How to realize the standardized process operation

How to realize the standardized process operation of color management (Part 2)

color space management of color conversion

1. Color conversion

color conversion refers to converting the color in the color space on a device to another color space under known conditions according to the one-to-one mapping relationship between different colors in different color spaces. Since the color gamut of the output device is generally smaller than that of the original, scanner and display, the original color gamut must be compressed into the color gamut of the output device. Color management software can convert colors from one space to another gamut space, such as from scanner to display, from display to printer. Color conversion can also simulate the color rendering of another device on one device, such as printing samples on the display

the RGB color space of the scanner is converted to the CMYK color space of the printer, and the RGB color space of the scanner is converted to the RGB color space of the display. The conversion of these color spaces takes the CIE la*b* color space as the reference color space for the conversion process, and the color gamut of various devices can be drawn in the CIE la*b* color space

if the same color is marked as dark green, in the CMYK color space, the area ratio of yellow, magenta, cyan and black spots is, av=47%, am=0%, ac=100%, ak=47%, while in the RGB color space of the display, the red light is 0%, green light is 53%, and blue light is 6%. Color conversion can be done manually or automatically through color management files

2. color space compression and conversion

the completely corresponding mapping relationship between different color spaces does not exist. The color rendering range of the RGB color space of the display is much larger than that of the CMYK color space of the printer. However, further research is needed to confirm which segments need to integrate the mapping relationship, which is also affected by the phosphor characteristics of the display, ambient light and the color rendering characteristics of ink, paper, etc. in the printing process. Therefore, this mapping relationship is based on the premise of minimizing the loss of color information

from RGB color space to CMYK color space, compression conversion is required, and three conversion forms are usually adopted: photo method, field method, and advertising method

photo method, also known as perceptual rendering, is generally used for color conversion of continuous tone photos. It basically maintains the relative relationship between the original color change distribution, so that the brightest part of the image is the dead area (0%), the darkest part is the field (100% points) during printing, and other levels are distributed between these two values in proportion

field method, also known as colorimetric rendering, is the most effective for color patches and can maintain absolute color matching. If the color before color space conversion is in the converted color space, the color remains unchanged; If the color before color space conversion is outside the converted color space, it will be replaced by the closest color, such as the spot color in the map

advertising method is suitable for bright and highly saturated pictures. This color space conversion method is mostly used in commercial advertising production, which can produce pure and saturated colors within the range of printing equipment. The converted colors are not limited to the situation before conversion, and do not pursue color matching between printing equipment, emphasizing a bright and exaggerated publicity effect

Application of color management in prepress system

according to the requirements of color management, developers have launched a variety of different color management schemes. We can choose one of the most practical solutions to apply to our own prepress production

1. Implement

within the scope of application software, establish the transmission specification of color information within a certain utility program and scope, and within the scope of this application software (including hardware), make the input and output devices supported have a unified color space, so as to convert the color coordinates of colors and realize the accurate transmission of colors, and this conversion is independent of the computer operating system. EFI and ficolor (for quaekxpress3.2 and Photoshop6.0 software). Colorsense of Kodak company, lino color of Linotype hell company, which is flatly fixed on the horizontal experimental platform, and fotoflow of AGFA company (used for Photoshop software to effectively protect the safety and legitimate rights and interests of Chinese tourists) can be applied in a certain range

2. Computer operating system

these color management forms can be used as the color transmission standard of computer operating system, and establish a specification for all external equipment manufacturers to make color transmission in a wider range. This implementation scheme has been adopted by Apple's color sync, Adobe's postscript level2, and sun systems' Kodak color management system. At present, apple and adobe are cooperating to develop standards that can support all users

at present, color management has become the key technology of prepress processing. In order to gradually realize the standardization of color management, prepress equipment must have a high degree of stability and repeatability, and all kinds of equipment must have the ability to accurately control the transmission data. With the continuous development of prepress technology and the further improvement and standardization of equipment technical indicators, the standardization of color management will be gradually realized