Detailed application of color management in the printing process
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In order to correctly and perfectly copy the design manuscript so that the color of the entire production process is consistent, it is necessary to centrally manage the color conversion and transmission through the color management mechanism. This paper explores the application of color management in the printing process.
Color management refers to the combination of software and hardware. The color is automatically and uniformly managed and adjusted during the production process to ensure color consistency. Color management is based on the chromatic space as the reference color space, using feature file to record or output color features, and using application software and third-party color management software as the user's color control tool. Through the color management scheme, various phenomena such as color distortion in the printing process can be well solved.
1. The purpose and function 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 color consistency between different displays, so that the display can accurately display the pre-product color. The effect is ultimately to achieve a high quality match of colors from scan to output.
1.2, the role of color management
Color management is efficient, mature and predictable. Through color management, professional design ability can be enhanced to better achieve the "what you see is what you get" graphic effect. The specific effects are as follows: first, to match the expected color effect; second, to achieve color consistency on different media; third, shorten the production cycle, reduce the non-performing rate; fourth, to ensure the high quality of the product Finished; fifth, the color seen on the digital print printed by the monitor or digital proofer is exactly the same as the final print.
2, the implementation process of color management
Color management requires three steps. These three steps must be performed in sequence to complement each other to achieve the desired results. These three steps are device calibration, device characterization, and conversion color space (Conversion), referred to as "3C". The three steps are described in detail below.
2.1, equipment calibration (Calibration)
As the saying goes: "If a worker wants to do something good, he must first sharpen his weapon." In order to ensure the stability and reliability of color transfer and conversion process, various input devices, display devices and output devices must be adjusted and corrected before digital printing to ensure that these devices are always at work. stable state.
One is the correction of the input device. The calibration of the input device 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 correcting the scanner, the scanner should be initialized to zero. At this time, take a piece of original for testing, and the data obtained should be exactly the same regardless of scanning at any time.
The second is the calibration of the display device. When the display is calibrated, ensure that the display characteristics of the display are consistent with the ideal parameter values set in the device file, so that the display can accurately display the color in the original.
The third is the correction of the output device. Correction of the output device is the last and most important step in the entire calibration process. Calibration of the output device includes calibration and adjustment of the printer, imagesetter, printer, and proofer. It is necessary to strictly restore the characteristics of the equipment according to the price quoted by the equipment manufacturer, which is consistent with the characteristics of the equipment at the time of shipment. In addition, it is important to pay special attention to the strict screening of the paper and the ink used for the equipment.
2.2, device characterization (Characterization)
After the device calibration is completed, the device is characterized, that is, the characteristics of all devices are recorded in detail. Different devices are recorded differently. The characterization process of the input device and the display is performed using a known standard chromaticity value table, and the chromaticity characterization curve is made according to the chromaticity value of the table and the chromaticity value generated by the input device; Characterization is the use of a space map to plot the output gamut of a device.
On the basis of making the chromaticity characteristic curve of the input device, the characterization file of the input device is made against the color space independent of the device; similarly, the characterization of the output device is made by using the gamut characteristic curve of the output device. Files, which are bridges from the device color space to the standard device-independent color space.
In general, the color profile of a device in a printing company is obtained in two ways. First, when purchasing equipment, the manufacturer will provide a profile that meets the general color management requirements of the device. The second is to use a special profile to create software and generate a color characterization file based on the actual situation of the existing equipment, but since each device, material and process will change over time, it needs to be at intervals. After that, the color characterization file is regenerated 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 description file of the device. The color gamut of the output device is narrower than that of the input device and the display. The color gamut is compressed during color conversion. Common methods include absolute chromaticity, relative chromaticity, salient saturation, and sensation. Four methods.
The first is the absolute colorimetric method. Applying the absolute colorimetric method to compress the color gamut of the output device ensures that the color in the color gamut does not change after the conversion, but replaces the color beyond the output color gamut with the color of the gamut boundary. This method is often used when the output gamut is close to the input gamut.
The second is the relative colorimetric method. The relative chromaticity method is a process of changing all colors according to white point calibration by changing the white point calibration, and does not compress the color gamut. When the gamut range is relatively close, this method is generally used for color space conversion.
The third is the salient saturation method. Outstanding saturation is the nonlinear compression of color saturation, and the focus is on the pursuit of high saturation. The goal pursued by the salient saturation method is not to be faithful to the manuscript, but to obtain a saturated color with limited equipment.
The fourth is sensory. When using color sensation for sensation, not only gamut mapping but also gradient optimization is required to maintain the relationship between colors. The sensibility is to adjust the conversion ratio according to the color rendering range of the output device, and strive for the consistency of the color in the sense.