The printing process is actually an image on the original document. In various types of print input/output devices, the original image information is transmitted, how to realize the maximum compatibility between the input and output devices, and the amount of input/output information from the original information. Sexuality and consistency, that is, to ensure the accuracy of information transmission as possible, to achieve faithful to the best copy of the original.
To print the manuscripts to be copied, the color separation must be carried out first. Now the color separation technology has evolved from the traditional photographic color 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 graphic and text through various devices and different color spaces so that the color can be restored. The color reproduction depends on the device that produced it, but in the integrated environment of the desktop publishing system, since each device has a different color gamut and color characteristics, the graphic color information is precisely controlled and transmitted in the desktop publishing system. It is particularly difficult. What you see is the ultimate goal of copying the original document. To achieve this goal, you must implement effective device-independent color management in the desktop publishing system to ensure the compatibility of input and output signals between devices, and to reduce and compensate for devices. The difference of color characteristics and the influence of different color modes on the color information, so that the color information of the graphic color data is transferred between different color spaces and devices having different color characteristics, and the color distortion is minimized so as to ensure that the color of the same picture is input. The effects shown in the display and then in the output are matched as much as possible, so that the reproduction and the original color are in harmony.
To do a good job in the color management of desktop publishing systems, the key is to handle the unified color space, device system characterization and color conversion and other links.
Guarantee the unity of color modes and their color space
In the desktop publishing system, color reproduction often involves three color modes of 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 the superposition of these three primary colors. Since all three colors have 256 luminance levels, three color overlays can create 16.7 million colors. In desktop publishing systems, the input and display devices such as scanners, digital cameras, and displays rely on this mode to express colors. When sunlight strikes an object, it absorbs some of the light and reflects it. Reflected light is the color of the object we see. This is a subtractive mode. Relying on this color reduction method, CMYK patterns suitable for printing and printing have evolved. Since in reality these three colors of ink are difficult to superimpose true black, black is introduced during printing and printing to enhance dark tone and darken the dark colors. Although the color defined by this color mode is much less than that defined by RGB, that is, the color space is much smaller, output devices such as imagesetter, printer, and proofer in the desktop color prepress system depend on this mode. To reproduce color. The Lab mode is a color model developed by the CIE (International Commission on Illumination). Any color in the natural world can be expressed in Lab space, and its color space is larger than RGB space. In addition, this model is a digital way to describe the human visual sense, and has nothing to do with the device, so it makes up for the lack of RGB and CMYK modes that must rely on the device's color characteristics.
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 desktop publishing system's color management, if all color conversion and color correction jobs are based on Lab space, when color data is converted from Lab space to RGB or CMYK space, color data will not be caused due to insufficient data volume. deviation. From this we can see that in the color management, to make the color space can be unified, it should be based on this Lab-mode that is independent of the device and has a large color space.
In summary, in the prepress production process, we should store the color information obtained by scanners and digital cameras working in RGB mode in Lab mode, and perform color editing and correction in the Lab color space. When printing or filming, it is converted to CMYK space. This is the best solution for color processing. Because the printer and the photo-composing machine express colors in the CMYK mode, in practice, many operators are also accustomed to performing in the CMYK space when editing corrected colors. This is undesirable because it can cause color loss. Operating in CMYK can also slow down the calculation from the computer.