JPS61208974A - Color image processing method - Google Patents

Abstract

PURPOSE:To obtain a fine color tone and to express more natural color tints by making each of the plural picture elements of one image a combination of threshold matrices of each plural colors, and by selecting the said threshold matrices to obtain the color tone of the picture elements. CONSTITUTION:The control program of a CPU 2 is stored in a ROM 4 connected to the data bus line 3 of a color printer device 1, the data constituting the threshold matrices are stored in a ROM 5, and the parameters of the threshold and others are stored in a RAM 6. Also, an image data is stored in a image memory 7 to which an image inputting means 8 of a TV camera etc. is connected with the memory 7. The screen 10 of the equipment is constituted by pictures 10R, 10G, and 10B made respectively by R, G, and B-signals. And the screen 10 are also made up of specified number of picture elements P1, P2, P3,.... Respective threshold matrix is set for each one of the picture elements P1, P2, P3,..., and image data 12 decided by the matrix is supplied to a colot printer 9 to provide a printing of fine color tone.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color image processing method that converts a color halftone image read pixel by pixel into a color pseudo density pattern using a threshold matrix.

BACKGROUND ART In order to binarize the luminance level of a grayscale image as a pseudo-density pattern, an area modulation method such as a dither method or a density pattern method has conventionally been used. When expressing color gradation images using this area gradation method, a method known as color gradation has been used. Among these processes, tone correction is a process performed for the purpose of correcting gradation characteristics. Conventionally, tone correction has been performed by adjusting the contents of a matrix that stores binarization thresholds, usually called a threshold matrix. This method will be explained using FIG. 5.

The data of each original image is stored in the matrix 41 as a density value. The data in this matrix 41 is compared for each component of the threshold matrix 42, and the data is
It is valued.

This binarized information is then stored in the matrix 43 as image data. If the threshold value of the threshold value matrix 42 is changed here, the number of points to be colored in the matrix 43 changes for the same original image.

That is, it becomes possible to change the gradation characteristics of the output. The tone correction conventionally performed in this way is
Correction was performed by changing the number of points colored by value conversion.

Problems to be Solved by the Invention In the above-mentioned prior art, the range of correction is limited because gradation correction is performed by changing the number of dots.

Therefore, it is not suitable, for example, when more delicate gradation correction is required depending on the characteristics of the ink.

An object of the present invention is to provide a color image processing method that can solve the above-mentioned technical problems, can obtain fine gradation characteristics, and can express natural color shading.

Means for Solving the Problems In the present invention, one image consists of a plurality of pixels, each pixel consists of a combination of threshold matrices for each of a plurality of colors, and each threshold matrix is selected to obtain the tone of the pixel. This is a color image processing method characterized by the following.

According to the present invention, threshold matrices for each of a plurality of colors are prepared,
By selecting each threshold value matrix to obtain an arbitrary combination, it is possible to control how multiple colors are mixed. This makes it possible to obtain fine color tones.

Embodiment FIG. 1 is a system diagram for explaining a color image processing method according to the present invention, and FIG. 2 is a block diagram of a color printer device 1 in which the present invention is used. First, referring to FIG. 2, the processing circuit 2 includes a read-only memory (ROM) 4 that stores a control program for the processing circuit 2 via a data bus line 3, and a threshold value matrix that will be described later. ROM5 that stores data and random access memory (RAM5) that stores threshold variables, etc.
) 6 and an image memory 7 for storing image data. An image input means 8 such as a TV camera is connected to the image memory 7. Further, a color printer 9 is connected to the data bus line 3.

Referring to FIG. 1, the screen 10 basically has a red color signal (
Each of the images 10R, IOG, and 10B is constituted by signals composed of a green color signal (R signal), a green color signal (G signal), and a blue color signal (B signal). Here, the screen 10 has, for example, 256×256 pixels P1, P2, P3,
Consists of... Each pixel P is given multivalued image data, which is the level of an R signal in hexadecimal numbers, for example. Each of these pixels P1°P2. For example, a threshold matrix 11 of 8 rows and 8 columns is set for P3, . . . , respectively. Each element of this threshold matrix 11 is given threshold data, for example, in hexadecimal. This threshold matrix 11 corresponds to the three primary colors of ink: yellow threshold matrix 11Y1, magenta threshold matrix 1
1M1 and a cyan color threshold matrix IIC are prepared in advance (collectively referred to as 11). In each threshold matrix 11, each screen 10 of the image 10
Level discrimination is performed regarding the level of each color signal of each pixel for each color signal of R, 10G, and 10B, and a binarized image data 12 is obtained through this level discrimination. For example, in the case of the image 10R, this image data 12 includes each pixel P1.
, P 2 , P 3 . . . , and the same process is performed for each pixel of images 10G and IOB.
+fl color printer 9.

Note that, prior to the above-described processing regarding the images 10R, IOG, and IOB, the above-described processing is performed on pixels that display white on the screen 10, that is, pixels that share the R signal, G signal, and P signal. . If all of the image data 12Y1 obtained by the yellow threshold matrix 11Y, the image data 12C1 obtained by the cyan threshold matrix 11C, and the image data 12M obtained by the magenta threshold matrix 11M are logical "1", a dot is For the image data related to the black color signal, the black printer head H
13>1wA is operated.

The color printer 9 includes the black printer head H.
A cyan printer head HC, a magenta printer head IM, and a yellow printer head HY are provided. In response to the output from the image data 12, each printer head HB, HC, HM, HY is driven to eject ink of each color to perform desired color printing.

FIG. 3 is a diagram for explaining the principle of tone correction of the present invention. As shown in Figure 13 (1), 3x
Yellow (Y), magenta (M), cyan (
C) are marked with three points each.

On top of this, add magenta by 1 in the state shown in Figure (1).
Assume that the points are increased. In such a case, the third
There are two possible cases: magenta overlaps with yellow and becomes red, as shown in Figure (2), and magenta overlaps with cyan and becomes blue (B), as shown in Figure 3 (3). . The conventional method of controlling only the number of dots does not take these two differences into account.

According to the experimental results of the present inventor, it was found that the $3 figure (2) has a reddish hue than the figure 3 (3). Based on this principle, it is possible to correct the gradation characteristics by controlling the method of applying mixed colors.

The method of applying this color mixture is controlled by independently setting threshold matrices for each color. For example, in order to obtain a tone with less redness, the threshold matrix 11 may be set in advance so that red points, that is, points where two colors, yellow and magenta, are mixed are unlikely to occur. Furthermore, if it is desired to suppress blueness due to the characteristics of the ink, the threshold value matrix 11 may be set in advance so that blue points, that is, points where two colors of magenta and cyan are mixed, are less likely to occur.

The operating state of the present invention will be explained with reference to FIG. Fourth
1) to 4(3) show specific examples of threshold matrices in the case where red is suppressed.

FIG. 4(1) shows a yellow threshold matrix IIY,
FIG. 4(2) shows a cyan threshold matrix 11C, and FIG. 4(3) shows a magenta threshold matrix I.
IM is shown. Further, FIG. 4 (4) shows a recording paper A on which color printing is performed based on image data binarized by the threshold matrices 11Y, 11C, and 11M. The threshold matrices 11Y, 11C, 11M are
For example, there are 7 matrices arranged in 4 rows and 4 columns, and numbers 1 to 16 shown in components a and ~a41 of each matrix are printed on recording paper A in the order of the numbers when the input density value becomes high. A dot corresponding to the number is added (indicates that).
When the colors are mixed, red is obtained, when yellow and cyan are mixed, green is obtained, and when cyan and magenta are mixed, blue is obtained.

Further, when the three colors yellow, cyan, and magenta are mixed, black is obtained. Furthermore, of course, the parts that have not been inked will be white. Note that each threshold matrix Xi
Portions of the recording paper A corresponding to the components IY, 11C, and ILM all to a44 are indicated with AI1 to A44.

First, when the input density value is the first level of MtJ, each component lz of each threshold matrix 11Y, 11C, 11M
The part A11 of the record MkA corresponding to # is yellow, cyan,
Each magenta dot is added in an overlapping manner. As a result, as shown in the first row of Table 1 (,), the partial Al
Black (BL) dot only on l - #1 Tsuhi 1i -
-ni-1, khz tA7t-1ftRAS-AjQ-
AAJ-146 colors (W>, so there are 15 white dots.

(Margins below) In the same manner as in Table 1 and below, when the input density values to the threshold matrices IIY, IIM, and 11C become 2 to 4 as shown in columns 2 to 4 of Table 1 (a), The black dot is 1
The number of dots continues to increase, and the white dots decrease by one.

Next, when the input density value is 5, a yellow dot is generated in the portion A21 of the recording paper A corresponding to the component &2+ of the yellow threshold matrix 11Y, as shown in FIG. 4(1). Further, as shown in FIG. 4(2), a cyan dot is generated in a portion A22 of the recording paper A corresponding to f122 of the threshold value matrix IIC. Furthermore, as shown in FIG. 4(3), magenta dots are generated in the portion A12 of the recording paper A corresponding to the component a+2 of the threshold value matrix 11M. Therefore, yellow dots are generated in portion A21 of recording paper A, cyan dots are generated in portion A22, and magenta dots are generated in portion A12. As a result, as shown in the fifth row of Table 1 (a), yellow,
One dot of each color, magenta and cyan, is generated.

This reduces the number of white dots by three. Below, when the input density value reaches the 6th level to the 8th level, Hiiragi will display a yellow color as shown in the 6th line to fi8th line of Table 1 (a) in the same way as in the case of the 5th level described above. , magenta, and cyan dots increase by one, and white dots decrease by three.

Next, when the input density value reaches the ninth level, the threshold value matrix 11Y is set as shown in FIG. 4(1).
A yellow dot is added to the portion A22 of the recording paper A corresponding to the component a22 of the component a of the threshold matrix 11C shown in FIG.

A cyan dot is added to the portion A12 of the recording paper A corresponding to 2, and a cyan dot is added to the portion A2 of the recording paper A corresponding to the component a22 of the threshold value matrix 11M shown in FIG. 4(3).
A magenta dot is added to 2. As a result, in the portion A22 of the recording paper A, yellow dots, magenta dots, and cyan dots are mixed to form black. Furthermore, in the portion A12 of the recording paper A, magenta dots and cyan dots are mixed to generate blue (B) dots. As a result, as shown in row 9 of Table 1 (a), there are 4 yellow dots, 3 magenta dots, 3 cyan dots, and 1 blue dot. Therefore, there are 5 black dots and 0 white dots.

When the input density value reaches the 10th level, as in the case where the input density value is the 9th level, Table 1 (a
), there are 4 yellow dots, 2 magenta dots, 2 cyan dots,
Two blue dots and six black dots are generated.

Next, when the input density value reaches the 11th level, the threshold value matrix 11Y is applied as shown in FIG. 4 (1).
A yellow dot is added to the recording paper A13 corresponding to the component a13 of the threshold value matrix 11C, and a cyan dot is added to the portion A21 of the recording paper A corresponding to the component a21 of the threshold value matrix 11C, as shown in FIG. 4(2). Figure 4 (
A magenta dot is added to a portion A13 on the recording paper corresponding to component a+3 of the threshold matrix IIM shown in 3). As a result, in part A13 of recording paper A,
Black dots are obtained by mixing yellow dots, magenta dots, and cyan dots. Furthermore, recording paper A
In part A21, yellow dots and cyan dots are mixed to generate green (G) dots. Therefore, as shown in row 11 of Table 1 (a), there are 3 yellow dots, 2 magenta dots, 1 cyan dot, and 1 green dot. , two blue dots and seven black dots are generated.

Thereafter, when the level of the human concentration value reaches the 12th level to the 16th level, the dots of each color are changed to the 12th level in Table 1 (a) in the same manner as in the case of the 12th level described above.
The number of sheets shown in the lines 1 to 16 is applied to the recording paper A.

In this way, the threshold matrices 11Y, 11 shown in FIG.
By using C, 11M, it is possible to display black and white halftones on the recording paper A without the proportion of red (R). The reason why red dots do not appear is that before yellow and magenta are mixed,
The threshold matrix 11 is adjusted so that the cyan color is mixed.
This is because Y, 11C, 11M are configured in advance.

Table tA1 (b) above shows how many color dots are generated when the number of yellow, magenta, and cyan dots increases by one point from the state shown in Table 1 (a). As is clear from Table 1 (1)), the occurrence of red dots is suppressed, and a color tone with suppressed redness can be obtained. In this way, when mixing each color, by adjusting which color is mixed with priority, it becomes possible to easily obtain a tone with less redness or a color tone with less bluishness.

Therefore, even if the characteristics of the ink differ slightly due to differences in manufacturing conditions, for example, by following the method of the present invention, it is possible to obtain a color density image that is closer to the original image.

In the above embodiment, the threshold matrices IIY, 11C, II
Although one each of M is prepared, a plurality of each of these threshold matrices 11Y, 11C, and 11M are prepared in advance, and the gradation characteristics can be adjusted by arbitrarily selecting and combining each of the threshold matrices 11Y, 11C, and 11M. It is now possible to finely adjust the color tones, making it possible to obtain finer tones that are even more subtle than before.

Furthermore, although three colors, yellow, magenta, and cyan, are used for the threshold matrix 11, threshold matrices of a plurality of other colors may be prepared. Furthermore, although the present invention was applied to a color printer in the above-described embodiment, the present invention can be suitably implemented in a wide range of other technical fields.

Effects of the Invention As described above, according to the present invention, by selectively combining a plurality of threshold matrices, it is possible to control how each plurality of colors is superimposed, and thereby it is possible to obtain fine color tones. , it becomes possible to perform more natural ht-shade expression.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of one embodiment of the present invention, and Fig. 2 is another one! View Roro h1 礒;chi-+I#I+、、、、4translation 薯薯迩pus く壬+
stomach. 1. . 3 is a diagram illustrating the principle of the present invention. FIG. 4 is a diagram illustrating specific examples of threshold matrices 11Y, 11C, and 11M according to the present invention and corresponding areas of recording paper to be printed. FIG. 5 is a diagram for explaining the prior art method. 10.1 OR, 10G, 10B...image, 11.1
1Y, 11 C, 11M...threshold matrix, 12
...Image data, 13...Color printer, P 1
, P 2 , P3...pixel, HB, HC, HM, H
Y...Printer RAD agent Patent attorney Keibu Saikyo Figure 3 Figure 4

Claims (1)

[Claims] A color image processing method characterized in that one image consists of a plurality of pixels, each pixel consists of a combination of threshold matrices for each of a plurality of colors, and each threshold matrix is selected to obtain the color tone of the pixel.