JPH0533582B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a color signal conversion method for obtaining colors that faithfully reproduce changes in brightness when converting images from a color television or the like into hard copies.

(Technical background of the invention and its problems) Recently, there has been an increasing trend to make a hard copy of a scene from a color television or the like and preserve it for a long time to enjoy it. In this case, the color TV's blue
A hard copy is created by developing yellow (Y), magenta (M), and cyan (C) dyes in the color photosensitive material, respectively, based on the (B), green (G), and red (R) signals. .

As a concrete method, the first idea is to determine the amount of Y coloring based only on the B signal, the amount of M coloring based only on the G signal, and the amount of C coloring based only on the R signal. be. Figure 1 is a graph showing the density versus input signal level. Here, when the G and R signals are at maximum constant values, only the B signal changes from zero (point AA) to the maximum value (point BB). shows the density of yellow due to the B signal.
The density characteristic Y1 of (Y) changes from zero to the maximum value Dmax, and the density characteristic MC1 of magenta (M) and cyan (C) due to the other G and R signals always takes the maximum value Dmax and remains constant. The spectral densities at this time are as shown in Figure 2 A, B, and C. Figure A is for point AA in Figure 1, and the spectral density corresponding to point BB is Figure 2 B. It would be ideal if it looked like this, but in reality, the blue color of magenta (M) and cyan (C) colorants
Since the absorption of (B), that is, the subabsorption of the yellow (Y) component, is not zero, only the spectral density shown in Figure 2C can be obtained. In other words, it is impossible to obtain a vivid blue color that faithfully represents changes in brightness. For this vividness and brightness, CIE 1976L ^* u ^* v ^*
The vividness specified by (√( ^* ) ² + ( ^* ) ² )
Since it is commonly used to compare sensory things by plotting the brightness (L ^* ) against the brightness (L*), this will be used for explanation. Figure 3 shows the relationship between brightness and brightness, where TVO is the characteristic of color television images;
KKO indicates the characteristics of general photosensitive materials used for hard copying. If the characteristics of TVO and KKO are equal, no problems will occur when making a hard copy of a color TV image, and because they are different as shown in this figure, various ingenuity is required. be. That is, as shown in this figure, the problem arises because the color reproduction gamut of photosensitive materials is generally narrower than the color reproduction gamut of color television images. Here, Figure 4 shows the relationship between brightness and saturation in Figure 1. In the figure, the characteristic line TVO represents the characteristics of a color television image, and the hard copy characteristics in the example of Figure 1 are HC1. shown. In other words, due to the lack of brightness range,
With hard copies, it is not possible to obtain images that are colorful and have faithful changes in brightness. This tendency is remarkable in the order of blue color and green color.

The second method is to (1) use not only the B number but also other signals to determine the amount of yellow (Y), or (2) use only the G signal to determine the amount of magenta (M). (3) Use not only the R signal but also other signals to determine the amount of cyan coloring. This is a method in which, for example, the G signal of a color television is intentionally made to affect not only the magenta coloring layer of a color hard copy, but also the other two layers. For example, a black and white CRT emits light according to each of the B, G, and R signals, and the B,
Consider a system in which G and R filters are applied to create B, G, and R colored images, and a color photosensitive material or the like is exposed three times. In this method, when the B, G, and R signals change together, that is, when a gray scale is displayed on the TV, yellow (Y), magenta (M),
It is necessary to change the density of cyan (C) as shown in MCY2 in Figure 5. Now, if we consider the case where only the blue (B) changes as in the first example above, the yellow in this case has a slightly higher characteristic Y2 in Figure 5 than when all three signals change. It is reproduced as follows. Furthermore, since the magenta (M) and cyan (C) densities change accordingly even when only the B signal changes, they are reproduced as shown in MC2 in the figure. At this time, the yellow density at the maximum value of the B signal (point BB in the figure) does not become zero, but has a certain value like characteristic Y2, so this method also produces a bright and colorful color with high purity. It is impossible to obtain a blue color that faithfully represents change. If we plot this in terms of the relationship between chromaticity and brightness in Figure 4, we get a dashed-dotted line HC2, and although the brightness range is wider than the first method above, the complementary color relationship for blue is It is fatal that the yellow density does not reach zero, and no matter what conventional methods are used, it is impossible to obtain a hard copy that is both colorful and faithfully represents changes in brightness. A number of problems arose.

(Objective of the Invention) The object of the present invention is to faithfully reproduce the color impression of a color display image even if the color reproduction gamut of a photosensitive material to be hard-copied is narrower than the color reproduction gamut of a color display image such as a color television image. The object of the present invention is to provide a color signal conversion method for obtaining a hard copy.

(Summary of the Invention) The present invention relates to a color signal conversion method when converting a color display image into a color hard copy. The B, green G, and red R signals are each converted using the following formulas.

B′=X ₀ +FB×(B−X ₀ ) G′=X ₀ +FG×(G−X ₀ ) R′=X ₀ +FR×(R−X ₀ ) ( _where , Maximum signals FB, FG, FR of R: Any positive number less than or equal to 1) (Embodiment of the invention) Figure 6 is a graph showing the object of this invention. In terms of the relationship between
3 is in a parallel relationship with the above characteristic TVO, that is, has the same slope. As a specific numerical value, it has been found that a value of about 1.0 to 1.6 for the gradient of the characteristics of a hard copy compared to the gradient of the characteristics of a color television image is generally satisfactory.

Figure 7 shows how to output the amount of yellow (Y), magenta (M), and cyan (C) in order to achieve the above relationship. In this figure, only blue color is changed from zero. The figure shows the case where the color changes to the maximum value, and yellow can be changed as shown by straight line Y3, and magenta and cyan can be changed as shown in straight line MC3. In other words, yellow goes from point AA (zero) to BB.
For the signal level at point (maximum), from zero to maximum
By setting the density up to Dmax, and for magenta and cyan, the density is not kept at a constant Dmax value as the signal level changes, but rather decreases slightly to maintain vivid color and brightness. It was found that the blue color achieved by this method can be obtained.

Examples of the present invention will be described below. As shown in FIG. 8, quantized three-color television signals B, G, and R are input to the signal processing circuit 1. Here, first, the largest signal among the input signals is detected and the quantization level of this signal is set to X ₀ . Then, from the quantized B, G, R input signals, the following (1)
Signal level to color hard copy by formula
It is converted into B′, G′, and R′ and output.

B′=X ₀ +FB×(B−X ₀ ) G′=X ₀ +FG×(G−X ₀ ) R′=X ₀ +FR×(R−X ₀ )……(1) However, FB, FG, FR is a coefficient that defines the most colorful density, and can be arbitrarily set as a positive number less than or equal to 1. Thereafter, by coloring the Y, M, and C dyes based on the converted output signals B', G', and R', a hard copy satisfying the density relationship shown in FIG. 7 can be obtained.

FIG. 9 is a block diagram showing a specific circuit of the signal processing circuit 1. As shown in FIG. The quantized input image signals B, G, and R are input to subtracters 3, 4, and 5, and are also input to a maximum input discrimination circuit 2. The maximum input value X ₀ determined by the maximum input determination circuit 2 is input to subtracters 3, 4, and 5, and the signals B-X ₀ , G-X ₀ , which are subtracted from the input signals B, G, and R, respectively.
and R-X ₀ are input to concentration setters 6, 7 and 8. The coefficients FB, FG, and FR are multiplied by the density setters 6, 7, and 8, respectively, and inputted to the adders 9, 10, and 11 together with the maximum input value _X0 , where they are added together, and converted from the adders 9, 10, and 11. Output signals B′, G′,
and R' are output. As a result, the above equation (1) is satisfied, and color conversion signals B', G', and R' can be obtained.

Next, the above embodiment will be explained in more detail using numerical values. First, it is assumed that the input signals B, G, and R are quantized in 16 steps (4 bits) (maximum level "1", minimum level "16") as shown in FIG. In this case, as shown in FIG. 11, Y, M, and
Connect the C densities with a straight line with the maximum being Dmax, and create a Y, M, C density table for the quantized signal level for making a hard copy. After signal conversion, Y, M, It is sufficient to develop a hard copy using each dye C. In this table, an achromatic color is obtained when the three signal levels B, G, and R are the same, and the brightness of the achromatic color is equally divided by the brightness function.

Now, if blue, the most colorful color, is input, the B, G, and R signals are B=1 G=16 R=16 ...(2), and the quantization value X ₀ of the maximum signal is 1 It is. Here, if the values of FB, FG, and FR are all 12/15 and these values are substituted into equation (1), the output values B′, G′,
R′ is B′=1+12/15×(1-1)=1 G′=1+12/15×(16-1)=13 R′=1+12/15×(16-1)=13 ……(3) becomes. Therefore, blue B′ has the input value as it is,
Green G' and red R' are converted as values lower than the input value (actual signal level is higher), and are hard-copied according to the above-mentioned Y, M, C density table accordingly. As a result, the density relationship shown in FIG. 7 is satisfied. If you are dissatisfied with the color appearance of the hard copy due to different types of photosensitive materials, please refer to the above.
Just select and change the values of FB, FG, and FR in equation (1) appropriately.

Although we have explained the conversion on the CRT screen of a color TV,
Not limited to CRT screens, CRT images on displays in industrial measurement, or CRT
It can also be applied to color liquid crystal displays, etc., and can be applied to all cases where hard copies are obtained from these screens.

(Effects of the Invention) As described above, according to the method of the present invention, it is possible to reproduce colors that are colorful and have faithful reproduction of brightness simply by converting the image signal of a color TV or the like into a predetermined signal. Therefore, it is possible to provide a color signal conversion method that is extremely simple and has good characteristics.

[Brief explanation of drawings]

Figures 1, 5, and 7 are diagrams showing the relationship between density and signal level, Figure 2 is a diagram showing spectral density characteristics, and Figures 3, 4, and 6 are diagrams showing the relationship between color and saturation, respectively. A diagram showing the relationship between brightness,
FIG. 8 is a schematic diagram showing an embodiment of a device for realizing the present invention, FIG. 9 is a block diagram showing an example of a signal conversion circuit, and FIG. 10 is a diagram showing the relationship between input signal level and quantized signal. FIG. 11 is a diagram showing analytical density for converting a quantized signal into color density. 1... Signal conversion circuit, 2... Maximum input discrimination circuit, 3, 4, 5... Subtractor, 6, 7, 8... Density setter, 9, 10, 11... Adder.

Claims (1)

[Scope of Claims] 1. In a color signal exchange method for converting a color display image into a color hard copy, if the color reproduction ranges of the color display image and the color hard copy are different from each other, the blue B of the color display image, A color signal conversion method characterized in that green G and red R signals are respectively converted using the following formulas. B′=X ₀ +FB×(B−X ₀ ) G′=X ₀ +FG×(G−X ₀ ) R′=X ₀ +FR×(R−X ₀ ) ( _where , Maximum signal of R FB, FG, FR: Any positive number less than or equal to 1)