The printing process is actually the process of transferring the image information of the original image in various printing input/output devices in various printing input/output devices, how to realize the maximum compatibility between the input and output of the information from the original information. Sex and consistency, that is, to ensure the accuracy of information transmission, to achieve the best reproduction of the original.
In order to be copied, the printing manuscript must first be color-separated. The current color separation technology has evolved from traditional photo separation and electronic color separation to the current desktop publishing system.
The color printing and printing process of the desktop publishing system is essentially the process of converting the color information of the original image through various devices and different color spaces to restore the color. The reproduction of color depends on the device that generates it, but in the integrated environment of desktop publishing system, because each device has different color gamut and color characteristics, the precise control and transmission of graphic color information in desktop publishing system It is especially difficult. What you see is the ultimate goal of the original copy. To achieve this goal, effective color management independent of the device must be implemented in the desktop publishing system to ensure the compatibility of signal input and output between devices, reduce and compensate for the device. The difference in color characteristics and the influence of the color mode on the color information, so that the color data information of the graphic text is minimized when the color data information is transferred between different color spaces and devices with different color characteristics, so as to ensure the color of the same picture from the input. The effects displayed in the display and then in the output are matched as closely as possible to achieve a harmonious color between the reproduction and the original.
To do a good job of color management in the desktop publishing system, the key is to deal with the unified color space, device system characterization and color conversion.
Guarantee the unification of color mode and its color space
In desktop publishing systems, color reproduction often involves three color modes: RGB, CMYK, and Lab. RGB is a color mode of color light. It consists of three channels: red, green and blue. In this mode, other colors are formed by superimposing these three primary colors. Since these three colors have 256 brightness levels, the three-color overlay can form 16.7 million colors. In desktop publishing systems, input and display devices such as scanners, digital cameras, and displays rely on this mode to express colors. When the sun shines on an object, the object absorbs part of the light and reflects other light. Reflected light is the color of the object we see, which is a subtractive mode. Depending on this color reduction method, the CMYK mode suitable for printing and printing has evolved. Since the inks of these three colors are difficult to superimpose true black in practice, black is introduced during printing and printing to enhance the dark tone and deepen the dark color. Although this color mode defines a much smaller color than the color defined by RGB, that is, the color space is much smaller, the output devices such as imagesetters, printers, and proofers in the desktop color prepress system depend on this mode. To reproduce the color. Lab mode is a color mode developed by CIE (International Commission on Illumination). Any color in nature can be expressed in Lab space, and its color space is larger than RGB space. In addition, this mode is a digital way to describe human visual sensing, independent of the device, so it makes up for the RGB and CMYK modes must rely on the lack of color characteristics of the device.
Because Lab's color space is larger than the color space of RGB mode and CMYK mode. This means that the color information that RGB and CMYK can describe can be mapped in Lab space. Therefore, in the color management of the desktop publishing system, if all the color conversion and color correction operations are completed based on the Lab space, when the color data is converted from the Lab space to the RGB or CMYK space, the color will not be caused by the insufficient amount of data. deviation. It can be seen that in the color management, in order to make the color space uniform, the Lab mode which is independent of the device and has a large color space should be used as a reference.
In summary, in the pre-press production process, we should store the color information obtained by the scanner and digital camera working in RGB mode in Lab mode, and perform color editing and correction in the Lab color space. Convert to CMYK space when printing or filming. This is the best solution for color processing. Since printers and imagesetters express colors in CMYK mode, in practice, many operators are also accustomed to performing in CMYK space when editing correction colors. This is not desirable because it causes color loss, and operation in CMYK can slow down the computation from the computer.
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