Color space conversion is the use of device-independent color space as a bridge for color image data and conversion between different devices. The conversion of color space involves two issues. One is the choice of color mode. The description of color in the color management process should be independent of the device. The Lab color space model defined in CIE is based on a large number of color vision measurements. It is independent of the device and is therefore widely used in color management systems. The second is the mapping relationship of color space conversion. Due to the inconsistency of many color spaces, it will inevitably involve the problem of gamut compression or rejection. The colors displayed on the display screen and the colors output from the color printers, imagesetters, etc., as close as possible to the originals are the requirements and goals of the color conversion. However, because the CMYK space of the output device is narrower than the RGB space of the input and display devices such as scanners and displays, in the color space conversion, it is necessary to establish the compression and/or blanking of the color gamut that the scanner cannot cover for the ink. The relationship can ensure that the ink is as large as possible to reproduce the space in the color gamut. According to the requirements of color production and restoration, color conversion often uses the following methods. Each method is applicable to different objects.
1. Visual perception conversion. In the image copying process, the relative relationship of the original colors is maintained, that is, the conversion ratio is adjusted according to the gamut space of the output device in order to obtain a mixture of colors in the visual perception. This conversion is often used to restore higher-demanding continuous-tone originals.
2. Chroma conversion. Chroma conversion can be further divided into relative chroma conversion and absolute color conversion. The difference between the two lies in the difference in the color processing of the part of the matching color space before matching. The former replaces this part of the extra color with the border color, and the latter compresses this part of the color into the matching color space. This conversion is often used to adjust the display to ensure that the same color is obtained on different displays.
3. The best color gamut conversion. This conversion is required to produce the purest and most saturated color in the color space limited by the output device, instead of seeking to obtain the same color as the original or the display, and not aiming at the color matching between different output devices. This conversion method is often used for commercial printing with greater creativity.
In summary, to ensure maximum compatibility between desktop publishing system devices, it is necessary to implement effective color management. First, the color space of the entire system must be unified, and the unity of space must be independent of the device and color. A very wide range of Lab space or other suitable color space; secondly, the system equipment must be characterized, and the system's color profile file enables the system to coordinate and unify when transferring color information; in addition, it should be selected when performing color space conversion. Independent of the device's color description language, and based on the color gamut expressed by the printing and printing, a suitable mapping relationship can be established. At the same time, we should choose the appropriate color space conversion method according to different situations.
In general, the specific implementation of color management can be divided into two types: one is the manual management method; the other is the software management method. The so-called manual management method refers to the measurement and adjustment performed for the color control in the input and output loops, basically relying on the judgement and alertness of professionals to implement the color management methods with calibration and calibration as the main means. The so-called software management method is a color management method using a color management system in a production system. The purpose of this method is to use the device and the originals, CMS can make the color from the display to the proofs to print the same effect. The user simply presses the button and the rest is done by the computer. For example, some color management software can convert scanners, color monitors, and final proofs or printed colors, and manage them in a coordinated manner, finally achieving WYSIWYG. As long as the user operates in accordance with the requirements of the color management software, the color management software automatically performs color compensation to finally achieve the best color reproduction effect. Even with no color processing experience or expertise, it is possible to produce satisfactory color pictures. In the entire process of printing and graphic reproduction, prepress processing is the key to the entire process. Giving full play to the maximum compatibility of the performance of each device before printing and implementing the most effective color management is the most important factor in achieving excellent quality of printed products. Of the ring.
Source: HC360 HC Printing Industry Channel