How to implement the standardization flow operation of color management (below)

Color space management for color conversion

1. Color conversion

    The color conversion refers to a one-to-one mapping relationship between different color spaces according to different colors, and the color in a color space on a device is converted into a color space in another known condition. Since the color gamut of the output device is generally smaller than that of the original document, the scanner, and the 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, such as from a scanner to a monitor, and from a monitor to a printer. Color conversion can also simulate the color rendering of another device on a device, such as simulating a printed proof on a display.

The CMYK color space converted from the RGB color space of the scanner to the printer is converted from the RGB color space of the scanner to the RGB color space of the display. The conversion of these color spaces uses the CIE La*b* color space as the reference color of the conversion process. Space, color rendering fields of various devices can be drawn in CIE La*b* color space.

If a color is marked as dark green, in the CMYK color space, the dot area ratios of yellow, magenta, cyan, and black dots are: av=47%, am=0%, ac=100%, ak=47%, and the display In the RGB color space, red light is 0%, green light is 53%, and blue light is 6%. Color conversion can be corrected manually by hand or automatically through color management files.

2. Color space compression conversion

There is no corresponding mapping relationship between different color spaces. The color rendering range of the display RGB color space is much larger than the color rendering range of the printer CMYK color space, and this mapping relationship is also affected by the display screen phosphor characteristics and environment. Effects of coloration characteristics of ink, paper, etc. in light and printing processes. Therefore, this mapping relationship is based on the premise that the loss of color information is minimal.

From the RGB color space to the CMYK color space for compression conversion, usually three kinds of conversion formats are used: photo method, field method, and advertisement method.

The photographic method is also called Perceptual Rendering. It is generally used for the color conversion of continuous photographs. It basically maintains the relative relationship of the original color change distribution, making the brightest part of the image a non-printing area (0% ), The darkest place is printed on the spot (100% dot), and the other levels are distributed proportionally between these two values.

The field method, also known as Colorimetric Rendering, is the most effective for color patches and can maintain absolute color matching. If the color before the color space conversion is in the converted color space, the color remains unchanged; if the color space before the color space conversion is outside the converted color space, the nearest color is replaced, such as the map in the Color and so on.

Advertising law, suitable for bright and saturated images, this color space conversion method is mostly used for commercial advertising production, can produce pure and saturated colors in the printing equipment range, the converted color is not rigidly adhered to before the conversion The pursuit of color matching between printing equipments is not emphasized, and a clear and exaggerated publicity effect is emphasized.

Application of color management in prepress system

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

1. Implemented within the application software

A transfer specification of color information is established in a certain utility program and scope, and within this application software (including hardware), a uniform color space is provided between the input and output devices supported thereby to convert the color coordinates of the color. Achieve accurate color transfer, and this conversion has nothing to do with the computer operating system. EFI and Ficolor (for Quaek XPress 3.2 and Photoshop 6.0 software). Colorsense from Kodak, Lino Color from Linotype-Hell, and FotoFlow from Agfa (for Photoshop software) can be applied within a certain range.

2. Computer operating system

These color management forms can be used as the color transfer standard for computer operating systems, establishing a specification for all external device manufacturers, allowing color transfer to be carried out in a wider range. Color Sync from Apple Inc., Postscript level 2 from Adobe, and the Kodak color management system used by Sun Microsystems have been used for this type of implementation. Currently Apple and Adobe are working together to develop standards that support all users.

At present, color management has become a key technology for prepress processing. To gradually realize the standardization of color management, prepress equipment must be highly stable and highly repeatable. Various devices must have accurate control over transmission data. Ability. 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.