To copy the design manuscript correctly and completely, so that the consistency of color appearance in the entire production process, the conversion and transmission of colors must be centrally managed through the mechanism of color management. This article explores the application of color management in the printing process.
Color management refers to the method of combining software and hardware to automatically and uniformly manage and adjust colors in the production process, thereby ensuring the consistency of colors. Color management refers to the chromaticity space as the reference color space, uses feature files to record or output color features, and uses application software and third-party color management software as users' color control tools. Through the color management scheme, various phenomena such as color distortion in the printing process can be well solved.
1. The purpose and role of color management
1.1 The purpose of color management
The purpose of color management is to achieve color matching between different devices for various scanners, cameras, printers, proofers, printing machines, etc., to ensure the consistency of colors between different displays, so that the display can accurately display the pre-product colors The result is to achieve high-quality color matching at all stages from scanning to output.
1.2 The role of color management
Color management has high efficiency, maturity and predictability, through color management can enhance professional design capabilities, and better achieve "what you see is what you get" graphic effects. The specific functions are as follows: first, it matches the expected color effect; second, it can achieve the consistency of colors on different media; third, it shortens the production cycle and reduces the defect rate; fourth, guarantees the high quality of the product Done; Fifth, the color seen on the digital manuscript printed on the monitor or digital proofer can be completely consistent with the color of the final printed matter.
2. The implementation process of color management
There are three steps to carry out color management. These three steps must be carried out in sequence and complement each other to achieve the desired effect. These three steps are equipment calibration (Calibration), equipment characterization (Characterization), conversion color space (Conversion), referred to as "3C". The following describes these three steps in detail.
2.1, equipment calibration (Calibration)
As the saying goes: "Workers must first sharpen their tools if they want to do their best." To ensure the stability and reliability of colors in the process of transfer and conversion, before digital printing, various input devices, display devices, and output devices must be adjusted and corrected to ensure that these devices are always in operation stable state.
One is the calibration of the input device. Input device calibration refers to the adjustment and calibration of the brightness, contrast, and black and white fields of all input devices to be used. For example, after the scanner is calibrated, the scanner should be initialized to zero. At this time, take a manuscript to test, no matter what time it is scanned, the data obtained should be exactly the same.
The second is the calibration of the display device. When the monitor is calibrated, ensure that the display characteristics of the monitor are consistent with the ideal parameter values ​​set in the device file, so as to ensure that the display can accurately display the colors in the original.
The third is the correction of the output device. The calibration of the output device is the last link in the entire calibration process and the most important step. Correction of output devices includes calibration and adjustment of printers, imagesetters, printing presses, and proofers. It is necessary to restore the characteristics of the equipment in strict accordance with the inquiry price provided by the equipment manufacturer. The equipment is consistent with the characteristics at the time of shipment. In addition, special attention should be paid to the strict selection of the paper and the ink used in the equipment.
2.2, Device Characterization (Characterization)
After the device calibration is completed, the device characterization process is performed, that is, the characteristics of all devices are recorded in detail. Different devices have different recording methods. Characterization of input devices and displays is accomplished using a known standard chromaticity value table, and a chromaticity characteristic curve is produced based on the chromaticity values ​​of the table and the chromaticity values ​​generated by the input device; The characterization process is to use the space map to draw the output color gamut characteristic curve of the device.
Based on the chromaticity characteristic curve of the input device, the characteristic description file of the input device is made against the color space independent of the device; similarly, the characteristic description of the output device is made using the color gamut characteristic curve of the output device Files, these description files are the bridges from the device color space to the standard device-independent color space.
In general, the color profile of equipment in printing companies is obtained through the following two methods. First, when purchasing a device, the manufacturer will provide a profile, which can meet the general color management requirements of the device. The second is to use special profiles to create software and generate color feature description files according to the actual situation of existing equipment. However, since each equipment, material and process will change with time, it needs to be done every once in a while Then regenerate the color feature description file to adapt to the actual color corresponding situation.
2.3. Conversion color space (Conversion)
After correcting and characterizing the device, the standard device-independent color space is used as the medium, and the color space of each device is correctly converted according to the device description file. The color gamut of the output device is narrower than that of the input device and the display, and the color gamut is compressed when performing color conversion. Common methods include absolute chromaticity method, relative chromaticity method, highlight saturation method, and sensibility. Four methods.
The first is the absolute chromaticity method. Using the absolute chromaticity method to compress the color gamut of the output device can ensure that the colors in the color gamut will not change after conversion, but instead replace the colors beyond the output color gamut with the colors of the color gamut boundary. This method is often used when the output color gamut is similar to the input color gamut.
The second is relative colorimetry. The relative chromaticity method is to realize the process that all colors change correspondingly according to the white point calibration by changing the white point calibration, and the color gamut is not compressed. When the color gamut range is relatively close, this method is generally used for color space conversion.
The third is the outstanding saturation method. Highlighting saturation is a non-linear compression of the saturation of the color, and the focus is on the pursuit of high saturation. The goal pursued by the highlight saturation method is not to be loyal to the original, but to obtain saturated colors with limited equipment.
The fourth is sensory. When using perceptual color compression, not only color gamut mapping, but also gradient optimization, to maintain the mutual relationship between colors. Perception is to adjust the conversion ratio according to the color rendering range of the output device, and strive for the consistency of color in perception.
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