JPH0646251A - Color picture processing unit and conversion method - Google Patents

Abstract

PURPOSE:To provide the color picture processing unit and its conversion method warranting the reproduction of an achromatic color and mapping a 1st color reproduction range onto a 2nd color reproduction range. CONSTITUTION:A minimum value extraction circuit 101 extracts the minimum value in R, G, B color picture signals and subtractor circuits 102-104 obtain each difference signal. Then a matrix conversion circuit 111 applies matrix conversion to outputs from latches 105-107 latching difference signals and from multiplier circuits 108-110 calculating the secondary term of the difference signals and succeeding adders 112 114 add the result to the original R, G, B signals and a desired color separation signal is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention particularly relates to a color image processing apparatus and a conversion method for converting a first color separation signal into a second color separation signal in a color image processing apparatus.

[0002]

2. Description of the Related Art At present, a color CRT monitor device or a color hard copy device is known as a general device for visualizing and outputting a color image. The former intensity-modulates the emission levels of R, G, and B color phosphors on the tube surface and forms a visible image by additive color mixing. On the other hand, the latter is Y (yellow), M (magenta), C (cyan), and K.
A color image is formed on the paper by subtractive color mixing using a (black) color material.

[0003]

However, in the above-mentioned conventional example, the above-mentioned image display device is basically different in color reproducibility, and as shown in FIG. Wide reproduction range. Therefore, when there are two colors of point A and point B in a certain image, this image is reproduced as a different color when displayed on a CRT, but in hard copy, both points A and B are reproduced as point C. As a result, the two colors cannot be distinguished from each other, and as a result, the information originally contained in the image is lost.

Therefore, in the case of outputting an input color image by hard copy, a method of converting the color signal in the image so that it falls within the color reproduction range of the hard copy and then outputting it is conceivable. That is, point A shown in FIG. 2 becomes point D,
If the conversion is performed so that the point B becomes the point E, the colors can be distinguished even on the hard copy. However, there is not one such conversion method, and depending on the method, the output image may be totally unnatural.

In order to solve such a problem, the CRT color reproduction range is mapped to the hard copy color reproduction range while the basic primary colors (red, green, blue, cyan, magenta, yellow) of the color image are stored. It is possible. However, in this case, there is a problem that reproduction of an achromatic color (gray) is not guaranteed (the achromatic color on the CRT does not become an achromatic color on the hard copy).

The present invention has been made to solve the above-mentioned problems, and guarantees the reproduction of an achromatic color and maps a first color reproduction range to a second color reproduction range, and The purpose is to provide a conversion method.

[0007]

In order to achieve the above object, the structure of the present invention has a first color separation in a color image processing apparatus for converting a first color separation signal into a second color separation signal. Extraction means for extracting the minimum value from the signal for each pixel, generation means for generating a difference signal between the minimum value extracted by the extraction means and the first color separation signal, and the generation means. And a conversion means for converting the first color separation signal into the second color separation signal based on the difference signal.

[0008]

With the above arrangement, the minimum value of each pixel is extracted from the first color separation signal, and the difference signal between the extracted minimum value and the first color separation signal is generated. Then, it operates so as to convert the first color separation signal into the second color separation signal based on the generated difference signal.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the drawings. [First Embodiment] FIG. 1 is a block diagram showing a circuit configuration for realizing color signal conversion in the first embodiment. In the figure, an input color image signal is input from the upper side of the drawing, and the image signal is sequentially transferred to the lower side of the drawing together with a drive clock, a reset signal and the like not shown.

Reference numeral 101 denotes a minimum value extraction circuit for extracting the minimum value of R, G and B, and a minimum value signal X (= min
(R, G, B)) is output. 102, 103, 104
Is a subtraction circuit for obtaining the difference between the input signal and the extracted minimum value signal, 102 is R-X, 103 is G-X, 104
Outputs BX respectively. 105, 106, 107
Is a latch circuit for temporarily latching the outputs of the subtraction circuits 102, 103, 104. 108, 109, 110
Is a multiplication circuit for calculating the above-mentioned two items R-X, G-X, and B-X, and 108 is (R-X) * (G-X), 10
9 is (G−X) × (B−X), 110 is (B−X) ×
(R-X) is output.

Reference numeral 111 denotes a matrix conversion circuit for matrix-converting the six outputs obtained by the above-mentioned arithmetic circuit. Specifically, the following arithmetic operations are performed to calculate dR, dG,
Output dB respectively.

[0012]

[Equation 1]

Matrix conversion coefficient a used here
_ij is obtained by the method described later. 112, 113, 11
Reference numeral 4 denotes an adder for adding the original R, G, B signals to the dR, dG, dB obtained by the above formula (1), and outputs converted color separation signals R ', G', B '. To do. That is,
The following equation (2) is executed.

[0014]

[Equation 2]

Next, a method of _obtaining the matrix conversion coefficient a _{ij in} the above equation (1) will be described. The purpose of the matrix conversion is to map colors in a wide color reproduction range such as CRT to the color reproduction range of hard copy, but in the following, red reproduction will be considered first. If the image signal is represented by 8 bits for each of R, G, and B,
The most saturated red that can be reproduced on a CRT is R = 25
The color signals are 5, G = 0, and B = 0. This color is shown in Figure 2.
It is at the R _c point on the chromaticity diagram. However, since the most saturated red color that can be reproduced by hard copy is the _RH point, all the colors between the _RH point and the R _C point are output in hard copy as the color of the _RH point in the normal method. Will end up.

On the contrary, when the color signal value at the R _H point is expressed by R, G, B signals, it is usually about R = 160, G = 20, B = 10. Therefore, the input color signal R = 25
5, G = 0, B = 0 are converted by the matrix conversion circuit so that R ′ = 160, G ′ = 20, B ′ = 10, the R _c point is converted to the R _H point, and the color between them is _RH
The color reproduction area of the CRT can be mapped to the color reproduction area of the hard copy while the primary colors of the input signal are preserved while being mapped inside the points.

If such correspondences are set for all six primary colors, then 18 simultaneous linear equations can be formed from the above equations (1) and (2). Since there are still 18 a _ij as unknowns, they can be uniquely solved and the matrix conversion coefficient can be determined. An example of the above correspondence is shown below. Red: R = 255, G = 0, B = 0 ⇒ R '= 160, G' = 20, B '= 10 Green: R = 0, G = 255, B = 0 ⇒ R' = 20, G '= 100, B '= 20 Blue: R = 0, G = 0, B = 255 ⇒ R' = 15, G '= 10, B' = 100 Cyan: R = 0, G = 255, B = 255 ⇒ R ' = 10, G '= 95, B' = 200 Magenta: R = 255, G = 0, B = 255 ⇒ R '= 200, G' = 10, B '= 90 Yellow: R = 255, G = 255, B = 0.fwdarw.R '= 255, G' = 250, B '= 10 (3) By the above procedure, the desired color signal conversion of the formula (1) can be obtained. At this time, considering the case where an achromatic color signal is given as an input signal, since the achromatic color is R = G = B, the minimum value signals X are also equal. That is, the output of each of the subtraction circuits 102, 103, 104 becomes "0", and the matrix conversion result also becomes dR, dG, dB = 0. Furthermore, the output signals R ', G', B'are unaffected by the conversion,
The value of the input signal is obtained as it is, and the achromatic signal is preserved.

[Second Embodiment] In the first embodiment, CR is used.
All colors that can be reproduced by T are mapped within the color reproduction range of the hard copy, but the input image does not always include all the colors within the reproduction range of the CRT. Therefore, as a second embodiment, a case of adaptively changing the matrix conversion coefficient of the equation (1) will be described. FIG. 4A is a diagram schematically plotting the color reproduction range of the CRT and the color reproduction range of the hard copy on the RGB signal space. As shown in the drawing, a cube 401 represents a CRT color reproduction range, and a deformed cube 402 represents a hard copy color reproduction range. Here, the color signal included in the input image is first sampled to RG.
The color with the highest saturation is detected in the B color space, and the matrix coefficient of the equation (1) is determined from the detected color. Now, let the signal value of a pixel in the input image be R _S ,
G _s and B _s, and their positions are S points 4 in (a) shown in FIG.
03.

Here, it is necessary to obtain the RGB signal values of the most saturated colors of the R, G, B, Y, M, and C6 primary colors among the signal values included in the input image. Therefore, consider a vector as shown in FIG. In this example, the case of the M (magenta) direction is shown. M _H is the coordinates of the hard copy magenta in the RGB space, M _C is the coordinates of the CRT in the RGB space, and is shown in FIG.
Is the same as

First, the vector M _H from M _H to the input color S
Take S, and the vector M _H M _C from M _H to M _C , M
The direction cosine r _M of _H S in the M _H M _C direction is determined. It can be seen that the larger r _M is, the higher the saturation of the input color S in the magenta direction is. This r _M can be obtained by the inner product calculation of the equation (4) shown below. r _M = (M _H S, M _H M _C ) / | M _H M _C | (4) Here, (X, Y) is the inner product of the vectors X and Y, and | Z | is the absolute value of the vector Z. is there.

Similarly, for the other primary colors, the direction cosines r _R , r _G , r _B , r _Y , and r _C of that direction are obtained, and if the maximum one is selected from these, which direction (hue) )
You can see if it is the color of. In this way, if the maximum value of the direction cosine is obtained for each primary color for all pixels in the input image, or for pixels sampled at regular intervals, the RGB signal value when the maximum value is given is the color signal to be obtained. It becomes a value.

FIG. 5 is a flow chart showing the above-mentioned processing procedure. First, in step S1, the maximum values R _max , G _max , B _max , Y _max , and M of the direction cosine in the primary color direction are obtained.
Initialize _max and C _max , respectively. In step S2, the R, G, and B values of the specific pixel are read from the input image, and in step S3, the direction cosines r _R and r of the six primary color directions are read.
_{Determine G} , r _B , r _Y , r _M , r _C. Then, in step S4, the maximum value of each direction cosine is obtained, and in step S5 the maximum value is set as r _X (hereinafter, X is R, G,
Either B, Y, M, or C).

Next, in step S6, the maximum value r _X
Is larger than X _max , X _max is replaced with r _X , and the R, G, B signal values at this time are stored as the maximum saturation color signal in the X direction in step S7. Then, step S8
In step S2, it is checked whether or not all the pixels to be sampled have been processed.
The process is returned to and the above process is repeated. After that, when all are finished, the process proceeds to step S9, and the matrix conversion coefficient is obtained from the maximum saturation color signal.

The RGB signal values thus obtained are replaced with the data on the left side of the correspondence relationship between the primary colors shown in the equation (3). Then, if the matrix conversion coefficient is obtained from the replaced correspondence in the same manner as described above, it becomes the optimum conversion coefficient for the input image. As described above, according to the embodiment, a CRT having a wide color reproduction range is provided.
It is possible to convert a color image displayed on a monitor or the like into a color image signal suitable for hard copy output without losing the original amount of information. Further, at this time, the gray balance of the original image is not impaired.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0026]

As described above, according to the present invention,
It is possible to guarantee the reproduction of an achromatic color and to map the first color reproduction range to the second color reproduction range.

[Brief description of drawings]

FIG. 1 is a circuit block diagram for realizing color signal conversion in a first embodiment.

FIG. 2 is a diagram illustrating a difference in color reproduction range between a CRT and a hard copy.

FIG. 3 is a diagram illustrating a state of color signal conversion according to the first embodiment.

FIG. 4 is a diagram illustrating a method of detecting a maximum saturation color in an input image.

FIG. 5 is a flowchart of a method for detecting a maximum saturation color in an input image.

Front page continuation (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G06F 15/68 310 9191-5L H04N 1/46 9068-5C

Claims (6)

[Claims] 1. A color image processing apparatus for converting a first color-separated signal into a second color-separated signal, and an extracting means for extracting the minimum value of each pixel from the first color-separated signal, and the extracting means. Generating means for generating a difference signal between the minimum value extracted in step 1 and the first color separation signal, and the first color separation signal based on the difference signal generated by the generating means. A color image processing device, comprising: a conversion unit that converts the signal into a signal. 2. The first and second color separation signals are R,
The color image processing apparatus according to claim 1, wherein the color image signal is represented by G and B. 3. The conversion means includes means for matrix-converting the difference signal, and adaptively sets conversion coefficients in the matrix conversion according to a color signal distribution of an input image. Color image processing device. 4. The conversion coefficient includes means for performing an inner product operation of a vector determined by a predetermined color signal value and a vector determined by an input color image signal value, and means for detecting a maximum value of the inner product values. 4. The color image processing according to claim 3, wherein the color image processing is determined by means for storing an input color signal value when the maximum value is obtained and means for obtaining a solution of a simultaneous equation determined by the color signal value. apparatus. 5. The color image processing apparatus according to claim 4, wherein the predetermined color signal value is a value that reflects a color reproduction range of an output device that visualizes and outputs a color image signal. . 6. A conversion method for converting a first color separation signal into a second color separation signal, an extraction step of extracting a minimum value of each pixel from the first color separation signal, and an extraction step in the extraction step. Generating a difference signal between the generated minimum value and the first color separation signal, and converting the first color separation signal into a second color separation signal based on the difference signal generated in the generation step. And a converting step of converting.