Digital gray balance control law of printing quality

Abstract The improvement of printing quality requires the establishment of a data-oriented concept so that the stability of the reproduction can be controlled. Gray balance measurement is often used to determine whether the replica is an important basis for color cast, so the gray balance of data will be able to improve the quality and stability of print. The data-based gray balance control law is the subject of this study.

Preface

Gray balance is an important basis for judging copying when making color copies. After the color reproduction is measured by a concentration meter, the ink amounts of the three primary colors are overprinted to achieve neutral gray. Neutral gray produces a color cast that is easily noticeable because people are particularly sensitive to gray. When the original is reproduced, his neutral color is the same as the neutral color of the replica, then the hue balance of the color reproduction can be considered correct. Therefore, the color copying staff regards the gray portion as the basis for the color cast and the reference for printing quality.

Since the yellow, magenta, and cyan inks contain noises other than themselves, they cannot be overprinted with the same concentration to get the concentration you want. Therefore, in order to make the prints not be color cast, it is necessary to find the appropriate concentration of the three primary colors of the overprint to achieve the gray balance. In the process of color reproduction, the main control of gray balance is to control the area size of the dots of the three primary colors, rather than the thickness of the ink. The grey color printed by the three primary colors of different sizes is used to determine whether or not the grey color is balanced. The concentration is measured in gray color patches. When the values ​​of clear, magenta, and yellow are the same, the gray balance has been reached.

Because there are many different inks in a printing plant, the dot sizes of the three primary colors combined by different inks may be different, not to mention the errors in different environments or different requirements and conditions. The factors that affect the gray balance include ink volume, paper, dot area,,,,,, and so on, and the balance value needs to be applied to the CIE uniform color space and the color difference formula. Therefore, this paper hopes to sort out some methods for obtaining gray equilibrium concentration values, describe these methods in detail, compare the advantages and disadvantages of these methods, and the applicable environment, and then obtain the rules of the gray balance control method.


è´°, theoretical basis

The theoretical basis is mainly to facilitate readers to understand the text, so it is divided into two points, one is noun explanation second, CIE uniform color space and color difference formula

I. Glossary

(A). Gray Balance (Gray Balance)

After the color reproduction is measured by a concentration meter, the ink amounts of the three primary colors are overprinted to achieve neutral gray. In general printing will add a black version to increase the dark part of the hierarchy.
(B). Chroma

The color has a neutral color component, the higher the value, the farther away from the neutral color; the lower the value, the closer to the neutral color.

(C). Colorimetry

It is a comprehensive science that involves the cross-disciplinary fields of physical optics, visual physiology, visual psychology, psychophysics, etc., based on the science of human visual perception to measure color.

(d). CIE Color System (CIE International Commission on Illumination International Commission`
Eclairage)

The stimuli of color and the sense of color are the source, the attenuator, and the detector. These three elements form the basic structure of the CIE color system.

(e). CIE Standard Illuminants

Defined from the standpoint of spectral energy distribution, it may not be able to be made into a physical light source for human visual and color measurement.

(VI). CIE Standard Light Sources

The CIE standard illuminant was calibrated by a body made of CIE Standard Illuminator to simulate its relative spectral energy.

Second, CIE uniform color space and color difference formula:

(a). CIELAB color space:

CIE used the 1976 L*a*b* color space, abbreviated as CIELAB.
a*: Red and green coordinates, with red at timing and green at negative.
b*: stands for yellow and blue coordinates, yellow for timing, and blue for negative.
L*: the brightness value, 0 is the ideal black, and 10 is the ideal white.

(b).CIELUV color space:

CIE recommends the second uniform color space, "CIE 1976 L*u*v* color space" referred to as CIELUV. u*: Red and green coordinates, with red at timing and green at negative.
v*: yellow-blue coordinates, yellow on timing, and blue on negative.
L*: lightness.

(c).CIELCH color space

Other representations from CIELAB and CIELUV are called CIELCH (L* C* h°)
C *: chroma as h °: hue angle, representative hue

(D). CIELAB color difference formula:

(e). CIELUV color difference formula:

(to be continued)