Three forums: printing digital color management is more perfect
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First, the printing industry color reproduction requirements are high
Printing is a graphic communication industry. In the image and graphics section, it has now become colorized. Even newspapers have a large amount of color, so image reproducibility and color reproducibility play an important role in quality. Coupled with a lot of merchandise packaging, its image, the color of the dots to form a color, is the basis for many customers to distinguish between authenticity. Today's printing and peripheral industries are increasingly divided, and regardless of hardware and software driven by electronic digital technology, more accurate measurement, simulation, and control. Therefore, print users have stricter requirements on the difference in color reproduction of printed products, and some are more demanding. They not only exceed the ability of visual recognition, but also use instruments to measure dark parts and dark parts. The eye is already insensitive to the error value, making it beyond the necessary measurement requirements, and losing the scope of the visual product requirements.
Second, color management from closed to open
In the 1970s and 1980s, when installing an electronic scanning color separation machine, the technician would request to output a test color mesh, do printing and printing proofing, and establish a closed color reproduction color gamut and color balance system of the printing factory. If there are different printing papers, It also divides the glossy copper plate, the matte copper plate, and the non-coated three curves for color reproduction management. The author asked him what if the plate-making factory responded to many different printing factories? He also couldn't do it one by one, only to achieve the color management system of the proofing machine.
Today, we no longer rely on R, G, B tri-color filter concentration values for color management, because it can not do the calculation of color difference values, and most of them use Lab stereo gamut space, L color brightness value and ab and - The hue plane position of ab, when it is the data of color value, the color data of Lab can be used regardless of the change value of RGB to CMYK, RGB to different RGB performance, CMYK to RGB, CMYK to different CMYK output performance. To calculate the conversion. Moreover, the two color gaps can also be used to display the color difference of the plane or the three-dimensional gap with the value of △E, so the open prepress and printing equipment using this color gamut space becomes the mainstream of color management, in different brand equipment, Under the combination of different hardware, software color materials and media materials, the color value display and difference adjustment are performed. Today, the ISO 12647 system also uses the Lab data value to do the color specification and operation of the main body, so that the color reproduction can be more open and consistent performance.
Third, image input, shielding display and various output management
The traditional image input center has been equipped with a professional roller or platform CCD scanner, with good IT8 7-1 7-2 for transmissive and reflective color correction to capture image files. But today it has become a general amateur CCD camera, even the image files captured by the mobile phone camera, reproduced under different hardware CCD and software conversion and color mechanism, plus the environmental lighting color temperature changes, today, many prepress work has no funds And time, to do the artificial common sense color, the adjustment of the tone of the work, so today many prints are not taken by the studio, there are color managers, many are the image of the tone and the color difference is very large, in the future use a small variety When printing without a plate, it is more serious because the situation is worse, so the image processing software of AI artificial intelligence has its necessity.
Regarding the color reproduction of the screen, it is more important now to promote soft proofing of the remote screen and soft proofing of the paperless printing. Some advanced screens have automatic color correction equipment and programs, or color management software, and use the measuring instrument to perform screen color output. The revision is also very effective. However, different screens have different color gamut performances, such as the color rendering of a CRT using a cathode ray tube (with a large back on the back), the use of electron rays to stimulate the fluorescent toner, and the thin LCD LCD TFT screen, using a backlight to emit white light. The use of filters to produce color is quite different, and the color rendering of the 53LCD backlight module itself is also inconsistent. Basically, the color rendering of the screen is wider than that of the printed product, but it does not mean consistency and long-term stability. Even after 10 to 20 minutes after the power is turned on, the color will be stable. In addition, the human eye visually determines that the color has a very sensitive optic nerve and visual compensation changes. For example, when it is dark in the dark, it will be darker in the dark, and it will be adjusted in a while. This is what the user must pay attention to and understand. of.
As for the output, the print output has been the main target for a long time. The color reproduction has the plate making process, the plate condition, the printing machine condition, the ink condition, the paper medium condition, the flat printing more ink balance condition, the temperature and humidity condition and the printing. Pressure and other conditions, combined with the print version and color reproduction conditions, and the biggest pillar of color management is the stability of these conditions as the cornerstone, otherwise there are many reasons for its own conditions, then all informational color management, such as built on the beach The pavilion. The use of IT8 7-4 is the standard for future color management of output prints. The original IT8 7-3 color management color ticket tool has 928 colors and color intervals. The plate making method is used to make the IT8 7-4 color ticketing tool output the color sample under stable printing conditions, and then the measuring instrument inputs the IT8 7-4 color code data of the printing machine as a reference. Then use the IT8 7-4 file to be digitally proofed, such as the inkjet proofing machine to output the digital IT8 7-4 color sample, and then the measurement instrument to do the data input. The former is the benchmark, and the inkjet sample digital color code data is simulated. Calculate more than 1500 color scales, and trim the color △ E value of each color mark to form an ICC Profile characteristic correction file. If it is several times, it can be made similar to the IT8 7-4 color standard of the printing machine. The human eye does not see the difference △ E at 0.8. Digital proofing within ~1.5, because some pre-press departments can do contract proofing according to digital proofing, for printing test samples to be printed, in different media, paper surface, IT8 7-4 color reproduction management data should be re-edited Another set of new standards. In the event of a change in time or a change in production conditions and material conditions, the ICC Profile must be re-edited to avoid losing color reproduction standards.
Fourth, the conclusion
Today, many printing and digital printing equipments have monitoring instruments for color reproduction measurement control, and many can be automatically fed back for color reproduction adjustment. Some sheet-fed offset printing machines are equipped with offline color coding and printing. Grain measurement monitoring, as well as adjusting the feedback system, are all contributing to the stability of long-term color reproduction. However, the overall color reproduction system must be done in advance with hardware and software selection, as well as standard color reproduction data creation work, in order to have subsequent instruments to automatically control production possibilities. Today's instrument sensitivity, computer high-speed computing ability, can handle 16,000 A1 size per hour, 0.5mm print online quality monitoring per pixel, but smaller area pixels or more sensitive gap resolution, can be expected to develop, but If it is often detected that the defective rate is more than 30%, then it will be overwhelming to follow the manual to do the quality inspection. Whether to pursue accuracy and practicability, we must find a balance point, which is feasible color and quality control. system. In today's digital color management using precision color measuring instruments, the use of measuring color instruments also controls the accuracy of color correction. Therefore, the calibration and adjustment of the instrument according to regulations is also an important pillar to ensure good color management.