to be a character and has no color and a region which is determined to be a pattern (halftone dot) and has no color and is a character and has color. Color character processing is applied to the area that is determined to be a pattern (dot)
Therefore, for the area determined to have a color, through the lines 13 and 14, the color pattern processing is performed.
Instruct the UCR circuit 5 and the selection circuit 8. FIG. 12 is a diagram showing the determination result of the image area separation and the processing content.

As described above, according to the present embodiment, even in the case of a picture character mixture image including a low frequency halftone dot area such as a newspaper,
Optimal output processing for each area, that is, the black dot area and the black character area are character-processed with black ink, and the color character area is character-processed with color ink,
Since the color dot area is dithered with color ink,
Playback image quality is improved.

As described above, the character detection circuit 101 of this embodiment separates characters and patterns from only the G (green) signal, so that the hardware amount of the character detection circuit is that of the first embodiment. Compared to 1/3. Hereinafter, when separating characters and patterns, a G (green) signal (or M2 after color correction)
The reason for using (signal) will be described.

The object of separating the character portion is limited to the character on the white background. In other words, it is sufficient to know whether or not there is a coloring material on the white background, so the following three separation methods are possible. R,
Separation processing is performed on each data of G, B (or Y, M, C after color correction), and the logical sum of the results is obtained. R,
The maximum value of G and B data is calculated, and the separation processing is performed using the data. Lightness is calculated from R, G, B data,
Separation processing is performed using the data. The above method
Since data of 3 systems of R, G, B (or Y, M, C) is used, the amount of hardware increases, and R,
Since the positional accuracy of G and B is not perfect, the data calculated in the above step is not suitable as the data used for the separation process because the edge portion of the image is blunted.

Therefore, if separation processing is performed using any one of R, G, and B systems, the hardware amount is reduced to 1/3 and the edge portion is not sagging. Now, the reason why G data is used in this embodiment when performing separation processing using one system of data will be described in detail. Before that, separation performance when color separation data is used for separation processing will be described. FIG. 13 shows the spectral reflection characteristics of the coloring material.
[Fig. 4] is a diagram showing absorption amounts (concentrations) of R, G, and B lights of respective color materials.

As is clear from FIG. 13, Y (yellow)
Has a near-ideal spectral characteristic, while C (cyan) and M
The spectral characteristics of (magenta) have a large deviation from the ideal.
That is, the actual C spectral characteristic has absorption in the G wavelength range, and similarly, the actual M spectral characteristic has absorption in the B wavelength range. Further, as is clear from the density values in FIG. 14, the absorption amount of R and G light for Y ink is very small, but the absorption amount of G light for C ink and the absorption amount of B light for M ink are large. ..

Therefore, when the C character is separated by using the G data, there should be no absorption of G light because there is originally no M component, but in reality, the C ink contains a considerable amount of M component. Therefore, there is absorption of G light, and the C character can be detected. FIG. 15 shows the representative seven colors, the color materials used to represent the colors, and the separation possibility when the separation is performed using the R, G, and B color separation data.
It is the figure represented by (DELTA). In this figure, ◯ is separable (absorption occurs), × is non-separable (absorption does not occur), Δ is not separable with an ideal coloring material, but actual color It shows that the materials can be separated according to their spectral characteristics.

As is apparent from FIG. 15, when the separation processing is performed using the G data, the color that cannot be detected is the Y color. However, as a human visual characteristic for Y characters on a white background, the resolution performance is low, so even if separation processing and high resolution processing are applied to the character portion, the effect is more prominent than other colors. Absent. Therefore, as in the present embodiment, even if only one system of G data is used, the separation processing can be practically performed without any trouble.

(Third Embodiment) FIG. 16 is a block diagram of the third embodiment. The difference from the first and second embodiments is that the character detection circuit and the comprehensive judgment circuit are not provided and the binarization is performed. In the circuit 71, only black is processed. That is, the present embodiment is particularly effective when applied to a character halftone dot manuscript having a relatively low number of lines such as a newspaper as an input manuscript, and is realized by only a simple color judgment circuit. Compared to 2, the amount of hardware is significantly reduced.

The color determination circuit 111 instructs the UCR circuit 5 to select the signal K3 via the line 13 for the area determined to have no color, whereby the binarization circuit 71 processes the black character. The selection circuit 8 is connected to the line 1
The output of the binarization circuit 71 is selected by an instruction signal via 4 and sent to the color printer 9. On the other hand, for the area determined to have color, the output of the UCR circuit 5 is subjected to pattern processing by the dither circuit 6 by an instruction signal via the line 13 and sent to the color printer 9 via the selection circuit 8.
FIG. 17 is a diagram showing a color determination result and processing contents corresponding thereto.

As described above, according to the present embodiment, by the judgment of the color judgment circuit, it is possible to carry out the processing suitable for the picture / character mixed image including the halftone dot area having a relatively low number of lines such as a newspaper. That is, the black dot area and the black character area are character-processed with black ink, and the color character area and the color dot area are dithered with color ink, so that a high-quality image can be output. It should be noted that it is desirable to perform color character processing on the color character area, but since color characters in newspapers are often relatively thick in general, even simple processing as in this embodiment has a great effect of improving image quality. ..

[0040]

As described above, according to the invention described in claim 1, since the black character area, the color character area, and the picture area are accurately separated from the color original, a black character is generated for a black character. Processing is performed and the color characters are reproduced in the determined color, so the deterioration of resolution due to the pattern processing of color characters, which has been a problem in the past, can be eliminated and the reproduction image quality can be greatly improved. There is an effect that can be. According to the second aspect of the present invention, even for an original image including a halftone dot area having a low number of lines, such as a newspaper, the optimum processing is performed for each area, so that the reproduced image quality is improved. According to the third aspect of the present invention, since the character and the pattern are separated from only the G signal, the amount of hardware of the character detection circuit can be reduced. According to the invention described in claim 4, since it is composed of a simple color judgment circuit, the amount of hardware is significantly reduced, and when it is applied to a character halftone dot original having a relatively low number of lines such as a newspaper, a remarkable effect is obtained. There is.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating a black character before UCR processing.

FIG. 3 is a diagram for explaining after 100% UCR processing of black characters.

FIG. 4 is a diagram illustrating a cyan character before UCR processing.

FIG. 5 is a diagram for explaining after 100% UCR processing of cyan characters.

FIG. 6 is a diagram illustrating a UCR process before a pattern area.

FIG. 7 is a diagram for explaining after 50% UCR processing of a pattern area.

FIG. 8 is a block diagram showing an example of a character detection circuit.

FIG. 9 is a diagram showing a pattern for character detection.

FIG. 10 is a diagram showing another pattern for character detection.

FIG. 11 is a block configuration diagram according to a second embodiment of the present invention.

FIG. 12 is a diagram illustrating a determination result of image area separation and processing contents.

FIG. 13 is a diagram showing a spectral reflection characteristic of a coloring material.

FIG. 14 is a diagram showing absorption amounts (concentrations) of R, G, and B lights of respective color materials.

FIG. 15: Representative seven colors and their color materials, and R, G, B
It is a figure showing the possibility of separation when performing separation using each color separation data of.

FIG. 16 is a block configuration diagram according to a third embodiment of the present invention.

FIG. 17 is a diagram showing a color determination result and processing contents corresponding thereto.

[Explanation of symbols]

 1 Input Sensor 2 A / D Converter 3 Log Conversion Circuit 4 Masking Circuit 5 UCR Circuit 6 Dither Circuit 7, 71 Binarization Circuit 8 Selection Circuit 9 Color Printer 10, 101 Character Detection Circuit 11, 111 Color Judgment Circuit 12, 121 Comprehensive judgment circuit 15 Mode setting section

Claims (4)

[Claims] 1. A color original is digitally read, and yellow, magenta, and
In a color image processing apparatus which digitally reproduces a color image using cyan and black inks, a means for separating the color original data into a character area and a pattern area, and a color of a local area in the color original data are displayed. And a means for separating the color manuscript data into a black character area, a color character area, and a picture area according to the outputs of the separating means and the color judging means. A color image processing apparatus, wherein reproduction processing is performed, the color character area is reproduced with the determined color, and the pattern area is processed with four colors of yellow, magenta, cyan, and black. 2. A color original is digitally read, and yellow, magenta, and
In a color image processing apparatus which digitally reproduces a color image using cyan and black inks, a means for separating the color original data into a character area and a pattern area, and a color of a local area in the color original data are displayed. And a means for separating the color manuscript data into a black character area, a black picture area, a color character area and a color picture area according to the outputs of the separating means and the color judging means. The area and the black pattern area are reproduced with a single black color, the color character area is reproduced with the determined color, the pattern area is yellow,
A color image processing device characterized by performing pattern processing with four colors of magenta, cyan, and black. 3. The color image processing apparatus according to claim 2, wherein the means for separating the color original data into a character area and a picture area performs separation processing using a G signal in the color original data. 4. A color original is digitally read, and yellow, magenta, and
In a color image processing apparatus that digitally reproduces a color image using cyan and black inks, a unit that determines the presence or absence of a color in a local area in color original data, and a color that is output according to the output of the determination unit. A color image processing apparatus comprising: means for processing black characters in a non-colored area; and means for processing a color pattern in a colored area.