JP2856867B2 - Color image processing equipment - Google Patents

Description

Description: 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 more particularly, to a color image processing apparatus for performing black monochromatic processing inside black characters. About.

(Prior art)

For example, in the case of a color copier, it is preferable that black characters in a document be 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 the color image data is equal to or larger than a predetermined threshold. The image may be reproduced by black single-color processing without applying Y, M, and C inks to the image area.
However, in the case of a document in which a pattern (halftone image, photographic image) and characters are mixed, not only black characters but also the pattern portion are frequently subjected to black monochromatic processing, and a preferable halftone expression is not obtained. Image quality deteriorates. For a pattern, an appropriate under color removal process, so-called UCR (Under Color Rem
oval) processing (eg, 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, there is a color image forming apparatus described in JP-A-63-240175. In this apparatus, a character area extracting means utilizing the continuity of pixels of a character edge and a minimum signal MIN among Y, M, and C signals after color correction are provided.
There is a means for detecting black from (Y, M, C), and a black character area is separated by a logical product of detection results of the respective means to perform black monochromatic processing.

Further, the present applicant has already proposed a color image processing apparatus that detects black characters from a color image and reproduces the black characters in a single black color (for example, Japanese Patent Application No. 2-118358).

[Problems to be solved by the invention]

However, in the above-described technique, since the region separated as a black character is the edge portion of the black character as shown in FIG. 8, the inside of the black character is subjected to pattern processing, and Y, M, C, and Bk are processed.
There is a disadvantage in that the amount of ink consumption increases because the image is reproduced with the color ink.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image processing apparatus that performs black monochrome processing even inside a black character.

[Means for solving the problem]

In order to achieve the above object, according to the first aspect of the present invention, a color original is digitally read, and multicolor superimposition is performed using yellow, magenta, cyan, and black color materials based on the read color image data. A color image processing apparatus that reproduces a color image by: a character detection unit that detects whether a target pixel of the color image data is a character region; a color determination unit that determines a color of the target pixel; Determining means for determining the target pixel into a black character area and a picture area based on the detection result of the character detecting means and the determination result of the color determining means; When being surrounded by an area, means for changing the determination of the first pixel of interest to a black character area and means for reproducing the determined black character area in a single black color are provided.

(Operation)

A character area and a picture area are determined based on outputs from the color determination circuit and the character detection circuit. When the pixel of interest belonging to the minute picture area is surrounded by a black character area, the determination correction circuit determines that the pixel of interest is a black character area. Therefore, the black character area is printed with a single black color by a color printer. As a result, not only the edge of the black character but also the inside thereof is reproduced in a single black color, so that the reproduced image quality is improved, and at the same time, the ink consumption can be reduced.

Embodiment An embodiment of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The input sensor 1 has a photoelectric conversion element such as a CCD camera or the like, and reads a color original to read R (red), G (green) B
The color separation signals of three colors (blue) are output. A / D converter 2
Converts the R, G, B signals into, for example, 8-bit digital signals. The log converter 3 converts the density of the R, G, and B digital signals into C (cyan), M (magenta), and Y
The signals C1, M1, and Y1 representing the amounts of the respective color inks (yellow) are output. The masking circuit 4 corrects (masks) the C1, M1, and Y1 signals in order to remove the turbid component of the color separation filter of the input sensor 1 and the turbid component of the ink.
2. Output Y2 signal. This color correction is based on, for example, the following equation.

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 experiments) UCR circuits 5 and 6 are undercolor A circuit that performs removal processing (UCR processing). For C2, M2, and Y2 signals that represent the amount of ink,
The C3, M3, and Y3 signals from which some or all of the signals have been removed and the black ink signal K3 corresponding to the removed amount are generated.

The UCR circuit 5 for the character area generates a black ink signal K3a = MIN (C2, M2, Y2) for a black character. UCR1 in black letters
In the example of 00%, when the Y2, M2, and C2 signals having the values shown in FIG. 2A are input, the amount of 100% of the MIN (C2, M2, Y2) signal is set to C
The value subtracted from the 2, M2, Y2 signal is C3a, M3a, Y3a, and K3a is M
The value of IN (C2, M2, Y2), that is, Y2 (FIG. 2 (b)). Similarly, in the example of cyan character UCR 100%, when the Y2, M2, and C2 signals having the values shown in FIG.
The C3a, M3a, and K3a signals having the values shown in FIG. 2D are generated.

The UCR circuit 6 for the picture area is obtained by subtracting, for example, the amount of 50% of the MIN (C2, M2, Y2) signal from the C2, M2, Y2 signal to obtain the value of C3b, M3b, Y3.
b, and K3b is a so-called 50% UCR process that generates a signal having a value of MIN (C2, M2, Y2). In the case of the input data shown in FIG. C3b,
M3b, Y3b and K3b signals are generated.

The binarization circuit 7 is a circuit that binarizes the C3a, M3a, Y3a, and K3a signals with a predetermined threshold value. The signals C4a, C4a, Y4a, and K4a output from the binarization circuit are selected by a selection circuit 9 respectively. Is input to

The dither circuit 8 is a circuit that binarizes the C3b, M3b, Y3b, and K3b signals by an organized dither method, and outputs an output signal C4.
b, M4b, Y4b, and K4b are input to the selection circuit 9.

The selection circuit 9 outputs signals C4b, M4b, Y4b, and K4 output from the dither circuit 8 for a pixel area determined to belong to the picture area by a control signal from a determination correction circuit 14 described later.
4b is selected, and for a pixel area determined to belong to a black character area, a signal K4a output by the binarization circuit 7 is selected, and for a pixel belonging to a color character area, for example, a pixel area determined to be a cyan character Selects the signal C4a output from the binarization circuit 7.

The color printer 10 receives a signal from the selection circuit 9 and reproduces a color image by turning on / off the ink dots of each color.

The character detection circuit 11 is a circuit for extracting a character area on a color document. The character detection circuit 11 outputs R, G, B signals (αR + β obtained by linearly combining them) output from the scanner.
G + γB signal or max (R, G, B) signal) or Y, M, C signals representing the amount of ink (αY + βM + γC signal obtained by linearly combining them, or max (Y, M, C) signal) Enter Here, α, β, and γ are coefficients, which are determined by experiments or the like.

In this embodiment, αY2 + βM2 + γ after the masking process
From the C2 signal, a pixel region where a part of a character and a part of a white background continuous with the character coexist is detected.

FIG. 3 is a diagram showing a specific configuration of the character detection circuit 11 (note that such a character detection circuit has already been proposed by the present applicant as Japanese Patent Application No. 2-118358). Detection is performed as follows. That is, the binarization circuit
At 31, the MIN (C2, M2, Y2) signal is binarized to a low level / non-low level by a predetermined threshold and then input to the low-level pixel pattern matching circuit 32. In this circuit 32, for example, when a low-level / non-low-level pattern in a 3 × 3 matrix with the target pixel as the center pixel matches any of the patterns shown in FIG. And outputs “1”. 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, for example, in a 3 × 3 matrix centered on the pixel of interest, and the counted value is a constant value ( For example, "1" is output at the time of 2) or more.

Further, the binarization circuit 34 binarizes the MAX (C2, M2, Y2) signal, which is the maximum signal among the C2, M2, Y2 signals, into a high level / non-high level by a predetermined threshold, and then converts the signal to a high level. It is input to the pixel pattern matching circuit 35. In this circuit 35, for example, when a high-level / non-high-level pattern in a 3 × 3 matrix with the target pixel as the center pixel matches any of the patterns shown in FIG. And outputs “1”. The counting circuit 36 counts the number of character high-level pixels in, for example, a 3 × 3 matrix centered on the pixel of interest, for example, from the output of the high-level pixel pattern matching circuit 35, and the counted value is equal to or more than a certain value (for example, 2) Outputs “1” when.

The AND circuit 37 outputs an AND signal of the output signals of the counting circuits 33 and 36. That is, 3 × 3 around the pixel of interest
For example, if two or more character low-level pixels and two or more character high-level pixels exist simultaneously in the matrix of
The AND circuit 37 outputs “1”. At this time, the target pixel is set as a provisional character pixel.

For example, if the number of temporary character pixels is equal to or more than a predetermined number in a 5 × 5 matrix centered on the target pixel, the determination circuit 38 determines the target pixel or a block of a certain size including the target pixel (5 × 5 matrix). Is determined to be a character area,
Outputs “1”.

In other words, the character area is extracted by utilizing the property that the connected high-level pixels and the connected low-level pixels are simultaneously present at a certain density or higher in the outline portion of the character.

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

The color determination circuit 12 is a circuit that determines the color of the pixel of interest or the block of interest, binarizes the C2, M2, and Y2 data of the pixel of interest with a predetermined threshold.
> Threshold m, Y2> threshold y, black, C2 ≤ threshold c, M2
> Threshold m, Y2> red if threshold y, C2> threshold c, M2
If ≤ threshold m and Y2 ≤ threshold y, it is determined that the color is cyan. In this case, there are eight types of colors. In the case of the target block, an average is obtained for each of C, M, and Y in the block, and then binarized with a predetermined threshold to determine the color.

The primary determination circuit 13 determines a character area and a picture area based on outputs from the color determination circuit 12 and the character detection circuit 11, and determines the character color of the character area.

The determination correction circuit 14 is a circuit provided according to the present invention, and when the pixel of interest belonging to the minute picture area determined by the primary determination circuit 13 is surrounded by a black character area,
The target pixel is re-determined as a black character area. Judgment correction circuit
In FIG. 14, a correction pattern as shown in FIG. 6 or FIG. 7 is prepared, and when matching with this pattern, the pixel of interest is determined to be a black character area.

The pattern shown in FIG. 6 is a pattern in which the target pixel P is a picture region, the pixels a1 to a5 surrounding the target pixel P are black character regions, and the pixels b5 to b9 are black character regions. In the pattern of FIG. 7, the pixel of interest P is a picture region, and for example, the pixels 1a and b3 surrounding the pixel of interest P are black character regions, or the pixels of c1 and d3 are black character regions. It is a pattern.

Therefore, the black character area is reproduced (printed) in a single black color by the color printer 9, and in the case of the picture area, Y,
The pattern is processed by three colors of M and C or four colors of Y, M, C and Bk.

In the above-described embodiment, a small pattern area surrounded by black character areas is targeted for correction. However, the present invention is not limited to this, and a small pattern area surrounded by specific color characters is targeted for correction. It can also be.

[Effects of the Invention] As described above, according to the present invention, since the small pattern area surrounded by the black character area is determined as the black character area, not only the edge of the black character, but also the inside of the black character area is black. Therefore, the reproduced image quality can be greatly improved, and the amount of ink consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2 (a) to 2 (f) are diagrams for explaining UCR processing, and FIG. 3 is an example of a character detection circuit. A block diagram showing the
4 and 5 are diagrams showing a pattern for character detection, FIGS. 6 and 7 are diagrams showing a pattern for correction, and FIG. 8 is a diagram showing a result of a conventional black character determination. It is. 1 ... input sensor, 2 ... A / D converter, 3 ... log conversion circuit, 4 ... masking circuit, 5, 6 ... UCR circuit, 7 ... binarization circuit, 8 ... dither circuit, 9 ... Selection circuit, 10 ... Color printer, 11 ... Character detection circuit, 12 ... Color judgment circuit, 13 ... Primary judgment circuit, 14 ... Judgment correction circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 1/60 B41J 3/00 B

Claims (1)

(57) [Claims] 1. A color image processing apparatus for digitally reading a color original and reproducing a color image by multi-color superimposition using yellow, magenta, cyan, and black color materials based on the read color image data. A character detecting means for detecting whether or not a target pixel of the color image data is a character area; a color determining means for determining a color of the target pixel; a detection result of the character detecting means; Determining means for determining the pixel of interest into a black character area and a picture area based on the determination result of the means;
Means for changing the determination of the first pixel of interest to a black character area when the target pixel is surrounded by a black character area, and means for reproducing the determined black character area in a single black color. Color image processing device.