The highlight of the hottest color management prep

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The highlight of color management prepress technology

recently, I found that the cover of the same journal was first made in one printing plant and then in another printing plant. As a result, the color was different. Unfortunately, when asked about their operators, he replied: this annoying color inconsistency happens from time to time in the daily process of computer plate making

nowadays, in foreign countries, especially in Europe and America, where the printing industry is quite developed, the technology of computer direct plate making and direct printing has become popular. In the future, with the introduction and application of these technologies in China, the above problems will also become urgent and different from other processing methods, such as:

some plate making centers or printing plants have purchased expensive digital proofing machines for digital proofing, but no matter how the operators adjust parameters, It is difficult for customers to recognize the quality

sometimes, the scanning display effect is very good, but the customer always complains about the poor quality after taking the live, because the color seen on their display changes again

there are also scanned images on the display that are very similar to the color of the original, with good saturation. However, after the mosaic is produced and proofed, the color is different. The warm tone becomes not warm, and the red color turns to pink. Of course, the customer does not accept it

the quality of the scanners used by the plate making departments of some printing plants is not bad. The operators are skilled and experienced, but the images displayed on the display are very different from the originals. Not to mention that the customers who need to scan have comments, but also the operators themselves are confused and dissatisfied

in the final analysis, all these problems belong to color management. There are also some plate making centers, although their hardware is very advanced, but due to the lack of an effective color management system, they can not accurately control all links of color reproduction, and only rely on the so-called experienced masters to judge by experience; However, once experienced masters find new jobs and brain drain, the quality of the whole system can not be guaranteed, resulting in a large amount of equipment investment can not play its due role

in addition, with the continuous development of the printing industry and the introduction of new technologies and processes, some printing plants or special printing starting points become larger, and the companies introduce direct plate making machines or digital direct imaging printing machines. In these systems, traditional proofing is omitted. Digital proofing becomes the key to control the final printing quality. A complete color management system plays an indispensable and decisive role in these new devices

color management has been concerned by the industry since the introduction of color prepress system into China, but color management is a very complex problem after all. In a sense, color management is the management of people's feelings: how much color range can people's eyes see? What is the color range of the original? How to compress the original color to the color range reflected by printing according to different equipment characteristics? None of this is a simple thing. It requires a long time of practice, research and attention to each process of the whole printing process. Data show that many companies have invested energy and time in the project of color management system, but few have achieved real results. Among many prepress image equipment manufacturers, as far as I know, the Heidelberg company's color management system - lino color is relatively successful. As we all know, Heidelberg is the world's most famous printer manufacturer, and Liano Haier is also a world-famous prepress equipment manufacturer. It has accumulated rich experience in color management and prepress product manufacturing. These experiences are based on data. Moreover, Haier has become the prepress Department of Heidelberg. Therefore, the combination of the two provides the printing industry with an overall and perfect solution for pushing the workbench and the upper beam and moving the color horizontally

for color management, the first is the problem of color space, that is, which color space is used for color control. Different devices in the prepress system work in different color spaces. Monitors, digital cameras and scanners work in RGB color space, while printers, proofing machines and printers work in CMYK color space. Since the color space is related to the equipment, the output color of an image on different types of equipment or even the same type of equipment may be different, which is the reason why I mentioned at the beginning of the article that the color of the front and back covers of the same journal is inconsistent

the highlight of Heidelberg's color solution is the use of lab color space in the lino color color management system. This color space is independent of equipment and describes human visual perception in a digital way. Lab color space describes a three-dimensional color space: l represents the change in brightness, a axis represents the change in color from green to red, and b axis represents the change in color from blue to yellow. The color of any point can be expressed in this space. In the lino color color management system, all color conversion and color correction are completed based on the lab space. Because the color range reflected by lab color space is larger than RGB color space and CMYK color space, the conversion of color data from lab space to other color spaces will not cause color deviation due to insufficient data. The scanned image in the lino color color color management system can be stored in the lab format for further correction, and can also be output to the display according to the needs of customers, or called in the group version software after color separation

with a unified color space, the whole printing process cannot be coordinated. Another necessary condition for color management is that you must know the characteristics of each part of your prepress system and master these characteristic data to coordinate the whole printing process. Heidelberg's color management system has a series of tools for measuring the characteristics of scanning equipment, display equipment and output equipment. Including printer, printing proofing machine and printing machine. These characteristic data are stored in the ICC format developed by the international color Committee, and this format is also adopted by most manufacturers today. As long as the application software can support ICC format, it can call these files containing device characteristic data when processing images, so as to achieve the effect of correctly transferring color data

there are several commonly used color measurement tools in the color management system:

● scan open icc

this measurement tool provides the it8 standard manuscripts of Kodak, Agfa and Fuji and the standard data of these manuscripts. These standards are scanned into the computer by the scanner you purchase. The difference between the scanned data and the standard data reflects the characteristics of your scanner, The software automatically generates the ICC file of the scanner for you after calculation. It should be noted that when your scanner changes the lamp tube and CCD, you should re measure its ICC characteristic file

● view open icc

this tool provides a colorimeter and software. The colorimeter is adsorbed on the display, the light measures the color temperature of the display, and then the software automatically generates some color blocks on the screen. The colorimeter measures the color data of the color blocks, and then calculates the ICC file of the display

● print open icc

this measurement tool provides a software, which generates an image containing 210 color blocks in the computer, and then outputs the image on the output device. If it is a printer, directly proofing; If printing proofing machine or printing machine, output film first, and then make plate proofing or printing. Then use a spectrophotometer to measure the color value of each color block on the output image and save it as a file. The computer calculates the ICC characteristic file of the output device based on this file. The computer can also generate a print table of the output device to reflect the characteristics of the output device. Once the characteristics of each product in the prepress system are available, different equipment can be easily calibrated

different models of monitors tend to have different colors, some are blue and some are red. When displaying images, blue and green will be added to the red display, and red and green will be added to the blue display. In this way, the same image will show the same effect on different displays. If some users are not convinced of the effect of the digital proofing machine, they may wish to measure the characteristic curve of the printing proofing machine first, then the color characteristic curve of the digital proofing machine, and then simulate the printing proofing machine with the characteristics of the digital proofing machine with the help of the lino color color color management system. Because the color gamut range of digital proofing machine is generally larger than that of printing proofing machine, good results can be obtained

there is another important problem in the color management system, that is, how to correctly convert color data from one space to another. For example, in the listed lino color color management system, the scanner scans in RGB, but stores in lab. When it is displayed on the display, it should also consider whether the oil is too thin and dirty, and it should be converted from lab color space to RGB color space; When printing or outputting films on the printer, it is necessary to convert from lab color space to CMYK color space. Some operators may have experience in color separation in some software, so they directly convert from RGB to CMYK color space on the display. As a result, the brightness of the image has changed greatly, but it is quite different from the display on the display after printing. Color data conversion in different color spaces is actually a complex algorithm based on a large number of empirical data! Its function is how to convert color data from one color space to another in a certain way, and keep the image hierarchy. In color management, this algorithm is called color match method, which is abbreviated as CMM. The colorsync color management system of apple and the ICM color management system of windows are both introduced or compatible with the color matching method of lino color, which undoubtedly lays a foundation for users to carry out comprehensive color management. Moreover, with the faster and faster operation speed of CPU, the operation results of color matching method will be more accurate in the future

with these functions, the problem of color inconsistency proposed at the beginning of this paper will be solved, so that the color transfer in the printing process can be accurately controlled, and WYSIWYG can be truly realized. The problem of prepress color management that bothers both operators and customers has been solved. It is believed that the development of computer direct plate making and direct printing in China in the future will soon be on the fast track

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