JPH02169272A - Color converter - Google Patents

Abstract

PURPOSE:To contrive higher color reproduction properties at the time of changeover of a paper, an ink or the like by printing a color calibration color scale on a predetermined part of a paper simultaneously with printing on the paper, and correcting the next color printing so as to obtain a density coefficient equivalent to the color scale. CONSTITUTION:At the time of the n-th run of printing, a color scale printed in the (n-1)th run is read by a CCD sensor 16, and the read value is inputted to a color calibrating part 15. The part 15 receives outputs from the sensor 16 and a YMC color scale generating part 17, determines coefficients in a masking equation, and writes the coefficients into a non-volatile memory 14. By such a process, it is possible to determine the coefficients to be used in the next run of printing. Since both an actually outputted signal and a read color signal are clear, the color calibrating part 15 can comform printing to the color scale at the time of determination of the coefficients for color conversion. Thus, the coefficients determined at the n-th run of printing are used at the time of the (n+1)th run of printing. By these operations, high-quality printing can be performed even upon changeover of a paper.

Description

[Detailed Description of the Invention] [(Already required)] This invention relates to a color conversion device for color printing in a color printer, etc., with the purpose of improving color reproducibility when changing paper, ink, etc. , a non-volatile memory for storing coefficients of a masking equation for color conversion, a means for printing a color scale for color calibration at a predetermined location on the paper at the same time as printing on the paper, and a means for printing the next printing after printing the color scale for color calibration. Therefore, a reading means for reading the color scale for color calibration, and an output of the reading means is used to correct the next color printing so that it has a coefficient of density equivalent to the color scale according to the masking equation, and stores it in the nonvolatile memory. and a calibration means.

[Industrial application field]

The present invention relates to a color conversion device for color printing in a color printer or the like.

Color printing has recently been applied to various fields such as color printers and color copies. Typical recording methods for color printers include an inkjet method and a thermal transfer recording method. The former is widely used in the abarre and interior fields because it has high resolution, suppresses gloss, and can produce dark colors. The latter is often used in CAD/CAM, OA equipment, etc.

[Conventional technology]

FIG. 5 is a block diagram of main parts of a conventional color conversion device.

51 is an input signal of three primary colors such as red (R), green (G), blue (8), etc.; 52 is a product-sum circuit; 53 is a memory, which is a ROM that stores coefficients of a quadratic masking equation; 54;
numeral 55 represents output signals of the three primary colors of ink such as yellow (Y), magenta (M), and cyan (C), and numeral 55 represents a printing section. memory 5
The method for determining the content of item 3 is to create several hundred types of color patches, read each color patch with a densitometer, and determine the coefficients of the masking equation by the method of least squares.

The masking equation can be expressed as follows.

In the above equation, the right side aIIna12+--1+aI
J is the content stored in the memory 53, R, G, B
etc. are input signals. Therefore, the product-sum circuit 52 calculates the above masking equation based on the contents of the memory and the input signal, and outputs color signals Y, M, and C.

[Problem to be solved by the invention]

In the conventional method described above, the color reproducibility of color printing is ensured when the ink and paper used when the memory contents were determined are used, but when the ink and paper are insufficient and new ones are replenished. There is a problem that color reproducibility deteriorates. This is due to variations in ink and paper between lofts.

On the other hand, as a countermeasure, it is possible to print color patches of about 200 colors and read them to calibrate the coefficients, but since the masking equation has to be solved every time, the amount of calculation becomes enormous and is not practical.

An object of the present invention is to provide a color conversion device that can improve color reproducibility when switching between paper, ink, and the like.

[Means to solve the problem]

The present invention is a color conversion device for color printing, and includes a non-volatile memo IJ (14) that stores coefficients of a masking equation for color conversion, and a non-volatile memo IJ (14) that is attached to a predetermined location (23) on a sheet of paper (21) at the same time. means (18) for printing a color scale for color calibration; reading means (16) for reading the color scale for next printing after printing the color scale for color calibration; and using the output of the reading means. and a calibration means (15) for correcting the next color printing so that it has a coefficient of density equivalent to the color scale based on the masking equation and storing it in the non-volatile memory.

[For production]

In the present invention, as shown in FIG. 3, the color punch is first used to determine the coefficients of the masking equation, and after printing starts, the colors actually printed are read and fed back to perform color calibration.

In the figure, the vertical axis is the printing density, the horizontal axis is the level, A is the color scale curve at the time of coefficient determination, and B is the color scale curve at the time of printing. Curve B is used to control the actual print quality so that it approaches the print quality using curve A, but since B is sufficiently finely divided, simple linear interpolation is sufficient to match it to 8. When the density level α of point a is required, it is sufficient to output the density level β of point a.

〔Example〕

FIG. 1 is a configuration diagram of an embodiment of the present invention. In the figure,
11 is an input signal such as R, G, B, etc., 12 is a product-sum circuit for color conversion, 13 is an output signal such as Y, M, C, etc., 14
1 is a nonvolatile memory, 15 is a color proofing unit, 16 is a sensor such as a CCD for reading the color after printing, and 17 is a YM
C color scale generation section, 18 is a printing section, and 141 is a backup battery.

FIG. 2 is a diagram for explaining an output image and a color scale for color proofing, and shows an output image 22 printed in color on a paper 21 and a color scale 23 for color proofing for next printing. As shown, immediately after the output image 22 is printed, a color scale 23 for color calibration is printed, and this is used for color calibration for the next printing.

That is, when printing is performed for the nth time, the color scale 23 printed for the (n-1)th time is read by the CCD sensor 16 and this value is input to the color calibration section 15.

Since the color calibration unit 15 knows both the actually output signal and the read color signal, it can adjust the color conversion coefficients to the determined color scale. In this way, the coefficients determined in the nth printing are used during the (n+1)th printing. These operations allow high-quality printing even when the paper is changed.

FIG. 4 is a diagram showing the main parts of the color printer mechanism. In the figure, 41 is an ink sheet, 42 is paper, 43 is a thermal head, 44 is a platen, 45 is a roller, 46 is a light source, and 47 is a sensor.

The color scale 23 printed on the paper is illuminated by a light source 46 and read by a sensor 47. sensor 46
The image is read in step (16) and sent to the color proofing section 15.

The YMC color scale generation section 17 sends its output value to the color calibration section 15. The color calibration section 15 has a sensor 16 and a YM
Upon receiving the output from the C color scale generator 17, the coefficients of the masking equation are determined and written in the nonvolatile memo IJ14. Through such operations, it is possible to determine the coefficients to be used for the next printing.

〔Effect of the invention〕

As explained above, according to the present invention, in color conversion,
Constant color reproducibility is ensured regardless of changes in paper or ink, and therefore printing quality can be improved.

In addition, there is no need to solve the masking equation each time, and simple linear interpolation is sufficient, which greatly simplifies the calculation.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a color conversion device according to an embodiment of the present invention. FIG. 2 is a diagram explaining an output image and color scale for color calibration of the present invention. FIG. 3 is a schematic diagram of color calibration. The figure is a block diagram of main parts of a color printer mechanism, and FIG. 5 is a block diagram of a conventional color conversion device. (Explanation of symbols) 11.51... RGB manual signal, 12, 52... Product-sum circuit, 13, 54... YIJC output signal, 14.53... Non-volatile memory, 15... Color Calibration section, 15, 47... Sensor, 17... YMC color scale generation section, 18, 55.
...Printing section, 21.42... Paper, 22... Output image, 23... Color scale section for color proofing 41... Ink sheet, 43... Thermal head, 44... Platen, 45... Laura.

Claims (1)

[Claims] 1. In a color conversion device for color printing, a non-volatile memory (1
4), and at the same time as printing on the paper (21), the designated area (23) on the paper
means (18) for printing a color scale for color calibration on;
After printing the color scale for color calibration, reading means (1) reads the color scale for color calibration for the next printing.
6), and a calibration means (15) for correcting the next color printing using the output of the reading means so that it has a coefficient of density equivalent to the color scale according to the masking equation, and storing it in the nonvolatile memory. A color conversion device characterized by: