JPH04196676A - Method of estimating color - Google Patents

Abstract

PURPOSE:To obtain balance between lightness and saturation in an excellent way by deviating a hue of a peak of each color of an input side color cube in a direction of a peak of a color corresponding to an output side color cube in the case of compressing the saturation of the input side color cube. CONSTITUTION:The L* among a representing color system is converted in response to a spread ratio of the lightness on an achromatic color axis of an input side color cube and an output side color cube in relation to the direction of the lightness, the lightness of the input side color cube is compressed and mapped. In relation to the saturation direction, no conversion is implemented in the middle at a part where the color reproduction range of the input side color cube and the output side color cube and u*, v* or a*, b* among the value of the representing color system are converted in response to the spread of the saturation of the two color cubes in the circumference part and the saturation of the input side color cube is compressed and mapped. In this case, the hue of a peak of each color of the input side color cube is deviated in the direction of the peak of the color corresponding to the output side color cube. Thus, the lightness and saturation is excellent in the color reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color estimation method suitable for application to a color separation image correction apparatus used, for example, when reproducing a color television image into a color hard copy.

C. Background of the Invention When cocolor television images are reproduced on color hard copies, the respective color systems are different. That is, a color television image is constructed by an additive color method, and the R, G, B color system is used as the color system. On the other hand, in a color hard copy, a color image is constructed using a subtractive color method, and its color system includes, for example, Y, M,
The C coordinate system is used. In such a case, image data conversion, that is, color correction, is performed using these color systems.

For example, when reproducing a color television image on a hard copy, as shown in FIG. 16, red R1 green G1 blue B
image data is supplied to the color masking device 10,
This color masking device 1° outputs yellow Y, magenta M, and cyan C image data (color correction data), and this color correction data is supplied to the color printer 100.

Here, it is conceivable to refer to a lookup table to obtain color correction data from R, G, and B image data. As a method for obtaining color correction data to be stored in this lookup table, for example, Japanese Patent Laid-Open No. 63-2548
A method as described in Japanese Patent No. 64 has been proposed.

That is, R, G for a color television display.
, H image data combinations are displayed on the display, and the colors are measured to obtain the values of the color system.
Color patches based on each combination of M and C image data are output, and the colors are measured to obtain values in the same color system as for a color television display. Then, for each combination of R, G, and B image data of a color television image, using the values of the color system obtained by color patch colorimetry of the color hard copy, Y, M of the color hard copy that obtains the same or close value to the color system value obtained by colorimetrically measuring the color patch.

A combination of image data of C is obtained by interpolation calculation.

By the way, in general, color TV displays R, G,
The color reproduction range of the H image data is wider than that of the Y, M, and C image data of the color hard copy.

Therefore, 5. As mentioned above, the values of the color system obtained for the R, G, and B image data are directly converted to Y,
According to a method that determines Y, M, and C image data in correspondence with color system values for M and C image data, Y, M is used as R, G, and H image data.

When a color exceeding the color reproduction range of C image data is input, the corresponding Y, M, and C image data no longer exist.

In order to eliminate such inconvenience, R,G.

By compressing the color reproduction range based on image data of B, Y.

It is necessary to match the color reproduction range of both M and C image data.

As a conventional example, as described in, for example, Japanese Unexamined Patent Publication No. 63-254889, it has been proposed to compress the image by moving it in the direction of the achromatic axis while keeping the hue constant.

[Problem to be solved by the invention] However, in the conventional method of moving in the direction of the achromatic color axis while keeping the hue constant, since the hue is always constant, the amount of movement is determined depending on the external shape of the color solid. There was a problem in that the balance of saturation between hues shifted when moving.

For example, the solid line a in FIG. 17 is the color reproduction range of a television display, and the solid line a in the figure is the color reproduction range of a hard copy. A value x in the color reproduction range of the television display,
When y is moved, the hard copy color gamut value x', y' is compared to the difference in saturation of x, y,
'The difference in saturation becomes smaller, and the balance of saturation becomes unbalanced.

Furthermore, when reproducing a color television image consisting of the three primary colors R, G, and B into a color hard copy consisting of the three primary colors Y, M, and C, the color television image has R,
Among the 6 colors of G, B, Y, M, and C, R,
G.

The saturation of the three B colors tends to be high, whereas in color hard copies, R, G, B, and Y.

Among the six colors M and C, the saturation of three colors Y, M, and C tends to be higher. For this reason, for example, when a highly saturated B color in a color television image is moved within the color reproduction range of a hard copy with a constant hue, the saturation decreases significantly. As described above, there is a problem in that saturation decreases significantly for colors with high saturation on the armor color television image, and the balance of saturation between the entire colors shifts after movement.

Therefore, an object of the present invention is to enable good reproduction of brightness and saturation without shifting the overall balance of saturation between colors when reproducing a color television image with a color hard copy. Means for Solving Problem 11] In the color estimation method according to the first invention, the value of the color system for each combination of input color separation image information is determined, and the Calculate the value of the color system for each combination of image information.

The Lxu V-book color system or the L''a-book color system is used as the color system.

Then, among the color system values obtained for any combination of input color separation image information, L* is composed of the color system values obtained for each combination of input color separation image information. The achromatic color of the output color solid is composed of the difference between the maximum and minimum brightness values on the achromatic color axis of the input color solid and the color system values obtained for each combination of output color separation image information. Conversion is performed according to the ratio of the difference between the maximum and minimum brightness values on the axis.

Among the values of the color system obtained for any combination of input color separation image information, the U*, V wheel, or aL b wheel is expressed as the maximum chroma at the hue and brightness of the output color solid at that time. If the saturation is smaller than a times the brightness value (a < 1.0), no conversion is performed, and if the saturation is a times the maximum saturation value at the current hue and brightness of the output color solid, the output is The inner surface of the output side color solid is composed of a times the maximum saturation value of each hue and lightness of the side color solid, and the output side color solid is composed of the maximum saturation value of each hue and brightness of the output side color solid. For the part surrounded by the outer surface,
The entire portion surrounded by the inner surface of the output color solid and the outer surface of the input color solid formed by the maximum saturation values of each hue and lightness of the input color solid is converted so that they correspond to each other continuously.

As a method for this correspondence, when the saturation decreases, the hue determined from an arbitrary combination of input color separation image information is determined by the blue, green, and red of each color in the input color solid.

When entering a predetermined range before and after the hue of any of the six maximum chroma points of yellow, magenta, and cyan, the direction of the hue of the maximum chroma point of the color of the output color solid that is the same as the color corresponding to that hue. Decide to shift the hue.

Then, using the color system values obtained for each combination of the plurality of output color separation image information, the same value as the above-converted color system value for any combination of input color separation image information is calculated. Find a combination of output color separation image information to obtain.

According to the color estimation method according to the second invention, when the three primary colors of the input color separation image information and the three primary colors of the output color separation image information occur, the color specification for each combination of the plurality of input color separation image information is provided. At the same time, the values of the color system are determined for each combination of a plurality of output color separation image information.

As a color system, the Lhon U East V stock color system or the L Car A Car Fu color system is used.

Then, L values of the color system obtained for any combination of input color separation image information are made up of the color system values obtained for each combination of input color separation image information. The achromatic color of the output color solid is composed of the difference between the maximum and minimum brightness values on the achromatic color axis of the input color solid and the color system values obtained for each combination of output color separation image information. Conversion is performed according to the ratio of the difference between the maximum and minimum brightness values on the axis.

For any combination of input color separation image information, 5 of the values of the color system obtained for U, V, or A are determined by the hue and brightness of the output color solid at that time. a times the maximum saturation value (if it is smaller than a<1.0>, no conversion is performed, and if the saturation is more than a times the maximum saturation value at the hue and brightness of the output side color solid) , the inner surface of the output color solid, which is composed of a times the maximum saturation value of each hue and lightness of the output color solid, and the output color, which is composed of the maximum saturation value of each hue and brightness of the output color solid. For the part surrounded by the outer surface of the solid,
The entire portion surrounded by the inner surface of the output color solid and the outer surface of the input color solid formed by the maximum saturation values of each hue and lightness of the input color solid is converted so that they correspond to each other continuously.

As a method of association, when saturation decreases, the hue found from any combination of input color separation image information falls within a predetermined range before and after any of the hues at the maximum saturation point of the three primary colors in the input color solid. In this case, it is determined to shift the hue in either direction of two of the hues at the maximum saturation points of the three primary colors in the output side color solid that come before and after on the hue wheel.

Then, using the color system values obtained for each combination of the plurality of output color separation image information, any combination of input color separation image information has the same value as the above converted color system value. Find a combination of output color separation image information to obtain .

[Function] In the first method of the invention, each combination of input color separation image information is adjusted in accordance with the ratio of the spread of brightness on the achromatic color axis of the input side color solid and the output side color solid in the brightness direction. Among the values of the color system obtained for this, LX is converted, and the brightness of the input color solid is compressed and mapped.

Regarding the saturation direction, the central part of the overlap between the color reproduction ranges of the input color solid and the output color solid is not converted, and at the edges, the input color separation is performed according to the spread of the saturation of the two color solids. Of the color system values obtained for each combination of image information, U*, 7 or 8 quintillion, b* are converted, and the saturation of the input color solid is compressed and mapped.

Furthermore, when the saturation of the input color solid is compressed and mapped, the hue is shifted so that the peak of each color in the input color solid is shifted in the direction of the peak of the corresponding color in the output color solid.

This allows the color reproduction range on the input side to fall within the color reproduction range on the output side while balancing the overall saturation through natural conversion, and the color reproduction based on the required output color separation image information is The color saturation will be good, and the overall color saturation will be well balanced.

In the second invention method, three primary colors, for example, R, G, B, of input color separation image information and three primary colors of output color separation image information are used.
When primary colors, for example Y, M, and C, are present, when the saturation of the input color solid is compressed and mapped, the peaks of the three primary colors of the input color solid are the same as the peaks of the three primary colors of the output color solid. The hue is shifted in the direction.

Although this causes a shift in hue, the overall saturation is balanced.

[Embodiment] Hereinafter, six embodiments of the present invention will be described with reference to the drawings. In this six embodiments, for example, colors reproduced on a television display by each combination of R, G, and B image data are Y, M, C, for reproduction in printing
This is to obtain a combination of image data of K (shades).

In addition, here, R, G, B, Y, M, C,
The explanation will be given assuming that the value of K is a value of 0 to 255.

■First, color patches based on each combination of R, G, and B image data are displayed on a TV display, and the values of the x, y, and z color systems are determined, and then L pieces, one piece, and ■ Find the value of this color system.

In this case, for example, R connected to a TV display,
Using a device that can write R, G, and H image data into frame memories of 8 bits each for G and B using a computer and display the colors on a television display, the method shown below (Method 1) or (Method-2)
Find the values of the x, y, z color system by:

(Method-1) For each of R, G, and B image data, 0°64
．． 5 quantization levels of 128, 192.255 are taken, and the color by each combination of these (5xsx5=125
) on a television display one color at a time, and each color is measured using a spectroradiometer to determine the values of the x, y, z color system.

Here, by interpolating the middle of 5X5X5=125, 9X
It was set to 9X9=729. Although 9X9X9=729 colors may be measured, the number of measurements increases.

(Method-2) Known as the color reproduction formula for television displays,
The values of the x, y, z color system may be calculated by applying the following basic formula.

Here, XR, XG, XB, YR, YG,
YB.

In order to determine the coefficients of ZR, ZG, ZB and γ according to the characteristics of the TV display used, RlG, H
1 between quantization levels from 0 to 255 for each single color.
Take about 0 to 20 points and measure the color displayed on the TV display using a spectroradiometer to determine the x, y, and z values, and then calculate the R, G, BLX, and Y values.

The value of each coefficient is determined from the relationship between the Z values.

Thus, X for 9X9X9=729 colors by (Method-1) or (Method-2).

Find the values of the Y and Z color systems. And this x,
y.

Using the values of the two color systems, calculate the values of L', u book, and ■ book color system. For Xn, Yn, and Zn, standard light D65 x,
Apply x, y, and z such that y.

The relationship between x, y and X, Y, Z is as follows.

x=X/ (X+Y+Z) y=Y/ (X+Y+Z
) D65 x and y values, x=0. 3127,
Since y=0.3290, Xn, Yn, and Zn satisfy the following formula.

Xn / (Xn + Yn + Zn) = 0. 31
27Yn/ (Xn +Yn +Zn)=0.329
0 Here, we have to determine the levels of the absolute values of Xn, Yn, and Zn, but in order to match the levels of the measured values of x, y, and z,
55) When displaying 17) X, Y, 217)
Yn was made approximately equal to the value Y.

In this way, the values of Lkyo, U*, ■* color system are changed to R, G
, are determined for 9X9X9=729 colors based on the image data of B. Let the values of these L", U book, V" color system be L car TVI (R, G, B) U car TVI (R, G, B) V book TVI (R, G, B). The figure shows these values in the L-line, U-line ylK color system, which will hereinafter be referred to as the color solid of a television display.

■Next, color patches based on each combination of Y, M, and C image data are measured, and the values of the x, y, and z color systems are determined, and then L, u, and v
*Calculate the value of the color system.

In this case, for each of Y, M, and C image data, 0. 64. 128. 192. 255 quantization levels are taken, and a color patch of each combination of these colors (5x5x5=125) is created.

At this time, for each combination of Y, M, and C image data, K image data is determined using the following relational expression, and that amount of smear is added to the color patch based on the Y, M, and C image data. Add K.

K = 1.6 (min[Y, M, C] -128)
-(1) However, if X<O, then = 0 Actually, 4 images of Y, M, C, and K of Y (5x5x5) M (5X5X5) C (5x5x5) K (5X5X5) are plated. Printed on 4 sheets of black and white film using a scanner, based on which Y,
Printed on 4 printing plates M, C, K, Y, M
.

Printing is performed using the usual plate-making printing process of printing from the printing plate with four color inks of C and K to create 5 x 5 x 5 = 125 color patches.

Then, measure this color patch with a colorimeter, x,
Calculate the y, z color system and values, and then calculate the value.

Calculate the values of g book, y car color system.

Here, by interpolating the middle of 5X5X5=125, we get 9
X 9 x 9 = 729. 9X9X9
Colorimetry may be performed by printing color patches of =729 colors, but this increases the number of measurements.

In this way, the values of L, u”, and v car color systems are changed to Y,
9X9X9=72 based on M, C, K image data
Find out about 9 colors. Let the values of this Lx, u*, v* color system be L book IN (Y, M, C) u” IN (Y, M, C) V book IN (Y, M, C), Figure 2. This value is shown in this color system as Lt, u5.Hereinafter, this will be referred to as the color solid of printed matter.

(2) Next, find the maximum and minimum values of Lm from the color solid values of the television display.

In this case, among the 9X9X9=729 colors, a combination with the maximum L car and a combination with the minimum LX are found, and the L car at that time is found.

“Maximum value” is the value of L when displaying white with R=G=B=255, and is defined as L” TVlmax.

- "Minimum value" is the value of LX when black is displayed with R-G=B=O,
L”TVI■in.

(2) Next, calculate the maximum and minimum values of L ky from the color solid values of print '.

In this case, a combination with the maximum number of L colors and a combination with the minimum number of LX are found among 9x9x9=729 colors, and then the L colors are found.

"Maximum value" Y = M = C = 0 (K = O) and the value of * on a white background, L books IN■ ax.

“Minimum value” is the value of LX when black is printed with Y=M=C=255 (K=203), and is defined as L ” lNm1n.

■Next, the value book TVI of color solidity of TV display,
U book TVI, v car TVI will be released on Lkyo TV2.
u ” TV2° Convert to V car TV2.

That is, linear conversion is performed as shown in the following equation so that the maximum and minimum values of the L color solids of the television display become the maximum and minimum values of the L color solids of the print.

X (L car TVI-L car TVLg+in) +L car I
In addition, u books and y MK are also converted as shown in the following equation.

■Next, create a printout of a gray stage chart with Lm equally spaced.

In other words, U books, V books = O, and L books are 20 to 100.
A gray stage chart is created that has a range of 5 quantization levels and an interval of 5 quantization levels (see Figure 3).

In this case, the value of the color solid of the printed matter L”IN(Y, M.

C), u car IN (Y, M, C), v' I
N(Y, M.

C), find the values of Y, M, and C at each step of the gray stage chart by convergence operation.

Here, the convergence calculation will be explained. In this case, the value of the color solid for each step of the gray stage chart is given as target value T' to the color solid of the printed product (illustrated 20th).

For the sake of simplicity, the description will be made assuming that there are two basic colors (for example, Y and M).

Figure 4 shows the Y and M coordinate system. When each lattice point is mapped to the L*, u*, y color system by the above-mentioned process (2), the result shown in FIG. 5 is obtained. The vertices B, C, G, and F of the square in FIG. 4 correspond to B', C', G', and F' in FIG. 5, respectively.

First, L'', ukyo for each step of the printed matter.

The value of this color system is given as the target value T' (see FIG. 5).

In this case, when the target value T' is within the area surrounded by grid points a' to d' as shown in Fig. 5, the combination of Y and M in the Y and M coordinate system (target value T) ,
As shown in the fourth rM, it is estimated to be within the region surrounded by lattice points a to d.

Then, where the target value T is located in the area formed by the grid points a % d is determined by performing a convergence calculation while associating the color system shown in FIG. 5 with the coordinate system shown in FIG. 4 . Although the conversion from the coordinate system shown in Figure 4 to the color system shown in Figure 5 is known for performing convergence calculations in this way, the reverse conversion is very complicated and there is still no good conversion. This is because the formula is not known.

First, it is determined in which region the target value T' is located among a plurality of regions formed by 81 grid points (see FIG. 5). As shown in FIG. 7, when in the area SO',
As shown in FIG. 6, the target value T is estimated to be in an area SO corresponding to the area SO'.

Next, the estimated area SO is equally divided into four areas 81 to S4. The five division points e to i are calculated by weighted averaging using surrounding grid points that have already been determined. Then, the values corresponding to this dividing point e~1 are L*, U East, ■ The values obtained when converted to this color system are plotted on the color system shown in Figure 7, and the plotted dividing points e'~ In which region is the target value T set among the four regions 81' to S4' formed by i'?
′ is found. When the target value T is in the region 82' as shown in FIG. 7, the target value T is in the region S2 as shown in the sixth section.
' is estimated to be in the area S2 corresponding to '.

Next, the estimated region S2 is equally divided into four regions 85 to S8. The five division points j-n are calculated by weighted averaging using the surrounding grid points and division points that have already been determined. Then, the value corresponding to this division point j~n is L*
, u *, y The values obtained when converted to this color system are plotted on the color system shown in Figure 7, and four areas S5' to S8 are formed by the plotted division points j' to n'.
' in which area the target value T' is located is determined. 7th
When the target value T is in the region S8' as shown in the figure, it is estimated that the target value T is in the region S8 corresponding to the region 88' as shown in FIG.

Next, the estimated region S8 is equally divided into four regions 89 to S12. The five division points 0 to S are calculated by weighted averaging using the surrounding grid points and division points that have already been determined. Then, the value corresponding to this dividing point 0 to S is L
Book, u *, y The values obtained when converted to the book color system are plotted on the color system in Figure 7, and the four areas S9'' to S1 formed by the plotted division points 0' to S' are plotted.
2', in which region the target value T' is located is determined. When the target value T is in the area 810' as shown in FIG. 7, the target value T is in the area S corresponding to the area 810' as shown in FIG.
It is assumed that it is in the IO.

By repeating this region division, the grid becomes smaller and smaller until it finally converges. Then, the target value T is obtained by averaging the four grid points or division points forming the converged area.

In addition, for Y, M, and C at each step obtained by the convergence calculation described above, (1)
Find the value of K using the formula.

Then, the Y, M, C, and K image data obtained at each step as described above are printed through a prepress printing process to create a gray stage chart.

(2) Next, a gray scale chart in which Lm is equally spaced is displayed on the television display.

In other words, U*, V book; 0, Lm is 20 to 10
A gray scale chart is displayed with a range of 0 and an interval of 5 quantization levels (see Figure 3).

In this case, L TV2 (R
, G, B), u Hon Ding V2 (R,
Using the car TV2 (R, G, B), find the values of R, G, and B at each step of the gray stage chart by convergence calculation.

Then, a gray level chart is displayed on a television display from the R, G, and B image data obtained at each step as described above.

Next, compare the gray stage chart on the TV display with the gray stage chart on the printed version to see if the boundaries of each step in the chart on the TV display can be determined in the same way as on the printed chart. Make sure that the color of the TV display is not the same as the 3D Lm, as follows.

U*, ■Convert values in this color system.

X (L car TV2max -L” TV2i+in)
+ Change the value of constant γ at L car TV 2 min.
Book TV3. u”TV3. Recalculate to v”TV3,
■Operation L"TV2゜u" TV2. v' TV
2 instead of L'TV3. U-book TV3°Use the V-car TV3 and compare again with the printed chart.

Then, repeat the above operations ① and ②, and then set L car TV 3. u car tv3. v' TV3 will be used in the following +71 operation.

0th order, Y for each combination of R, G, B.

Find the combination of M, C, and K (color correction data).

In other words, each color combination of R, G, and B (32x
32x32=32768), U*.

■Value L' of this color system TV3. u” TV3.
Find v' TV3. Then, this value is given as the target value T' to the color solid of the printed material (shown in Figure 2), and Y, for each combination of R, G, and B is determined by convergence calculation.
M.

Find the value of C.

At this stage, since the color reproduction range of the printed matter is narrower than that of the television display, the target value T' may be outside the color reproduction range of the printed matter. Example 2] converts the target value T' to within the color reproduction range of printed matter, and then performs convergence calculation to convert Y, M
, find the value of C.

[Example 1] LmTV found for each combination of R, G, and H
3. u car tv3. The value of v book TV3 is given to the color solid of the printed matter (shown in FIG. 2) as the target value T~.

At this time, the value of L wealth, U*, ■* is 1, and each is L*T
#, U car T'', V car T''.

Also, the saturation value found by u”T′2+v T′2 is r
T=, arctan (v ” T#/u ” T″)
When the hue angle determined by is θT″, its L″TV3,
The maximum value of saturation r I of the color solid of the printed matter at θT''
A saturation value r lNa1dT'' which is 8 times (a<1.0), for example, approximately 2/3 times NmaxT'' is set as a threshold value (see FIG. 8).

If rT" is less than r lNm1dT", without conversion, L car T'=L"T", U car T'=ukyoT'',
V book T'=v book T'', rT'=rT'', θT'=θ
Let it be T''.

Further, when rT'' is larger than r lNm1dT~, rT' etc. are set as follows according to θT''.

The hue angle θ is as follows: θ = 0° ... U axle top stop θ = 90° ... V axle top stop θ = 180° ・ ・ ・ U axle top stop θ = 270°
・・・V main axis top negative θ=360″″ ・・・When U axle is set to top stop (see Figure 9), 120°≦θT″≦17
When 0° is not satisfied, L” T' = L” T
″, θT″ = θT″, and rT′ as shown in the following equation.

X (r T= -r lNm1dT") + r
lNm1dT"In this formula, r TVmaxT",
This is the maximum value of the saturation of the color solid of the TV display in the L car TV3, θT'' (see FIG. 8).

For U car T' and V car T', θT'=θT'', and r
T' is a value that satisfies the above equation.

Next, when 120°≦θT″≦170° is satisfied, θT″ is first converted into θT″2 using the following equation.

Here, 131° is the hue angle of the maximum chroma point of G (green) in the color solid of the TV display (see Figure 1).
, 147° is the hue angle of the maximum saturation point of G (green) in the color solid of the printed matter (see Fig. 2).

120° ≦θT″ ≦131°, θT” 2 becomes.

At 131'<θT#≦170°, θT “2 becomes.

As a result, L book T' = L book T'', θT' = θT''2
At the same time, let rT' be as shown in the following equation.

X (rT″-r lNm1dT″2> +r lNm
1dT"2 In this formula, r INmaxT"2 is L vehicle weight", the maximum value of the saturation of the color solid of the printed matter at θT"2, r lNm1dT"2 is the saturation value obtained by multiplying r INmaxT-2 by 8, r TVmaxT" 2 is L"T", θ
T″2 is the maximum value of the saturation of the color solid of the television display.

In addition, for U and V cars, θT' = θT" 2,
And rT' is a value that satisfies the above expression.

As mentioned above, L-car T'', U-car T'', and V-car T'' are converted into L-kyo T', u''T', and v-car T',
Both fall within the color reproduction range of printed matter.

The maximum value of saturation is determined as follows.

Only the values of the combination forming the outer surface of the color solid are used, which are converted into lightness LX, saturation r1, and hue θ. By the way, there are eight faces that become the outer faces of the color solid, Y and M.

It is a surface in which C or B, G, and R are all O or maximum. Then, the position on the grid that includes the hue θ and brightness wheel is found, and the weighting is determined by averaging the saturation values of the four points around it.

In this way, the L books T', u*T', and v''T' found for each combination of R, G, and B are given as the target value T' to the color solid of printed matter (shown in Figure 2), and the convergence is By calculation, Y, M, and C are obtained.The convergence calculation is the same as that explained in FIGS. 41!1 to 7, so the explanation will be omitted.

[Example 2] LXTV found for each combination of R, G, and B
3. The value of u''TV3.vTv3 is given to the printed color solid (shown in FIG. 2) as the target value T'.

Let the values of the wealth u* and y vehicle at this time be L*T~, UmotoT", and v*T", respectively.

In addition, the saturation value found by u T"'+v*T" is rT", arctan (v *T"/UkyT")
When the hue angle determined by is θT'', its L*TV3,
Maximum saturation value r IN of the color solid of the printed matter at θT″
A saturation value rIN@idT'' obtained by multiplying maxT'' by 8 times (a<1.0), for example, about 2/3, is set as a threshold value (see FIG. 8).

rT'' is less than rlN■idT''lNm1dT'' Without conversion, L*T'=L'T'', u*T'=u''T-1V
KyoT'=vKyoT'', rT'=rT'', θT'=θ
Let it be T''.

Further, when rT'' is larger than r fNmidT'', rT' etc. are set as follows according to θT''.

When 2001≦θT″≦300° is not satisfied,
Let L book T' = L book T'', θT' = θT'', and
Let rT′ be ′ as shown in the following equation.

X (r T# -r lNm1dT") + r
lNm1dT#With this formula, r ding■wearaxT'',
This is the maximum value of the saturation of the color solid of the TV display at θT~ for the L TV3 (see FIG. 8).

u"T', V zero T', θT' = θT", krT'
is a value such that the above formula is satisfied.

Next, when 200m≦θT″≦300@ is satisfied, θT− is first converted into θT″2 using the following equation.

Here, 266° is the hue angle of the maximum chroma point of B (cyan) in the color 3D of a television display (1st library), 234° is the maximum chroma of C (cyan) in the color 3D of printed matter. This is the hue angle of a point (see Figure 2).

2666 ≦θT″ ≦300 @ in θT#2 becomes.

200°≦θT″<266’r, θT#2 becomes.

As a result, L*T'=L*T", θT' = θT~2
At the same time, let rT' be as shown in the following equation.

X (rT″ −r lNm1dT″ 2) +
r lNm1dT″ 2In this formula, r INmax
T″2 is the maximum value of the saturation of the color solid of the printed matter for L book T″, 6th book″2, r lNm1dT″2 is r INma
Saturation value xT” 2 times 8, r TVmaxT= 2
is the maximum value of the saturation of the color solid of the television display at L vehicle weight ", θT" 2.

Note that for U* and V, θT' = θT''2, and rT' is a value such that it satisfies the above formula.

As mentioned above, L'T', u book T', and v book T' converted from L"T", u"T", and v"T" all fall within the color reproduction range of the printed matter. become.

In this way, the L-line T', u-line T', and v-line T' found for each combination of R, G, and H are given as the target value T' to the color solid of printed matter (shown in Figure 2), and the convergence Find Y, M, and C by calculation. Since the convergence calculation is the same as that explained in FIGS. 4 to 7, the explanation will be omitted.

In this way, Y for each combination of R, G, and H determined by [Example 1] and [Example 2].

For each combination of M and C, find K using equation (1).

This allows Y for reproducing colors by each combination of R, G, and B, for example, in color printing.

A combination of M, C, and K is required.

In this example, in the brightness direction, R, R,
Of the color system values obtained for each combination of G and B, the L wheel is converted, and the brightness of the color solid of the television display is compressed and mapped. In addition, regarding the direction of saturation, the color solidity of the TV display (input) and the printed matter (output)
There is no conversion in the central part of the overlapping part of the color solids, and in the surrounding area, R, G is converted depending on the spread of saturation of the two color solids.
, B of the color system values obtained for each combination are converted, and the saturation of the color solid of the television display is compressed and mapped. As a result, the color reproduction range of the TV display falls within the color reproduction range of printed matter with a natural conversion result, and the required Y, M, C,
The combination of K results in good color reproduction, brightness, and saturation.

In addition, when the saturation of the color solid of the television display is compressed and mapped, the G (green) peak of the color solid of the television display is in the direction of the G peak of the color solid of printed matter, or the color solid of the television display is Since the hue of the B (blue) peak is shifted in the direction of the C (cyan) peak of the color solid of the printed matter, the overall saturation is balanced.

In addition, in [Example 2] of the above-mentioned example, the peak of B (blue) of the color solid of the TV display is the peak of C of the color solid of the printed matter.
Although the hue is shifted in the direction of the (cyan) peak, it may be shifted in the opposite direction, in the direction of the M (magenta) peak.

In addition, in [Example 1] and [Example 2] of ■ of the above embodiment,
Although the hue range in which each hue is shifted is only one region, it may be multiple, and the two examples [Example 1] and [Example 2] may be used in combination.

Further, in the above embodiment, the brightness is kept constant when the saturation is changed, but the brightness may be changed as the saturation is changed.

Further, in the above embodiments, the L car U car V car color system is used, but the L"a"b color system may also be used.

Next, the color correction data (Y,
A color masking device configured to store color data (M, C, K) in an LUT (look-up table) in advance and compare the color correction data with input image data (R, G, B) will now be described.

In this case, if Y, M, C, and K image data corresponding to all R, G, and B image data are stored in the LUT, the capacity of the LUT becomes enormous.

Therefore, in order to discuss with the applicant the reduction of memory capacity,
The color space formed by R, G, and B image data is divided into multiple basic grids, and LLIT has the Y, M, C, and K colors for the combination of R, G, and H image data located at the vertices. Store image data, R, G
, Y and M for the combination of image data of H
, C, K image data does not exist, by the weighted average of the Y, M, C, K image data of the vertices of the basic grid that includes the R, G, B image data (interpolation points). We proposed to obtain Y, M, C, and K image data.

For example, as shown in Fig. 10, when there is an interpolation point P in the basic grid consisting of vertices A-H, the The volume of the rectangular parallelepiped is Y, M, C, with vertices A to H.
It is used as a weighting factor for K image data.

That is, the vertices A~ of the basic lattice that include this interpolation point P
The image data of Y, 'M, C, and K of H is Yi.

Mi, Ci, Ki (i=1 to 8), Y of vertices A to H
, M, C, K, Y, M at the interpolation point P, if At (i=1 to 8) is the weighting coefficient for the image data.

ρ for the C, K image data Yp, Mρ, Cρ is calculated by the following equation.

Yρ=(1/SiAi)SiAiYiMp='(1/
ΣAi) ΣAi Mi Cρ=(1/SiAt)SiAi C1 Kp=(1/SiAi)SiAi Ki...ku2) In such an interpolation process, Y, M, C of the interpolation point
.

When calculating ρ for K image data yp, MP, and Cρ, eight multiplication and accumulation processes are required for each.

We proposed to the applicant an interpolation process that can reduce the number of times this multiplication and accumulation process is performed.

As shown in FIG. 11, a total of six pentagonal pyramids are formed by one-dot chain lines for the basic lattice composed of vertices ASH. When the coordinates of the interpolation point P are (5, 1°2), this interpolation point P is located at the vertices A and B as shown in FIG.
It can be seen that it is included in the pentagonal pyramid T formed by , C, and G.

Once the pentagonal pyramid T is determined, the interpolation point P is then connected to the vertices A, B, C, and G, as shown in Figure 12.
A total of four new pentagonal pyramids are formed, each with a volume V
BCGP, V ACGP, V ABGP,
V ABCP is required. These volumes and vertices A,
B, C, G's Y.

M, C, K image data YA-YG, MA-MG.

From CA~CG, ni^~KG, Y of interpolation point P.

M, C, K image data Yp, Mp, Cp
, Kp is calculated by the following formula (VABCG
is the volume of the pentagonal pyramid T.

Yρ= 1 /VABCG (VBCGP-Y＾VA
CGP-YB 10vABGP・YC+VABCP-ya
>Mp=1/VABCG(VBCGP-MA+
VACGP-MB 10VABGP・MC+VABCP-
MO)Cp=1/VABCG(VBCGP-C
A10V, ACGP-CB +VABGP= CC+V
ABCP-CG)Kp=1/VABCG(
VBCGP-KA+ VACGP-KB +VAB(
iP-KC+VABCP-KG)... (3) If the coordinates of the interpolation point P are correct, the triangle jIT to be used will also be correct. For example, if the coordinates of the interpolation point P are P(3,1
, 5), this interpolation point P is included in the pentagonal pyramid T formed by the vertices A, C, D, and G, so 5 This pentagonal pyramid T is used. Ru.

In this way, in the interpolation process using the pentagonal pyramid, the Y, M, and C of the interpolation points are determined by four multiplication and accumulation processes.

It is possible to calculate K image data yp, Mp, cp.

FIG. 14 shows an example of a specific configuration of a color masking device.

In the same figure, reference numeral 20 denotes a color correction data storage means, and a lookup table (ML
UT) 21Y to 21K, Y, M, respectively.
C and K color correction data are stored.

By the way, for MLtJT21Y~21, for example, a ROM with a 256-bit capacity is used, and R, G,
Only 32 points between the minimum level and the maximum level of the image data of B are extracted, and 32X32X32=32768 points of image data are stored in each of the MLUs 721Y to 21.

In this case, the R, G, and H image data are 8 bits and have 256 gradations, and are divided into 32 points, starting from 0, for example, and divided into "8" increments. 16.
..., 240. The 33rd point, 249 to 255, is either not used or treated as 248.

Y, M of each such distribution point, that is, the vertices of the basic lattice whose basic lattice spacing is 8 quantization levels.

The image data of C and K is calculated as described above, and the calculated image data is MLUT21Y to 21KG:
Stored.

Further, 60 is a look-up table (WLUT) constituting a weighting coefficient storage means, and the WLUT 60 stores weighting coefficients corresponding to each interpolation point.

In the case of interpolation processing using a cube, when the basic lattice spacing is 8 quantization levels as described above.

The total of the eight weighting coefficients is 8x8x8=512, which is normalized to 256. In addition, so that an 8-bit general-purpose IC can be used as the WLUT 60, the maximum value of the weighting coefficient is set to 255. For example, if the interpolation point P is at the same position as the vertex A in Fig. 10, the weighting coefficient P1 to P8 are as follows.

PL, P2. P3. P4. P5. P6.
P7. P8255, 0, 0, 0
, O, O, 0, 1 (512, 0, 0, O, O, 0
, 0, 0), and the sum of the weighting coefficients is always 256.

In addition, in the case of interpolation processing using a pentagonal pyramid, when the basic grid spacing is 8 quantization levels as described above, the sum of the four weighting coefficients is 8x8x8/6=5 1 2/6 is normalized to 256.

In addition, so that an 8-bit general-purpose IC can be used as the WLUT 60, the maximum value of the weighting coefficient is set to 2558.For example, if the interpolation point P is at the same position as the vertex A of the 11th section, the weighting VBCGP.

V ACGP, V ABGP, and V ABCP are as follows.

V BCGP, V ACGP, V ABGP,
V ABCP255, 0. 0. 1 (512/6. 0, 0, O), and the sum of the weighting coefficients is always 256.

A look-up table (PLUT) 41 constituting the address signal forming means 40 is used for R, G, and B image data.
This PLUT41R is supplied to R~41B.
-41B are supplied with signals for the distribution from the controller 50.

PLUTs 41R to 41B output 5-bit address signals corresponding to the upper 5 bits of R, G, and B image data (representing the reference point of the vertex of the basic lattice that includes point III P). 21K.

In the case of interpolation processing using a cube, eight vertices of the basic lattice including the interpolation point P are M based on the distribution second signal.
Five-bit address signals are sequentially output as specified in LUTs 21Y-21.

In the case of interpolation processing using a pentagonal pyramid, the distribution is based on the signal, and the four vertices of the pentagonal pyramid that include the interpolation point P are M
Five-bit address signals are sequentially output as specified in LUTs 21Y-21.

Y, M output by MLU721Y~21.

The C and K image data are respectively supplied to multipliers (MTL) 31Y to 31K constituting the multiplication/integration means 30.

Also, R and G from PLUT41R to 41B.

The lower three bits of the image data of B (representing the position of the interpolation point P in the basic grid) are output as a weighting coefficient designation signal, and this weighting coefficient designation signal is supplied to the WLUT 60. The WLUT 60 is supplied with a signal for the distribution from the controller 50, and weighting coefficients for the distribution are sequentially output based on the signal.

In the case of interpolation processing using a cube, the eight weighting coefficients P1 to P are sequentially specified in MLtJT21Y to MLtJT21 to correspond to the eight vertices of the basic lattice that includes the interpolation point P.
8 are output sequentially.

In the case of interpolation processing using a pentagonal pyramid, the four weighting coefficients are sequentially specified as the four vertices of the pentagonal pyramid containing the interpolation point P are sequentially specified in MLUT21 Y~21. Output.

The weighting coefficients output from WLUT60 are MTL31Y~
Supplied to 31K. And this MTL31Y~31
Then, Y output by MLUT21 Y~21
, M, C, K image data (8 bits), and W
Multiplication with a weighting coefficient (8 bits) from LUT 60 is performed.

The multiplication outputs of the upper 8 bits of the MTLs 31Y to 31 are supplied to accumulators (ALUs) 32Y to 32K, respectively, for addition processing. A reset signal is supplied from the controller 50 to the ALUs 32Y to 32K.

In the case of interpolation processing using a cube, addition processing is performed sequentially corresponding to the eight vertices of the basic lattice that includes the interpolation point P, and each time the result is latched by a latch circuit described later. will be reset.

In the case of interpolation processing using a pentagonal pyramid, addition processing is performed sequentially corresponding to the four vertices of the pentagonal pyramid that includes the interpolation point P, and each time the result is latched by a latch circuit described later. will be reset.

As mentioned above, the sum of 8 weighting coefficients in the case of force interpolation processing using a cube and the sum of 4 weighting coefficients in the case of interpolation processing using a pentagonal pyramid is 256. In this example, MTL 31 Y~3
The upper 8 bits of the multiplication output by 1 are used, so-called 8
Since a bit shift is performed, this results in 1/Ai in equation (2) and 1/V in equation (3).
ABCG processing will be performed.

The outputs of the ALUs 32Y to 32 constituting the multiplication/accumulation means 30 are supplied to latch circuits 71Y to 71K, respectively. This latch circuit 71Y to 71K has a controller 50.
A latch pulse is supplied.

In the case of interpolation processing using a cube, the results of sequential addition processing corresponding to eight vertices of the basic lattice including the interpolation point P are latched.

In the case of interpolation processing using a pentagonal pyramid, the results of sequential addition processing corresponding to the four vertices of the pentagonal pyramid where the interpolation point P is included are latched.

Therefore, from the latch circuits 71Y to 71K, in the case of interpolation processing using a cube, the equation (2) is shown, and in the case of the interpolation processing using a pentagonal pyramid, the equation (3) is shown. Y, M of interpolation point P.

C and K image data are output.

In Fig. 15, the image data of K is not stored in the lookup table in advance, but after the color masking device (A in the same figure) that outputs the image data of Y, M, and C, K is
1) This is an example of adding a device (section B) that calculates and outputs using formula. According to this example, memory capacity can be saved. In this figure, parts corresponding to those in FIG. 14 are denoted by the same reference numerals, and detailed explanation thereof will be omitted.

In the figure, Y, M, and C image data output from latch circuits 71Y to 71C are supplied to a minimum value detection circuit 81, and the minimum value among Y, M, and C, that is, sin [Y, M, C] is detected. Then, the detected sin [Y, M,
C] is supplied to a lookup table 82, and this lookup table 82 outputs image data of K determined by the following relational expression.

K=1.6 L* of the color system values obtained for each combination of input color separation image information is converted according to the ratio of the brightness spread on the achromatic color axis of the input side color solid and the output side color solid. , the brightness of the input color solid is compressed and mapped. Regarding the saturation direction, the central part of the overlapping color reproduction range of the input color solid and the output color solid is not converted, and the peripheral part is converted by 2.
Among the values of the color system obtained for each combination of input color separation image information according to the spread of saturation of the two color solids, U*
, 7, 3, or 5 are converted, and the saturation of the input color solid is compressed and mapped. Furthermore, when the saturation of the input color solid is compressed, the peak of each color in the input color solid is shifted in hue in the direction of the peak of the corresponding color in the output color solid. Therefore, the color reproduction range on the input side falls within the color reproduction range on the output side while balancing the overall saturation through natural conversion, and the required output color separation image information is based on brightness, color reproduction, The color saturation can be made good, and the overall color saturation can be well balanced.

[Brief explanation of the drawing]

1 to 9 are diagrams for explaining the color estimation method according to the present invention, FIGS. 10 to 13 are diagrams for explaining the interpolation process, and FIGS. 14 and 15 are diagrams for explaining the color masking device. 16 and 17 are diagrams for explaining the conventional method. 1o...Color masking device 100...Color printer Fig. 8 V* Fig. 9 Target [T Y, M No. L2025 ......
・・・・・・・・・ 95 100U zero 0 0
・・・・・・・・・－・・・・・・・・・－・・・－・・・
・・・ 0 0V$ 0 0 ・・・・・・・・・
・・・・・・－・・−・−・・・・・ 00 Play stage chart Fig. 3 0 Assignment of saturation target value T' Fig. 5 SL Y, M coordinate thread Fig. 6 81' Brightness 3J Color display Figure 7

Claims (2)

[Claims] (1) Find the value of the color system for each combination of a plurality of input color separation image information, find the value of the color system for each combination of a plurality of output color separation image information, and calculate L^ as the color system. *u^*v^*Color system or L^
Using the *a^*b^* color system, L^* of the values of the color system obtained for any combination of the above input color separation image information is calculated for each combination of the above input color separation image information. The difference between the maximum and minimum brightness values on the achromatic color axis of the input color solid, which is composed of the values of the color system determined for , and the table determined for each combination of the output color separation image information. It is converted according to the ratio of the difference between the maximum value and the minimum value of brightness on the achromatic color axis of the output color solid composed of color system values, and the obtained value is obtained for any combination of the above input color separation image information. Among the color system values u^*, v^* or a^*,
b^* is the hue of the output side color solid whose saturation is above,
If the saturation is smaller than a times the maximum saturation value at lightness (a < 1.0), no conversion is performed, and the saturation is at least a times the maximum saturation value at the hue and lightness of the output color solid at that time. In the case of The outer surface of the input color solid consists of the inner surface of the output color solid and the maximum saturation value of each hue and brightness of the input color solid. Convert so that the entire part surrounded by corresponds continuously, and as a method for the above correspondence,
When the saturation decreases, the hue obtained from any combination of the input color separation image information is the maximum saturation of the six colors blue, green, red, yellow, magenta, and cyan among the colors in the input color solid. When entering a predetermined range before and after any of the hues of a point, it is determined to shift the hue in the direction of the hue of the maximum saturation point in the color of the output side color solid that is the same as the color corresponding to that hue, and Obtain the same value as the converted color system value for any combination of the input color separation image information by using the color system values determined for each combination of the output color separation image information. A color estimation method characterized by determining a combination of output color separation image information. (2) When the three primary colors of the input color separation image information and the three primary colors of the output color separation image information are different, the value of the color system for each combination of the plurality of input color separation image information is calculated, and the Find the value of the above color system for each combination of decomposed image information, and use L^*u^*v^* color system or L^ as the above color system.
Using the *a^*b^* color system, L^* of the values of the color system obtained for any combination of the above input color separation image information is calculated for each combination of the above input color separation image information. The difference between the maximum and minimum brightness values on the achromatic color axis of the input color solid, which is composed of the values of the color system determined for , and the table determined for each combination of the output color separation image information. It is converted according to the ratio of the difference between the maximum value and the minimum value of brightness on the achromatic color axis of the output color solid composed of color system values, and the obtained value is obtained for any combination of the above input color separation image information. Among the color system values u^*, v^* or a^*,
b^* is the hue of the output side color solid whose saturation is above,
If the saturation is smaller than a times the maximum saturation value at lightness (a < 1.0), no conversion is performed, and the saturation is at least a times the maximum saturation value at the hue and lightness of the output color solid at that time. In the case of The outer surface of the input color solid consists of the inner surface of the output color solid and the maximum saturation value of each hue and lightness of the input color solid. As a method of making the above correspondence, when the saturation decreases, the hue obtained from any combination of the above input color separation image information is converted to the above input side color solid. middle 3
When any of the hues at the maximum chroma point of a primary color falls within a predetermined range before and after it, which of the two hues at the maximum chroma point of the three primary colors in the output color solid that are located before and after that on the hue wheel Using the values of the color system obtained for each combination of the plurality of output color separation image information, the above for any combination of the input color separation image information is determined so as to shift the hue in that direction. A color estimation method characterized by determining a combination of the output color separation image information that yields the same value as the value of the converted color system.