A solution to the problem of digital color quality control - color management technology (2)
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Device Characterization - It is used to define the range of colors that the input device can recognize and the range of colors that the output device can replicate. In this way, the corrected input or output device can capture or copy the image accordingly. After the program described by the device color characteristics, the result is stored in the "profile". So Profile is a digital data file used to describe the color characteristics of media devices; and International Color Association ICC provides a set of profile standards that industry can follow. As long as the profiles of various devices conform to ICC standards, colors such as ColorSy nc can be utilized. Management software to achieve the purpose of color reproduction [Gentile, 1995].
Color space conversion (Conversion) - based on the numerical data of the "color profile" of various devices, the color data data of the image is determined by "Device-Dependentcolor space" (such as RGB or CYMK color space) is translated into the "Device-Independent color space" (such as CIEXYZ color space) process; in practical applications, the coordinate system of each media device dependent color space and device independent color space is The mathematical mode of the way to establish a conversion relationship between the two.
Environmental Construction and System Assessment
When importing a color management system, you must have the following tools and instruments:
1. ICC Profile (ICC Profile)
2. Macintosh: Color Sync 2.5 or Windows: ICM2.0
3. Color Space Conversion Engine (Color Engine) such as: Agfa, Heidelberg, Kodak, etc.
4.IT8.7 standard scanning original and its standard data:
(1) IT8.7/1 [standard scan transmission original] and its standard data
(2) IT8.7/2 [standard scanning reflection original] and its standard data
(3) IT8.7/3 [928-standard electronic file for standard output] and its standard data
5. An application that generates an ICC color profile, for example: ColorTune 3.01Pro, LinoColor, Colorblind and other related software
6. Color measuring instruments, for example: Gretag-Macbeth Spectrolino & Spectroscan, etc.
7. Support image processing or layout software for inserting ICC color description files, for example: Adobe Photoshop 5.0 Or PageMaker 6.5C
8. A dot processor (RIP) that supports the calculation of ICC color profiles
The ICC International Color Organization was established in 1993 to establish a standard format for ICCProfile color characterization files. A variety of color conversion data messages are included in the ICC Profile color characterization file (Required Tag Data). The main function is to provide the necessary basic standard data content information when the color management system performs color conversion (Conversion), which means that as long as it is an ICC Profile, it must have such information to provide color management system operations, and the source of these data is mainly It is from the IT8.7 color control guide (as shown in Figure 1).
The IT8.7/1 color control guide is a standard scan transmissive manuscript and its standard data applied to the input device, while IT8.7/2 is a standard scan reflex manuscript and its standard data applied to the input device. The IT8.7/3 color control guide is a standard original applied to the output device. The color block data contained in the IT8.7/3 control guide is mainly composed of cyan (C), magenta (M), and yellow ( Y), black (K) and other four main printing colors, the percentage of CMYK dots in each color block position is different, so each device is through the IT8.7/3 control guide printout The specified way to output the dot percentage of each color block, and the above printed 928 color data data can represent the color rendering ability of the output device.
All calibrated color output devices read color data from the IT8.7/3 control guide printed on the device by color measurement instruments (such as Gretag-Macbeth Spectrolino & Spectroscan, X-Rite Spectrofiler, etc.) to create RGB or CMYK Forward (R orward) and reverse (R everse) modes between CIE XYZ or CIE Lab. The so-called Forward mode mainly deals with the results of RGB or CMYK signals corresponding to CIEXYZ or CIE Lab, and produces various corresponding modes such as Perceptual, Relative Colorimetric, and Absolute Colorimetric. ) and saturation (Saturation) and other color correspondence data; and the reverse mode is to use the Forward mode to establish the CIE XYZ or CIE Lab signal corresponding to RGB or CMYK results, these results are Placed in the required data index area (Required Tag Data) in the color characterization file, and the result is converted into a format that conforms to the ICC standard, and then combined with the relevant information developed by the ICC to be stored, it becomes us usable. Color profile file (profile). Therefore, the "color characterization file" is a digital data file describing the color characteristics of the media device, and its main purpose is to establish the relationship between RGB or CMYK and CIE XYZ or CIELab.
In addition, the IT8.7/3 control guide color information results are converted into a color profile description file that conforms to the ICC standard format, which is a profile generator or profile generator in a general color management system, such as Agfa. Color Tune 3.01Pro, Kodak's ColorFlow, Heidelberg's LinoColor and other related software, currently in the world's relevant color quality control vendors have developed such software, the reference data is attached as shown in Table 1.
On the PC 98/NT4.0 operating platform of the PC personal computer, the ICM 2.0 file format (Image Color Management) is used to support the storage and application of the ICC profile; on the Apple Macintosh operating platform, the color is utilized. Sync2.5 file format to support ICC Profile.
As for the evaluation of the color management system, there is currently no measurement standard and no quantitative indicator data. The following only proposes the recommendations of foreign scholars and experts for reference:
1. Whether the color profile of the device is generated by the user
2. Whether the color profile of the input device conforms to the international ISO IT8.7 standard, and it provides the type version (transmission, reflection, etc.)
3. When the color profile of the output device is established, the number of patches is measured.
4. Is the instrument for measuring the color block compatible with the color management system?
5. The price of the color management system
6. Is there an educational training course after purchasing the color management system?
7. Does the color management system support soft proofing or hard proofing?
The above are questions that should be considered when evaluating the color management system. Since the introduction of color management technology requires manpower, time and money, should the industry carefully consider what its needs are before it is imported? What color problems do you want to solve on your device? Is there a considerable willingness to invest in the digital printing process and the field of network printing? This will not cause confusion in the process and waste of investment.