JPH04115669A - Color picture processor - Google Patents

Abstract

PURPOSE:To improve reproduced picture quality by discriminating a small picture pattern area enclosed by a black character area as the black character area and reproducing the edge and the inner part of a black character in black monochrome. CONSTITUTION:A character area and a picture pattern area are discriminated by output from a color discriminating circuit 12 and a character detecting circuit 11. When a specific picture element which belongs to the small picture pattern area is enclosed by a black character area, since a discrimination correcting circuit 14 discriminates that picture element as the black character area, the black character area is printed in black monochrome by a color printer 10. Accordingly, not only the edge of a black character but also the inner part of it are reproduced in black monochrome. Thus, reproduced picture quality is improved and also the consumption of ink can be reduced simultaneously.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a color image processing device that digitally reproduces a color image from a color original, and particularly to a color image processing device that performs monochromatic black processing on the inside of black characters. Regarding.

[Prior Art] For example, in the case of a color copier, it is preferable to reproduce black characters in a document in a single black color in order to improve the reproduced image quality and reduce ink consumption.

For this reason, 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 greater than or equal to a predetermined threshold value. The image may be reproduced by monochromatic black processing without applying Y, M, or C ink to the image area.

However, in the case of originals that contain both pictures (halftone images, photographic images) and text, not only the black text but also the picture parts are frequently treated with black monochrome, making it difficult to obtain desirable halftone expressions and playback. Image quality deteriorates.

For the pattern, appropriate undercolor removal processing, so-called UCR (
Under Co1 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 document in monochromatic black, there is a color image forming apparatus described in Japanese Patent Laid-Open No. 63-240175. This device includes a means for extracting a character area using the continuity of pixels at the edge of a character, and a means for detecting black from the minimum signal MIN (Y, M, C) among the Y, M, and C signals after color correction. The black character area is separated by the logical product of the detection results of each means and subjected to monochromatic black processing.

Furthermore, the applicant detects black characters in a color image,
A color image processing device for reproducing the black characters in monochromatic black has already been proposed (for example, Japanese Patent Application No. 2-118358).

[Problem to be Solved by the Invention J] However, in the above-mentioned technique, as shown in FIG.
Since the inside of the black text is processed with a pattern and reproduced with ink of four colors Y, M, C, and Bk, there is a drawback that the amount of ink consumed increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color image processing device that performs monochromatic black processing even on the inside of black characters.

[Means for Solving the Problems] In order to achieve the above object, the present invention digitally reads a color original and digitally prints the read color image data using yellow, magenta, cyan, and black inks. A color image processing device for reproducing a color image, comprising means for separating the color original data into a character area and a picture area, a means for determining the color of a local area in the color original data, and a means for separating the color original data. A means for primarily determining the color document data into a black character area and a picture area according to the output of the color determining means, and a means for detecting a minute picture area surrounded by the black text area from the picture area, and detecting the minute picture area surrounded by the black text area from the picture area; and means for changing processing by treating the area as a black text area, so that the black text area is reproduced in a single black color.

1 Action] Determine the character area and picture area based on the output from the color determination circuit and character detection circuit. The judgment correction circuit detects that when a pixel of interest belonging to a small picture area is surrounded by a black character area,
Since the pixel of interest is determined to be a black text area, the black text area is printed in a single color of black by a color printer. As a result, not only the edges of black characters but also their interiors are reproduced in monochromatic black, thereby improving the reproduced image quality and at the same time making it possible to reduce ink consumption.

〔Example〕

Hereinafter, one embodiment of the present invention will be specifically described using the drawings.

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

The input sensor 1 has a photoelectric conversion element such as a CCD camera, and reads a color document and outputs R (red), G (green), and B (blue).
It outputs color separation signals of three colors. The A/D converter 2 converts the R, G, and B signals into, for example, 8-bit digital signals. The log converter 3 converts the density of the R%G, B digital signals and generates signals CI, Ml, Yl representing the amount of each color ink of C (cyan), M (magenta), and Y (yellow).
Output. The masking circuit 4 performs color correction (masking) on the C1, M1, and Y1 signals in order to remove the turbidity component of the color separation filter of the input sensor 1 and the turbidity component of the ink, and outputs the C2, M2, and Y2 signals. This color correction is performed, for example, by the following equation.

Y2=K], 1XYI+ to 12XMl+K13XCIM
2= to 21XY1+ to 22XM1+ to 23XCIC2=
to 31XY1+ to 32XMl+ to 33XC1 (Kll~
33 is a constant determined by experiment) The UCR circuit 5.6 is a circuit that performs undercolor removal processing (UCR processing), and performs part or C3 and M3 with all removed
, Y3 signal, and a signal of 3 for the amount of black ink equivalent to removal.

In the case of a black character, the UCR circuit 5 for the character area generates a black ink signal of 3a=MIN (C2, M2.Y2). In the example of LTCR 100% in black text, Figure 2 (a)
If the Y2, M2, and C2 signals with the values shown in are input, MI
N (C2, M2.Y2) 100% of the signal is C2,
M2. The values subtracted from the Y2 signal are C3a, M3a, Y3a
So, K3a is the value of MIN (C2, M2.Y2),
In other words, it becomes Y2 (FIG. 2(b)). Similarly, in the example of UCR 100% for cyan characters, if Y2, M2, C2 signals with values shown in FIG. 2(c) are input, 3a will be input to C3a, M3 a, with values shown in FIG. A signal is generated.

The UCR circuit 6 for the picture area has MIN (C2°M2.
The values obtained by subtracting, for example, 50% of the Y2) signal from the C2, M2, and Y2 signals become C3b, M3b, and Y3b, and K3b
is a so-called 50% UCR process that generates a signal with a value of MIN (C2, M2.Y2), as shown in Figure 2 (e).
In the case of the input data shown in FIG. 2(f), a 3b signal is generated at C3b, M3b, and Y3b with values shown in FIG. 2(f).

The binarization circuit 7 is a circuit that binarizes the C3a, M3a, and Y3a signals using predetermined threshold values, and outputs the signals C4a and C4a.

Y4a and Y4a are respectively input to the selection circuit 9.

The dither circuit 8 is a circuit that binarizes the 3b signals C3b, M3b, Y3b, by a systematic dither method, and the output signals C4b, M4b, Y4b, 4b are input to the selection circuit 9.

The selection circuit 9 selects signals C4b and M4b output from the dither circuit 8 for pixel areas that are determined to belong to the picture area based on a control signal from the determination correction circuit 14, which will be described later.
, Y4b, and for a pixel area determined to belong to a black character area, 4a is selected as the signal output by the binarization circuit 7, and the pixel area is determined to be a pixel belonging to a color character area, for example, a cyan character. The signal C4a output from the binarization circuit 7 is selected for the pixel area that has been selected.

In the color printer 10, a color image is reproduced by receiving a signal from the selection circuit 9 and turning on/off ink dots of each color.

The character detection circuit 11 is a circuit that extracts a character area on a color document.
+βG+γB signal, or max (R, G, B) signal), or 7% M, C signal representing the amount of ink (αY+βM+γC signal, which is a linear combination of them, or max
(Y, M.

C) Signal). Here, α, β, and γ are coefficients, which are determined through experiments or the like.

In this example, αY2+βM2+ after masking processing
A pixel area where a part of a character and a part of a white background continuous to the character coexist is detected from the γC2 signal.

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 in Japanese Patent Application No. 2-118358).
. Character detection is performed as follows. That is, the binarization circuit 31 binarizes the MIN (C2, M2.Y2) signal into low level/non-low level according to a predetermined threshold value, and then inputs the signal 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 pixel of interest as the center pixel is matched with any of the patterns shown in FIG. The counting circuit 33 calculates the number of "1" outputs from the low-level pixel pattern matching circuit 32, that is, the number of character low-level pixels, for example, in a 3x3 grid centered on the pixel of interest. The matrix is counted, and when the counted value is equal to or greater than a certain value (for example, 2), "1" is output.

Further, the binarization circuit 34 binarizes the MAX (C2, M2° Y2) signal, which is the maximum signal among the C2, M2° Y2 signals, into high level/non-high level according to a predetermined threshold value, and then converts it 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 pixel of interest as the center pixel is matched with any of the patterns shown in FIG. It is determined that
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 from the output of the high level pixel pattern matching circuit 35, and when the count value is a constant value (for example, 2
), outputs 1'''.

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 exist simultaneously 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 set as a temporary character pixel.

For example, if there are a certain number or more of the temporary character pixels in a 5 x 5 matrix centered around the pixel of interest, the determination circuit 38 determines the pixel of interest or a block of a certain size (5 x 5 matrix) containing the pixel of interest. is determined to be a character area, and '1
” is output.

That is, a character area is extracted by utilizing the property that connected high-level pixels and connected low-level pixels exist simultaneously at a certain density or more in the outline of a character.

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

The color determination circuit 12 is a circuit that determines the color of a pixel of interest or a block of interest, and is a circuit that determines the color of a pixel of interest or a block of interest. Y2 data is binarized using a predetermined threshold, for example, if C2>threshold C, M2>threshold m, and Y2>threshold y, then black, C
If 2≦threshold C, M2) threshold m, and Y2) threshold y, the color is determined to be red, and if C2>threshold C, M2≦threshold m, and Y2≦threshold y, the color is determined to be cyan. In this case, there are eight types of colors. In addition, in the case of the block of interest, C in the block,
The average is taken for each of M and Y, and then binarized using a predetermined threshold value to determine the color.

The primary judgment circuit 13 includes a color judgment circuit 12 and a character detection circuit 1.
A character area and a picture area are determined based on the output from 1, and the character color of the character area is determined.

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 -next determination circuit 13 is surrounded by a black character area, the determination correction circuit 14 determines that the pixel of interest belongs to the black character area. Re-judge. The determination correction circuit 14 is prepared with a correction pattern as shown in FIG. 6 or 7, and determines that the pixel of interest is a black character area when it matches this pattern.

In the pattern of FIG. 6, the pixel P of interest is a picture area,
For example, the pattern surrounding the pixel of interest P is that the pixels al to C5 are black text areas, and the pixels b5 to b9 are black text areas, and the pattern in FIG.
The pixel of interest P is a picture area, and the pixels surrounding the pixel of interest P, for example, al and b3, are black text areas, or C1 and d.
This is a pattern in which pixels No. 3 are composed of black character areas.

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

The pattern is processed using the four colors of Bk.

Note that in the above embodiment, the correction target is a small picture area surrounded by black text areas, but the present invention is not limited to this, and the correction target is a small picture area surrounded by specific color text. It is also possible to do this.

[Effects of the Invention] As described above, according to the present invention, a small picture area surrounded by a black character area is determined as a black character area, so that not only the edges of the black character but also the inside thereof are solid black. Therefore, the reproduced image quality can be greatly improved and the amount of ink consumed can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2(a) to 2(f) are diagrams for explaining OCR processing, and FIG. 3 is an example of a character detection circuit. A block diagram showing
Figures 4 and 5 are diagrams showing patterns for character detection, Figures 6 and 7 are diagrams showing patterns for correction, and Figure 8 is a diagram showing patterns for character detection.
The figure shows the results of conventional black character determination. 1... Input sensor, 2... A/D converter, lo
g conversion circuit, 4 6... UCR circuit,... dither circuit, 9... O... color printer, 2... color judgment circuit, 1 4... judgment correction circuit.・Masking circuit, 7...Binarization circuit, selection circuit. 11...Character detection circuit, 3...-order judgment circuit, Fig. 2 (0-) UCG simple Fig. 2 (C) L/CB sieve Fig. 2 (Rishi) CFl! Zuyu (J! Yugoshitsu System p Figure 2 (cl)
) LICP! Figure 2 (e) Figure 2 is similar to Figure 3. ! I rate

Claims (1)

[Claims] (1) Digitally read a color original and use the read color image data as yellow, magenta, cyan,
In a color image processing device that digitally reproduces a color image using black ink, means for separating the color original data into a character area and a picture area, and determining the color of a local area in the color original data. means for primarily determining the color document data into a black character area and a picture area according to the outputs of the separating means and the color determining means; and a minute picture area surrounded by the black character area from the picture area. 1. A color image processing apparatus, comprising: means for detecting a small picture area and changing processing by treating the minute picture area as a black character area, and reproducing the black character area in a single black color.