JPS60251766A - Color reproducing masking device - Google Patents

Abstract

PURPOSE:To improve the accuracy of color reproduction by correcting a color signal in matching with the saturating characteristic of a spectral optical reflection density characteristic so as to execute masking. CONSTITUTION:Each of color separation signals R, G, B is subject to logarithmic conversion by logarithmic converters 1a-1c and subtractive color mixing digital color decomposition signals C0, M0 and Y0 are obtained. They are impressed to a constant table 2 and a constant subtraction circuit 3. The table 2 sets an inverse matrix for slope and segment of the spectral optical reflection density versus ink quantity curve. The constant subtraction circuit 3 calculates the color signals C1, M1 and Y1 based on the segment set by the table 2 and also calculates (C0-C1), (M0-M1) and (Y0-Y1). A masking circuit 4 obtains the color signal corresponding to the quantity of ink from the result of subtraction and the inverse matrix.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color reproduction masking device that corrects ink proportionality failure and improves color balance with a simple configuration.

[Conventional technology]

In facsimiles, electronic copying machines, etc., a color document is irradiated with light and a lens system is designed to capture the reflected light from the document surface.
), the image is formed on the imaging surface of an image sensor, etc., and the original image signal is obtained by photoelectric conversion. A method is used in which the amounts of the three primary color inks of 0), magenta (M), and yellow (Y) to be used are determined, and these are superimposed and recorded on the paper surface, and colors are reproduced by subtractive color combination.

For example, although an ideal cyan ink should completely absorb only red light and completely reflect blue and green light, it actually absorbs a considerable amount of blue and green light. This also applies to magenta and yellow. Therefore, even through a filter, only the color corresponding to the filter color does not pass through.

In order to faithfully reproduce the color tone of the curry original, it is necessary to perform color correction by masking.

As conventional color reproduction masking methods, for example, a linear masking method and a nonlinear masking method are known.

The linear masking method is based on the assumption that the additive side of printing ink cyan (0° magenta (M) and yellow (Y) and that the proportionality law holds true).
R), green (G), and blue (B) logarithmic values Oor
A masking value of 0 corresponding to the amount of printing ink is obtained by applying a parameter matrix of M 0 1 Y 6 K 3 X 3.
1, M, and Yl are obtained by the following equations.

On the other hand, the nonlinear masking method attempts to compensate for the nonlinearity of ink by performing quadratic and cubic matrix operations on color separation signals.

[Problem that the invention seeks to solve]

However, according to the conventional color reproduction masking method, in the former case, the masking matrix (alj) is a fixed parameter, so even if one chromaticity is the same, input separation signals with different densities are treated differently. Since the chromaticity is output with a certain chromaticity, there is a risk that the balance of one color will be lost. Also, in the latter case.

Since it is necessary to perform matrix calculations many times, the calculations are complicated, and the circuitry required to implement the system is large-scale.

[Means and effects for solving the problems] The present invention has been made in view of the above.

In order to improve color balance with a simple configuration, R,
The G and B color separation signals are converted into digital color separation signals 06 and M.
B HY6, determine the constants of the masking matrix from these, generate a color signal (OB * Mt + Y1)' corresponding to the amount of printing ink using the constants, and subtract it from the digital color separation signal, as well as the result of the subtraction. The present invention also provides a color reproduction masking device that executes masking matrix operation X based on the constants and obtains a color signal corresponding to the amount of ink used for recording.

〔Example〕

Hereinafter, a color reproduction masking device according to the present invention will be explained in detail.

Before giving a detailed explanation of the present invention, a detailed explanation of the present invention will be given.

First, for each cyan, magenta, and yellow ink used for recording, the relationship between the ink amount and the spectral optical reflection density is
Mark it as shown in Figure 1.

Figure 1 shows an example of cyan ink.
For each of 1nC2GinO2BinO, cyan ink was irradiated with light through a red filter, a green filter, and a blue filter, and the reflection density was measured. As shown in FIG. 1, it is possible to consider the spectroscopic optical reflection density by dividing it into a plurality of regions. That is, the spectral optical reflection density TI, T1
By drawing a straight line on each of the curved surfaces divided by the 'i threshold value, the slope and intercept of each concentration region can be determined. for example.

Straight line I FiO' in the inC curve; Oo <
The slope att and the intercept OR for Tt are given, and the straight line 11 gives the slope all and the intercept OR for T1≦O (1<Tt, and the straight line 111 gives the slope all and the intercept OR for Tt<Oo.

Similarly, each of the straight lines iv, v, and vi of the 01nC curve gives a slope azx and an intercept C6, and the Bi,0 curve gives a st and an intercept OB. The same characteristics as shown in Figure 81 were obtained for magenta ink and yellow ink, and the slope aiz l &2m+ass, the intercept MRI M, l MB, and the slope &13°a2!, respectively. +a
3s and the intercepts YR1YIl, , YIl are given.

Color signal corresponding to the amount of printing ink from each section 01゜Ml
, Y, are given by the following equations.

Here, assuming that the approximate values of the amounts of cyan, magenta, and yellow ink that achieve the spectral optical reflection densities of the one-color signals Oo, M, and Yo are ORe Ml *Y, respectively,
The following equation is formed between these.

(The following equation is derived from equation 22.

It is the inverse matrix of 1. aij is (1≦t, J×3).

By performing the matrix calculation of equation (3), a color signal subjected to color reproduction masking can be obtained.

FIG. 2 shows an embodiment of the present invention, in which each of the L, G, and B color separation signals (obtained by photoelectrically scanning a color image) is converted logarithmically, and Oo=R, Mo=1oG % Y o =1
(2) A logarithmic converter Lm that outputs a B digital color separation signal (hereinafter referred to as a color signal).

Based on lb, lc and the output signal Oo of the logarithmic converter 1s, the slope all Hall + all and the intercepts oR, oG
.

OB is obtained, and based on the output signal Me of the logarithmic converter 1b, the slope a1'2 + a1 + aB2 and the intercept MRtMG,
While obtaining MB, the output signal Yo K of the logarithmic converter 1c
Base 5 iteflJ! a 13 1 ass + a
A constant table 2 that outputs each of ss* and intercepts YR9YG and YB, and a color signal Q calculated by equation (1).

Each of Ml and Y is a color signal 00tMO+y.

0(1-01), (Mo-'M1
) + (Yo - Yt ), output No. 41 of the constant subtraction circuit 3 corresponding to the second term on the right side of equation (3), and constant table 2 output (υ).
3) A masking circuit 4 performs masking by executing the matrix operation of equation (3) based on the signal corresponding to (J)-1 in the first term of equation (3).

In the above configuration, each of the color separation signals R, G, and B is logarithmically converted by each of the logarithmic converters 18 to 1e, and the digital color separation signal for subtractive color mixing is obtained as 06 + M6 + Yo
is obtained. These are applied to constant table 2 and constant subtraction circuit 3.

In constant table 2, threshold T and 06+M6. Y6
The slope axt-ass and the intercept 0. ,
O,, OBe MRI M, l M, , YRI
In addition to Y, l YB, (a,
j)-' is set. The constant subtraction circuit 3 calculates the intercept Xk(X((O, M, Y)) set in the constant table 2.

Equation (1) is calculated based on kε(R,G#B)) to calculate each of the color signals ol l Mle yl, and (0001)l(Me Ml)l(Y(1-Ys
) is executed. From the subtraction result of 9 and the (aB)-' signal of constant table 2, matrix operation jI of equation (3)
By executing the f-masking circuit 4, color signals 0!
, M, , Y, can be obtained.

In addition, in the above explanation, the threshold values are T1 and T! However, the number of threshold values can be set arbitrarily.

〔Effect of the invention〕

As explained above, according to the color reproduction masking device of the present invention, since masking is performed by correcting the color signal in accordance with the saturation characteristic of the spectral optical reflection density characteristic, the accuracy of single color reproduction can be greatly improved. Moreover, it can be realized with a configuration that is just an expansion of a linear masking circuit.

[Brief explanation of drawings]

FIG. 1 is a spectral optical reflection density characteristic diagram according to the amount of 77 ink, and FIG. 2 is a block diagram showing an embodiment of the present invention. Description of symbols 1a, 1b, lc...Logarithmic converter, 2...Constant table, 3...Constant subtraction circuit, 4...Masking circuit. Patent applicant Fuji Xerox Co., Ltd. Agent Patent attorney Shin Matsubara 2 Patent attorney Seishunma Muraki Patent attorney Hei 1) Rikai Tadashi Patent attorney Atsushi Ueshima - Patent attorney Hitoshi Suzuki No. 1 Sokyo■

Claims (1)

[Claims] Color images can be obtained by full photoelectric scanning,
and means for outputting digital color separation signals based on the blue color separation signals. constant setting means for determining the color correction coefficient of each additive color mixture component of the digital color separation signal/signal, and setting each constant corresponding to the amount of recording ink of cyan, magenta, and yellow; a constant subtractor for subtracting each of the obtained constants from each of the digital color separation signals; Masking is performed based on the subtraction result output from the constant subtraction section and the inverse matrix of the color correction coefficient by the constant setting means, and color signals corresponding to the respective amounts of cyan, magenta, and yellow ink used for recording are output. A color reproduction masking device characterized by being provided with a masking circuit.