Discussion on the comprehensive technology of the

Discussion on comprehensive technology of color management II

Step 3: color conversion

color conversion refers to the color conversion between devices or devices and pigments or pigments and pigments. The color range of each device or pigment is different: for example, the color display is RGB color, while the color printing is CMYK color; Moreover, the color range of color displays of different brands (even the same brand) may not be the same; Similarly, the ink color range of different ink manufacturers may also be different

the color conversion in color management is not to provide exactly the same color, but to make the equipment or pigment achieve the most ideal color, and at the same time make the user know the color obtained at the same time. For example, soft proofing uses a color display (RGB color) to simulate the color of four-color printing (CMYK color). In the figure below, the overlapping area of triangles and quadrangles represents the same color of the display and four-color printing, and the colors outside the range are replaced by the closest color

calculated by the color management system (color matching/gamutmapping)

this substitution process is not random and disordered. The international color association has proposed four solutions:

(1) absolute chromaticity method. This method keeps the colors in the same color range unchanged, and replaces the colors beyond the color range with boundary colors. When the input color range is close to the output color range, this method can obtain ideal color reproduction

(2) relative chromaticity method this method changes the white point calibration, and all colors will be changed accordingly according to the change of the calibration point, because all the colors in the super excellent spatial range are also replaced by the colors with the closest boundary. This method can calibrate the white dots according to the color of printing paper at high speed, and is suitable for color space conversion with close color range

(3) highlight saturation method this method pursues high saturation and nonlinear compression of saturation, which may be unfaithful to the original. Its purpose is to get saturated color under the condition of equipment limitation

(4) sensory this method not only maps the gamut, but also optimizes the gradient. It maintains the relative relationship of colors, that is, adjust the conversion ratio according to the color rendering range of the output device, so as to achieve the consistency of colors in the sense

5. Common color management systems

there are many products of color management at present, but they can be generally divided into several levels: the first is color management in computer operating system (such as ICM in windows, colorsync in MAC, etc.), and the second is color management software installed in operating system (such as kpcms of Kodak, colortune of Agfa, Photoshop of adobe, etc.), There are also color measurement instruments (such as colorelite of aseli, spectrolino of Grenada, etc.) and color management hardware (such as macctu color transfer interface card of lianoherr)

(1) colorsync

the colorsync color management system of MAC is a color management system released by apple. It adopts ICC Standard and takes Lab color space as the standard reference space. It is a system level color management software applied under the Mac operating system. It is an open color management system. Users can convert colors between different color management systems through the plug in module of colorsync

colorsync system consists of three parts, an ICC Standard color description file, color matching method (CMM) and application software interface (API). The device description file defines the color characteristic information of the device, through which the color range that the device can display, capture and reproduce can be obtained. When using colorsync to create a file, a profil composite polyurethane adhesive industry sales revenue of 15.65 billion yuan and 19.37 billion yuan e file will be stored in the file. In this way, when processing images with colorsync description files on other devices, colorsync

will perform color space matching operations by comparing the characteristics of the device that creates the image with the characteristics of the display, so as to obtain the best color effect. Color matching method is the core part of colorsync, which realizes the conversion of different color spaces. More importantly, colorsync's color conversion mode adopts the high-quality color matching technology of Linotype hell, so users can use a better color gamut compression method to deal with colors outside the color gamut

due to the different expressive power of various application software on color, the same image color will have different appearance from image scanning to final replication. In order to master accurate colors at all times in work, it is necessary to carry out effective color matching of these application software. Color matching can be carried out through the application software of colorsync, so as to achieve the same purpose

(2) Photoshop

Adobe's Photoshop color management system, as the most famous image processing software of adobe, has its irreplaceable position in image processing. The color management feature of Photoshop software is controlled by monitor setup, printing inks setup and color separation settings

in order to make the color seen by the user on the screen as close as possible to the color of the output sample, the user's system must be corrected first. The time-consuming and money-consuming accurate color workflow must start from the display correction and display setting. "Monitor Setup" includes two parts: display calibration and display setup. In the display, the correct selection is made according to the display type, phosphor powder, color temperature, etc., so that when the image is converted into color mode, the correct color conversion can be carried out according to the settings of the above parameters

the basic purpose of printing ink setting is that Photoshop provides information about the ink, paper and printing machinery used for final printing. Different paper has different absorption and dot enlargement of ink, different ink has different color rendering, and different printing methods have different dot enlargement rates. Therefore, these parameters need to be set in "printing inks setup". After obtaining the basic information from the RGB image data and the display data obtained in the "Monitor Setup", the color mode conversion can be completed according to the characteristics of the final printing conditions

the most important item in color separation is the determination of the amount of black plate. Theoretically, color separation from one RGB value can produce multiple CMYK values, and the final printing effect should be the same. However, due to the ink receiving capacity of different printing papers and the characteristics of different printing machines, it may not be possible in theory. Therefore, it is necessary to set the type of color separation, the amount of black plates, and the percentage of total printing points accordingly

(3) kpcms

Kodak's color management system kpcms supports both PC and MAC platforms. Unlike colorsync and Photoshop, kpcms tends to use a modular approach to color management, and provides several local modules, which can be combined to form a complete color management system. And it has the function of color management for the process of photo

CD image input. Kodak color management system generally includes kpcms, DCP, PICC and PCS100 modules, which can be used separately or combined into a complete color management system

kpcms module (Kodak precision color management system) provides enough device description files in accordance with ICC Standard format. Its input devices include RGB image sources and CMYK image sources, and its output devices include printers and proofing machines. However, it has great limitations because it cannot describe the device itself

dcp module (device color description file startup software package) is a software package designed to provide display and output color correction for photocd images. When opening photocd images, users are required to select two device description files. The input device description file is a description file of a photo CD device, and the output device description file can be a display description file. Note: the experimental experience description file, It can also be a color proofing machine description file

picc module (precise input color characterization) provides a scanner practical standard program to enhance the function of DCP

(4) colortune

colortune of AGFA is a software solution for professional color management. Unlike the color characteristic files of scanners, display screens or printers that use general color management built into the operating system, colortune uses personalized ICC color characteristic files to improve the quality of your color workflow. Colortune helps you establish the color characteristics of the scanner and display screen, and the upgraded colortune Pro allows you to establish the color characteristics of your own output device or printer

colortune can ensure consistent color output under different devices, such as scanners, display screens or printers. Although we know that everyone feels different about color, in fact, the ability of each device to process and reproduce color is also different. Using colortune, Agfa's professional color image processing technology allows you to give full play to the color processing capabilities of all devices

Agfa's colortune can not only ensure accurate color, but also has high reliability and high predictability. Once you use colortune to adjust your output device, you can reliably copy the colors you want, and even predict the image effect on the printer or any other way according to the image on the screen, such as four-color printing, high fax color printing, etc. Colortune keeps everything under your control

(5) colorelite

aseli's colorelite system is a well-known high-precision innovative portable solution that enables creative professionals to manage the color of all devices, including monitors, scanners, digital cameras and printers. Pulse colorelite system includes a new handheld precision spectrophotometer, an award-winning display calibrator, advanced color management software and multi-function Pathfinder TM handheld scanning guide

(6) CPS

Heidelberg's CPS color management software was developed by the world-famous prepress equipment development and manufacturer Linotype hell, which was acquired by Heidelberg in 1997. CPS color management software includes linocoloe, viewopen ICC, scanopen ICC and printopen ICC. The first is the color management center and scanner driver software, and the latter three are the feature software for manufacturing screens, input and output devices respectively. (to be continued)