JPH07276711A - Color-correcting circuit - Google Patents

Abstract

PURPOSE:To provide a color-correcting circuit capable of obtaining the reproducibility of a color near a color of an input image having various states. CONSTITUTION:A color-correcting circuit 13 has a color-correcting look up table 14 corresponding to an R color signal, a color-correcting look up table 15 corresponding to a G color signal, a color-correcting look up table 16 corresponding to a B color signal, and a selecting circuit 18 which selects a specific table from respective color-correcting look up tables 14, 15, 16 on the basis of selecting operation with an external switch. Each color-correcting look up table 14, 15, 16 consists of a ROM, and the ROM contains an output color data corresponding to an inputted color signal and besides, a plurality of tables wherein their correcting values are stated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color correction circuit used in a color image hard copy device or the like.

[0002]

2. Description of the Related Art Generally, as a color image hard copy apparatus, the color of an input image is corrected by referring to a color correction look-up table, and a color image is formed on a photographic paper by the corrected color. There is something.

Next, the above-mentioned color image hard copy apparatus will be described with reference to the drawings. FIG. 3 is a block diagram showing a main part of a conventional color image hard copy apparatus.

As shown in FIG. 3, the color image hard copy apparatus includes a memory circuit 2 for storing the R, G, B color signals forming the input image data 1. Memory circuit 2
Is a color correction circuit 3 for each of the stored R, G, B color signals.
Output to.

The color correction circuit 3 includes a color correction lookup table 4 corresponding to the R color signal, a color correction lookup table 5 corresponding to the G color signal, and a color correction lookup table 6 corresponding to the B color signal. Have. Each color correction lookup table 4, 5 and 6 comprises a ROM
In M, the correction value is described together with the output color data corresponding to the input color signal.

The R, G, and B color signals output from the memory circuit 2 correspond to the corresponding color correction look-up table 4.
Given to 5,6. For example, the R signal from the memory circuit 2 is given to the color correction lookup table 4,
The output data stored at the address corresponding to the data indicated by the signal is read. The output data is data for correcting the red color data indicated by the R signal and converting the corrected red color data into cyan color data.

Similarly, the G signal from the memory circuit 2 is applied to the color correction lookup table 5, and the output data stored at the address corresponding to the data indicated by the G signal is read out. This output data is data for correcting the green data indicated by the G signal and converting the corrected green data into magenta color data. The B signal from the memory circuit 2 is given to the color correction lookup table 6, and the output data stored in the address corresponding to the data indicated by the B signal is read. This output data corrects the blue data indicated by the B signal,
Further, it is data for converting the corrected blue color data into yellow color data.

Color correction lookup tables 4, 5, 6
The output data read from is supplied to the printed circuit 7. The print circuit 7 transfers the color of each ink sheet to the printing paper based on each output data, and forms the output image 8 corresponding to the input image on the printing paper.

Each color correction lookup table is created on the basis of the specifications of the image hard copy device, the specifications of the ink sheet used in this device, the specifications of the printing paper, and the like.

Next, a method of creating this color correction lookup table will be described.

First, a plurality of sets of color chart samples whose chromaticity values are predetermined, ink sheets whose specifications are predetermined, and printing paper whose specifications are predetermined are prepared.

Then, the color image hard copy apparatus performs copying on the color chart sample without performing color correction to obtain a printing paper on which the color of the color chart sample is transferred.

After copying the color chart sample, the chromaticity of the color transferred to the photographic paper is measured and the measurement result is output. The result of chromaticity measurement is compared with the chromaticity of the color chart sample to be copied, and the chromaticity difference is calculated from the result of this comparison.

Next, the input / output characteristics of the color image hard copy device are estimated from the calculated chromaticity difference, and the input / output characteristics are modeled. From this modeled input / output characteristic, the degree of color correction is determined so that the color transferred to the photographic paper is almost the same as the input color, and the degree of color correction is digitized.

After digitizing the degree of color correction, a color correction look-up table describing the numerical value indicating the degree of color correction is created.

However, although this color correction lookup table creating method can improve the reproducibility of the color transferred to the photographic paper for the color near the chromaticity of the color chart sample, the color of the color chart sample can be improved. The color reproducibility with respect to colors far from the vicinity is reduced. That is, the characteristics of the color correction lookup table are determined by the selected color chart sample.

Therefore, since a set of color correction look-up tables is used in the color image hard copy apparatus, for example, the reproducibility of green and blue seen in landscape images and the reproducibility of skin colors seen in portrait images. , Contrast, also
A set of color correction lookups when individual color reproducibility for each aspect of the input image is required, such as high-brightness color reproducibility found in computer graphics (hereinafter referred to as CG) images. It is very difficult to perform faithful color reproduction on the input image having each aspect in the table.

[0018]

As described above, in the conventional color correction circuit, since there is one set of color correction look-up tables, one set of color correction look-up tables can be applied to an input image having various aspects. , It is very difficult to perform faithful color reproduction.

An object of the present invention is to provide a color correction circuit capable of obtaining color reproducibility close to the color of an input image having each aspect.

[0020]

SUMMARY OF THE INVENTION The present invention is a color correction circuit used in a color image hard copy device for copying an input image onto a transfer material such as photographic paper, and for each color data forming the input image. A plurality of color correction look-ups each having a plurality of tables, each of which is provided on the transfer material and describes output color data for forming an output image corresponding to the input image and correction values for each color data of the input image. A table and a selection circuit for selecting an optimum table from the color correction lookup tables for each color data according to the mode of the input image are provided.

[0021]

[Operation] In the color correction circuit of the present invention, a color correction lookup table is provided for each color forming the input image, and an output image corresponding to the input image is output to the transfer material for each color correction lookup table. A table in which output color data for forming and correction values for each color data of the input image are described is provided so as to be selectable.

Since a predetermined table is selected from the color correction look-up tables for each color according to the mode of the input image, it is possible to obtain color reproducibility close to that color for the input image having each mode. it can.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the main part of a color image hard copy apparatus in which an embodiment of the color correction circuit of the present invention is used.

As shown in FIG. 1, the color image hard copy apparatus includes a memory circuit 12 for storing the R, G, and B color signals forming the input image data 11. The memory circuit 12 outputs the stored R, G, and B color signals to the color correction circuit 13.

The color correction circuit 13 includes a plurality of tables Tn.
(N = 1, 2, 3, ...) And a color correction lookup table 14 corresponding to the R color signal and a plurality of tables Tn.
(N = 1, 2, 3, ...) And a color correction lookup table 15 corresponding to the G color signal and a plurality of tables Tn.
(N = 1, 2, 3, ...), each color correction look-up table 14 corresponding to the B color signal, and each color correction look-up table 14, based on the selection operation of the external switch 17.
A selection circuit (selection circuit) 18 for selecting a predetermined table from the tables Tn of 15 and 16. Each of the color correction lookup tables 14, 15 and 16 is composed of a ROM, and the ROM includes a plurality of tables Tn for describing the correction values together with output color data corresponding to the input color signal.

R, G, B output from the memory circuit 12
Each color signal of the corresponding color correction lookup table 1
It is given to 4, 15, and 16. For example, the memory circuit 12
Is applied to the selected table T1 in the color correction lookup table 14, and the output data stored in the address corresponding to the data indicated by this R signal is read out. The output data is data for correcting the red color data indicated by the R signal and converting the corrected red color data into cyan color data.

Similarly, the G signal from the memory circuit 12 is applied to the selected table T1 in the color correction lookup table 15, and the output data stored at the address corresponding to the data indicated by the R signal is output. Read out.
This output data is data for correcting the green data indicated by the G signal and converting the corrected green data into magenta color data. The B signal from the memory circuit 12 is applied to the selected table T1 in the color correction lookup table 16, and the output data stored at the address corresponding to the data indicated by the B signal is read out. This output data is data for correcting the blue color data indicated by the B signal and converting the corrected blue color data into yellow color data.

Each color correction lookup table 14, 1
The output data read from 5, 16 is printed circuit 19
Given to. The print circuit 19 transfers the color of each ink sheet to the printing paper based on each output data, and forms an output image corresponding to the input image on the printing paper.

Next, the operation of the color image hard copy device will be described.

First, the user determines the table to be selected by looking at the mode of the input image, and operates the external switch 17 to select this table. When the external switch 17 is operated, the signal indicating the mode of the input image is selected
Given to 8. The select circuit 18 receives the color correction lookup tables 14 and 1 on the basis of the signals input thereto.
A corresponding table is selected from among 5 and 16.

Next, the input image data is taken into the memory circuit 12 as R, G, B color signals. The R, G, B color signals fetched in the memory circuit 12 are applied to the selected table Tn in the corresponding color correction lookup tables 14, 15, 16.

For example, when the reproducibility of green and blue seen in a landscape image is particularly required, the reproducibility of skin color seen in a human image, the contrast, and the computer graphics (hereinafter referred to as CG) image are seen. An R signal which requires color reproducibility for each aspect of the input image, such as high-luminance color reproducibility, is given to the table T1 of the color correction lookup table 14. The data indicated by the R signal is taken into the table T1 as an address, and the output data written at this address is read. The output data is data for correcting the red color data indicated by the R signal and converting the corrected red color data into cyan color data.

Similarly, the G signal is applied to the table T1 of the color correction lookup table 15. The data indicated by the G signal is taken into the table T1 as an address, and the output data written at this address is read. The B signal is applied to the table T1 of the color correction lookup table 16. The data indicated by the B signal is taken into the table T1 as an address, and the output data written at this address is read.

Each color correction lookup table 14, 1
Output data from 5 and 16 are applied to the printed circuit 19. The printed circuit 19 selects an ink sheet based on the output data from the color correction look-up tables 14, 15, 16. The ink of the selected ink sheet is transferred to the printing paper, and a color image corresponding to the input image is formed on the printing paper.

Similarly, each aspect of the input image, such as the reproducibility of skin color seen in a human image, the contrast, and the reproducibility of high-intensity color seen in a computer graphics (hereinafter referred to as CG) image, etc. When the color reproducibility for each of the input images is individually required, a color reproduction close to the color of the input image can be obtained by selecting an appropriate table for each color correction lookup table for each input image mode.

As described above, the optimum table is selected from the color correction lookup tables 14, 15 and 16 according to the mode of the input image, so that the color of the color image formed on the photographic paper is the same as that of the input image. It becomes very close to the color, and the color reproducibility of the output image with respect to the input image can be made very high.

Next, another color correction circuit will be described with reference to the drawings. FIG. 2 is a block diagram showing the main part of a color image hard copy apparatus in which another embodiment of the color correction circuit of the present invention is used.

As shown in FIG. 2, the color image hard copy apparatus includes a memory circuit 12 for storing the R, G, and B color signals forming the input image data 11. The memory circuit 12 outputs the stored R, G, and B color signals to the color correction circuit 21.

The color correction circuit 21 includes a plurality of tables Tn.
(N = 1, 2, 3, ...) And a color correction lookup table 14 corresponding to the R color signal and a plurality of tables Tn.
(N = 1, 2, 3, ...) And a color correction lookup table 15 corresponding to the G color signal and a plurality of tables Tn.
(N = 1, 2, 3, ...), and a feature for the aspect of the input image is extracted from each color signal from the color correction lookup table 16 corresponding to the B color signal and the memory circuit 12,
A feature extraction circuit 22 for generating a signal indicating a table to be selected among the color correction lookup tables 14, 15, 16 based on the extracted features, and the feature extraction circuit 22.
Color correction lookup table 1 based on signals from
It has a select circuit 18 for selecting a predetermined table from the tables Tn of 4, 15, and 16.

Each color correction lookup table 14, 1
Reference numerals 5 and 16 are ROMs, and the ROMs include output color data corresponding to the input color signals and a plurality of tables Tn for describing the correction values.

R, G, B output from the memory circuit 12
Each color signal of the corresponding color correction lookup table 1
It is given to the table selected by the select circuit 18 among 4, 15, 16. Each table Tn has output data stored at the address indicated by the corresponding color signal, this output data corrects the color data indicated by the corresponding color signal, and the corrected color data is converted into a predetermined output color. It is data for converting into data.

Each color correction lookup table 14, 1
Each of the output data read from 5, 16 is applied to the printed circuit 19. The print circuit 19 transfers the color of each ink sheet to the printing paper based on each output data, and forms an output image corresponding to the input image on the printing paper.

Next, the operation of the color image hard copy device will be described.

First, the input image data is taken into the memory circuit 12 as R, G, B color signals. The R, G, and B color signals captured in the memory circuit 12 are provided to the feature extraction circuit 22. The feature extraction circuit 22 is the memory circuit 1
A feature for the aspect of the input image is extracted from each color signal from No. 2 and a signal indicating a table to be selected among the color correction lookup tables 14, 15, 16 is generated based on the extracted feature.

The signal from the feature extracting circuit 22 is given to the select circuit 18, and the select circuit 18 receives the feature extracting circuit 2.
The table Tn in the color correction look-up tables 14, 15, 16 corresponding to each color signal is selected based on the signal from 2.

A selected table Tn among the color correction lookup tables 14, 15, 16 corresponding to each color signal.
The R, G, and B color signals from the memory circuit 12 are fetched into.

For example, the R signal is applied to the table T1 of the color correction lookup table 14. The data indicated by the R signal is taken into the table T1 as an address, and the output data written at this address is read. The output data is data for correcting the red color data indicated by the R signal and converting the corrected red color data into cyan color data.

Similarly, the G signal is applied to the table T1 of the color correction lookup table 15. The data indicated by the G signal is taken into the table T1 as an address, and the output data written at this address is read. The B signal is applied to the table T1 of the color correction lookup table 16. The data indicated by the B signal is taken into the table T1 as an address, and the output data written at this address is read.

Color correction lookup tables 14, 1
Output data from 5 and 16 are applied to the printed circuit 19. The printed circuit 19 selects an ink sheet based on the output data from the color correction look-up tables 14, 15, 16. The ink of the selected ink sheet is transferred to the printing paper, and a color image corresponding to the input image is formed on the printing paper.

As described above, the feature extraction circuit 22 automatically selects the optimum table from the color correction look-up tables 14, 15, 16 according to the feature indicated by the mode of the input image. You can save time. Further, the color of the color image formed on the printing paper becomes very close to the color of the input image, and the color reproducibility of the output image with respect to the input image can be made very high.

[0052]

As described above, according to the color correction circuit of the present invention, it is possible to obtain the color reproducibility close to the image color of the input image having each aspect.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of a color image hard copy apparatus in which an embodiment of a color correction circuit of the present invention is used.

FIG. 2 is a block diagram showing a main part of a color image hard copy apparatus in which another embodiment of the color correction circuit of the present invention is used.

FIG. 3 is a block diagram showing a main part of a conventional color image hard copy device.

[Explanation of symbols]

 13, 21 Color correction circuit 14, 15, 16 Color correction lookup table 17 External switch 18 Select circuit (selection circuit) 22 Feature extraction circuit Tn (n = 1, 2, 3, ...) Table

Claims (2)

[Claims] 1. A color correction circuit used in a color image hard copy device for copying an input image onto a transfer material such as photographic paper, the color correction circuit being provided for each color data forming the input image and inputting to the transfer material. A plurality of color correction lookup tables having a plurality of tables in which output color data for forming an output image corresponding to the image and correction values for each color data of the input image are described; And a selection circuit for selecting an optimum table from the color correction lookup tables for each color data. 2. A feature extraction circuit for extracting a feature indicating a mode of the input image and for instructing a selection table to the selection circuit based on the extracted feature. The described color correction circuit.