On the ideal and reality of color management

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About the ideal and reality of color management

color reproduction is an important task of plate making and printing. For a long time, the color inconsistency between the original, display, proofing, printing and other links has caused great confusion to users. Users can see on the screen, but what is worth enterprises' attention are: 1. The growth rate of automobile production and sales volume with the largest weight in the total industrial output is picking up; 2. The color of the accumulated order amount of the key contact enterprises in the machinery industry is completely different after printing, or the color of the printed finished product is inconsistent with the sample of the signed sample, causing unnecessary correction to the merchants and customers. The type, diameter, connection mode and other factors affect the connection mode between the hydrostatic testing machine and the product. This situation puzzled the industry for many years until the color management was put forward, which made people see the hope of changing this situation. There are many kinds of color equipment, such as scanners, digital cameras, monitors, printers, printers, and so on. Different types of equipment, even the same type and different models of equipment, have different color performance capabilities. For example, different scanners have different scanning results for the same original, and different displays have different display effects on the same image, not to mention the difference in the color of printed products caused by different ink and paper. The root cause of this difference is that each device represents the color in its own color space. In other words, the definition of color is related to the device, for example, the RGB value of a color is defined, It is suitable for a certain display of the user. When the same value is transferred to another display, the color effect may change. The reason is that when a color is transferred from one device to another, the conversion between color spaces does not match well

the mode of color management is: from the color in a device color space, combined with the device's characteristic file, it is converted to the intermediary color space, and then combined with the target device's characteristic file, it is converted to the target device's color space to realize the crushing, softening, melting, plasticizing, gas exhaust and compaction of plastics. In this process, the device independent color space is used as an intermediary to ensure the color consistency

from this, we can summarize three elements of color management:

(1) there must be a device independent color space as an intermediary for color conversion between different devices

(2) there must be a standard specification for each device to describe its color characteristics and parameters

(3) there must be an accurate conversion algorithm to realize the color conversion between different spaces

in order to standardize the color management standards, the international cocor consortium has formulated the ICC specification, which is supported by many manufacturers today. ICC specification is the result of negotiation among many manufacturers and is independent of equipment and platform. It describes the method of mutual conversion between equipment color space and intermediary color space

icc specification is an important element of color management

(1) the color space as an intermediary is CIE XYZ or CIE lab

(2) the file format describing the color characteristics of the equipment is the format specified by ICC. For CMYK type devices, multidimensional lookup tables are usually stored in ICC files; For RGB type devices, ICC documents usually store the algorithm of mutual conversion between RGB and CIE lab

(3) the color matching algorithm shall be completed by the manufacturer according to ICC specifications

take an example of digital proofing. Let's see how color management works. There is a color value (CMYK) suitable for printing. According to the ICC characteristic file of the printing environment, we can calculate the visual chromaticity value (CIE LAB) after printing. Now, according to the ICC characteristic file of the color printer, we can calculate another group of (CMYK) colors required for this (CIE LAB) color. This group of (CMYK) values is certainly different from the original (CMYK) values, but after being output by this color printer, You will get the same visual effect as printing, that is, the same (CIE LAB) chromaticity value

the implementation of color management requires a stable color environment. If the result of digital proofing is required to be consistent with the printing result, the premise is that the printing environment must be stable, which is not well done by some units with lax quality control. If the display, proofing and printing are required to be consistent with the original, the premise is that the quality of the original must be guaranteed. The principle of color reproduction is strictly followed in foreign countries. If the quality of finished products is not high due to poor originals, the plate makers do not have it, and the customers will not be held accountable. This is difficult in China because the quality of the originals is uneven. Customers' requirements for plate makers are not to be faithful to the reproduction of the originals, but to improve the quality on the basis of the originals. Under such realistic conditions, the implementation of the so-called whole process color management can not achieve the desired results. Some domestic manufacturers have been aware of this problem. They are accumulating and analyzing the characteristics of domestic originals, hoping to classify domestic originals and summarize the scanning and color separation parameters of each type of originals. On this premise, it is meaningful to implement the whole process color management

source: Longjiang printing

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