JPS62208787A - Signal converting method for forming color hard copy from color video signal - Google Patents

Abstract

PURPOSE:To improve a color reproducibility and to make a color matching most optimum by placing a signal converting processing for compensating a color correction masking in the vicinity of the linear color correction masking due to a simple matrix. CONSTITUTION:A look up table (LUT)14 has a function relevant to an analog logarithmic amplifier, by making digital video signals R0, G0, B0 augments, digital three color density data DR, DG, DB corresponding thereto are generated and a gamma correction of a television system is canceled at that time. Then, the color correction masking by the 3X3 matrix of a rear stage is performed in the information of density. Thereby, equivalent neutral density data DR', DB', DB' are formed from a matrix arithmetic circuit 16. Then, the LUC20 is used, analytic density extremely approximate to colorimetric density is obtained according to the coloring characteristic of the color material of an applied recording medium.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a signal conversion method for creating a color hard copy from a color video signal, and in particular to a color correction processing method that improves color reproducibility with simple means. This is what we provide.

(Prior Art) In recent years, systems for converting television images into hard copies have been developed by combining image processing technology and printing technology.

The most problematic issue when creating hard copies from television images is color matching between the television system and the hard copy system. Especially red (R) on TV.
, green (B).

Color reproduction is performed by additive color mixing of the three primary colors of blue (B), whereas in color hard copies, cyan (C), magenta (M
), yellow (Y), and yellow (Y), it is difficult to obtain faithful color reproduction. Also, 3
Color C. The spectral characteristics of the M and Y coloring materials overlap with each other as shown in FIG. 2, and there is a problem in that the color purity decreases when the colors are mixed.

Therefore, a method has been adopted in which signals corresponding to the colors of the original image are chromatically corrected and then supplied to the hard copy system so that the original image and the reproduced image have the same color as a result.

Conventionally, as a means for such color correction or color correction, after color correction masking is applied to the color video signals R0, G0, B0 using a 3×3 matrix as shown below,
There is a method to obtain the amount of dye for color hard copies.

In addition, color video signals R0, G0, B0 are dyed ff1c"
.

After converting into M' and Y', there is a method of applying color correction masking using a 3×3 matrix as described below.

Here, each matrix coefficient a1j is determined by multiple regression analysis so as to faithfully represent the color of the original image.

(Problems to be Solved by the Invention) Masking using a 3×3 matrix as described above is widely used because it is easy to implement with a circuit, but color video signals and pigment amounts are not related to visual characteristics. Since the relationship is not linear, it is impossible to achieve color matching using this alone.

Also, 3×m (m〉3) to correct non-linear distortion
Nonlinear masking has also been proposed using a matrix of .

SUMMARY OF THE INVENTION Therefore, the present invention aims to improve color reproducibility while making use of color correction masking using a 3×3 matrix, and also to provide a signal conversion method that facilitates density management of a hard copy device.

Means for Solving the Problems The method of the present invention for achieving the above objects determines the 19 degrees that a pixel of a hardcopy medium should exhibit in order to create a hardcopy from a color video signal forming a television image. (A) Color video signals R0, G0, B0
Converting into three color densities D R, D C, D B; (
B) Three-color tQ degree D obtained in step (A) above
A 3x3 matrix color correction masking is performed on R, DG, and DB to obtain isoeugenic concentrations DR', DG', and DB.
(C) Isoeugenic IQ degree data D R' obtained by step (B) above.

1) Converting G', DB'' into analytical density data DRo, DGo, DBo corresponding to the coloring characteristics of the hard copy medium.

(Operation) Prior to color correction using a 3x3 matrix, step (A
), the color video signals R0, G0, B0 have three color densities DR,
Converted to DG and DB. Since 73 degrees is closer to the nature of the human eye, which has logarithmic discrimination characteristics for shading, than the luminance of the video signal, color correction masking is performed in the form of 1 degree in the present invention. A look-up table is suitable for implementing this step (A).

The color correction masking of the 3 × 3 matrix in step (B) is a linear masking, which is simple and easy to implement, and isoeugenic under the given conditions DR', DG'
, DB' is obtained.

These isoeugenic densities DR', DG', and DB' correspond to the visual densities, but as they are not compatible with the color hard plastic system, they are analyzed in step CC) corresponding to the coloring characteristics of the hard copy medium. Converted to concentration. This analysis once is approximately equal to the C value measured by a densitometer, and is suitable for use in managing hard copy devices. A lookup table is also suitable for implementing this step (C).

(Embodiment) An embodiment in which the present invention is applied to a color hard copy system using a CRT imaging method will be described with reference to FIG.

In FIG. 1, analog primary color signals R (red) and G (green) are output from a color electronic camera 10.

B (blue) is an analog-digital (A/D) converter 12
are converted into digital signals R0, G0, and B0, respectively, and these digital signals Ro+Go and Bo are input to a look-up table (LUT) 14.

This LUT 14 has a function equivalent to an analog logarithmic amplifier, and outputs a digital video signal RO+G o .

Using Bo as an argument, digital three-color density data DR, DG, and DB are generated, and at this time, the γ correction of the television system is canceled. In this way, in this embodiment, LUT1
4, the video signal is converted to a density close to the visual characteristic (having a logarithmic discrimination characteristic with respect to agricultural consultations), and color correction masking is performed in the subsequent 3×3 matrix in one step. There is.

Three color density data D R obtained from LUT14 in this way
, D C and D B are supplied to a 3×3 matrix calculation circuit 16, where the following matrix calculation is performed.

Here, the matrix coefficient aij is such that the sum of the matrix coefficients of each row is 1 in order to faithfully reproduce one gray point as gray.
be selected to meet the requirements of Therefore, for example, a ll+a 12+a 13=1 is selected. Also, the matrix coefficient a of each diagonal term
ll, a22. The larger a33, the higher the saturation of the corresponding color, for example a ll=2.

a22 knee 1. When a33=-1, the saturation of red is relatively high. Note that 18 is a coefficient setter that provides the matrix coefficient a1j.

Therefore, due to the limitations of the above conditions and linear masking, the matrix calculation circuit 16 outputs isoeugenic concentration data DR',
DG' and DB' are generated.

Therefore, this isoeugenic one-degree data DR', DG'
, DB', even if a hard copy medium or a recording medium is colored, it is not possible to obtain a reproduced image that is coloristically faithful. Therefore, it is necessary to convert the color density into a colorimetrically corresponding density, that is, one degree of colorimetry. However, since the color density cannot be obtained directly by calculation or by a function, in this example, the LU
T20 is used to obtain an analytical density that approximates the embellishing density according to the color development characteristics of the coloring material of a given recording medium. Then, LUT 20 converts the data for concentration conversion according to a theoretical formula based on the spectral characteristics of the coloring material of the recording medium, etc., and analyzes it using the isoeugenic concentration data DR', DG', and DB' as arguments. Concentration data D Ro, D Go+ D
Generate Bo.

Analysis concentration data DR output from LUT20.

D Go and D Bo give the density that a pixel of a recording medium should exhibit.
In order to express a reproduced image on the color photographic paper 30 as a recording medium through the red, green, and blue color lights from 2B, the analytical density data DROI [)Go, DBo are once CR
Voltage ER to be applied to the cathode of T2B.

Convert to E G, E B. LUT2 for this conversion
2 has data defining the correlation between the CRT 26 and the color photographic paper 30. The digital voltage data E R, E G, E B output from the LUT 22 is converted into analog corresponding signals e Rle G, e B by a digital-to-analog (D/A) converter 24, and these signals are converted into C
Red is supplied to the cathode of RT26.

The optical lens 28 emits green and blue light, and as a result, the optical lens 28
The color photographic paper 30 is exposed to light through the light. In addition,
The density management of the hard copy device described above is performed using this LUT2.
All you need to do is make the adjustment in step 2.

The color hard copy image formed in this way is
The color error with the original image is much smaller than before, and the color reproduction is improved.

In the above-described embodiment, a color hard copy is created from the primary color signals R, G, and B obtained from the color electronic camera 10, but a color hard copy can also be created from a received color video signal or a reproduced color video signal in the same manner as described above. Color hard copies can be created. Also, as a printing means, C
In addition to the RT 1mm method, various methods such as the inkgen method and the thermal transfer method can be used.

(Effects of the Invention) As described above, the present invention has the following advantages: By placing signal conversion processing (preferably a lookup table) to compensate for the linear color correction masking using a simple and easy 3×3 matrix before and after the linear color correction masking, The present invention aims at improving color reproducibility or optimizing color matching by a simple means, and also facilitates density management of a hard copy device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to a color hard copy system using a CRT fffl' imaging method, and FIG. 2 shows the three primary colors, cyan (C), magenta (M), yellow ( FIG. 3 is a diagram showing the spectral characteristics of coloring material Y). 10...Color electronic camera, 12...A/
Di conversion n, 14, 20.22... Lookup table (LUT), 1B... 3X3 matrix calculation circuit, 18... Coefficient setter, 26...
・CRT, 30...Color photographic paper.

Claims (2)

[Claims] (1) In a method for determining the densities that pixels of a hard copy medium should exhibit in order to create a hard copy from color video signals forming a television image, (A) color video signals R_0, G_0, B_0 are converted into three color densities; (B) converting the three color densities D obtained in step (A) into D_R, D_G, D_B;
_R, D_G, and D_B are subjected to 3×3 matrix color correction masking to obtain equivalent neutral densities D_R', D_G',
(C) converting the equivalent neutral densities D_R', D_G', D_B' obtained in step (B) into analytical densities D_R_0, D_G_0, D according to the coloring characteristics of the hard copy medium;
_B_0. A signal conversion method comprising the steps of: converting to _B_0. (2) Said step (A) consists of the step of generating three color density data D_R, D_G, D_B by referring to a lookup table having data for density conversion using digital color video signals R_0, G_0, B_0. The step (C) includes generating analytical concentration data D_R_0, D_G_0, D_B_0 by referring to a look-up table having data for concentration conversion using digital equivalent neutral concentration data D_R', D_G', D_B'. A signal conversion method according to claim 1, characterized in that: