The three cores of the color management system
2020-02-20 02:05:42
Color management must follow a series of prescribed processes to achieve the desired results. The color management process has three elements: Calibration, Characterization, and Contour. They are the three cores of color management.
1, equipment correction
In order to ensure the stability, reliability and sustainability of the color information transmission process, input devices, display devices, and output devices are required to be “F†to ensure that they achieve the best working conditions.
Input Correction: Corrects the input device's brightness, contrast, black and white fields (RGB balance). For example, the corrected scanner should obtain the same image data for scanning the same original document at any time.
Display correction: The display card is based on the color data of the image data and accurately displays the color on the display.
Output correction: The correction of the collation machine is based on the correct image of the monitor; the correction of the printer and the proofer must be such that the printing materials such as paper and ink used in the device meet the standards.
2, equipment characterization
As mentioned earlier, one of the cores of color management is the creation of device files. As a standard, it is a bridge between two color spaces (PCS).
Simply put, the color management system transfers the data file to the color space of the characteristic file according to the characteristic file of the input device, and then transfers the color information of the data file to the output device according to the characteristic file of the output device (display, proofer). The color space ensures consistency of color reproduction in the workflow.
3, color conversion
The third core of color management is the Color Conversion Module (CMM), which is used to interpret the device profile and perform color data conversion on different devices based on the device colors described in the profile.
A basic principle of color conversion is that the same color is guaranteed to be the same color on different devices. To achieve this, there is a device-independent color system to measure the colors on each device, and any device-dependent color space can be represented in this color space. If different device-related colors correspond to the same point in the device-independent color space, the conversion between them must be accurate. In the color conversion, color data is first converted to the device characteristics file. The color value of the PCS is then converted to the color value of other devices as needed.
The following describes the application of these three cores in color management through the specific production of input and output device ICC profiles:
â— Production of input device ICC profile
(1) IT8 standard color standard
If you want to make an ICC profile of an input device, Kodak IT8.7/1IT8.7/2 color standard (hereinafter referred to as color standard) is generally used.
IT8.7/1 and IT8.7/2 color scales for color calibration on input devices (scanners and digital cameras), IT8.7/1
The materials used with the IT8.7/2 color code are the color transparent positive film and the color paper. IT8.7/1 applies to the input color correction of the transmission scanner; IT8.7/2 applies to the input color correction of the reflection scanner.
The IT color scale consists of four parts:
1 Sample color area. This section consists of 12 x 12 color patches. According to the column, it is divided into a dark color block, a middle color block, and a bright color block, and each portion has four saturation changes.
2 color ladder feet. There are seven columns in this section, of which three columns represent cyan, magenta and yellow respectively; the other three columns represent red, green and blue respectively; the middle one is neutral.
3 neutral grey ruler. At the bottom of the color scale is a twenty-second neutral gray scale, which varies according to the degree of cosmic change. It is mainly used for basic calibration of input devices.
4 optional areas. Different manufacturers can arrange three columns according to their needs, such as trait colors. A total of 286 color patches are included on the entire color scale. These color patches are the standard color patches for creating the ICC feature folder of the scanner, which fully expresses the entire color gamut. Each color patch contains a standard colorimetric data.
(2) Production of scanner ICC profile
The production process of the scanner ICC profile is:
1 calibration
The purpose of calibration is to adjust equipment (such as scanners, monitors, printers, and printers) to a standard state to ensure that it meets production specifications. Most devices are calibrated at the factory, but during the use of the device, the quality of color reproduction is also affected due to factors such as environmental changes, aging of the device, etc. Therefore, calibration is very important for reproducing colors. All equipment must be calibrated before use.
After the scanner is turned on, it is warmed up, and then the scan drive software is run. First, the IT8 document is scanned, and the scanner's brightness, contrast, focal length, gray balance, and midtones are corrected using the gray ladder at the bottom of the IT document.
For example: to ensure the gray level of the first level in the scanned image. The RGB value is maintained between 150 and 255. The RGB value of the 22nd level, the dark part, is kept between 0 and 5, and the RGB value of the 11th level of the middle part is 125 right.
If the R, G, and B values ​​of the scanned image are inconsistent, the scanner's color cast will be described. Assume that the RGB value of the eleventh intermediate tone is actually measured as R=118, G=125, and B=125. In this case, Increase the intensity of red to balance with green and blue. This will ensure that the scanned image has a small color cast and pure color.
2 scan IT8 color standard
According to the scanner's reflection; transmission type IT8.7/1 color standard or IT8.7/2 color standard scan. Remove the descreen, sharpen, level adjustment, and other options related to color management in the scan menu, then save the scanned RGB image.
3 Generate ICC profile in ICC profile creation software
There are many softwares for making feature folders, for example: software of the company of Hyderabad and software of Agfa.
Run the ICC profile creation software, open the standard file containing the color block color data and the scanned image file in the software. The software will compare and correct the RGB data in the image file with the Lab color data of the color block standard. Optimize, get the characteristic file of the scanner, save this file finally, finish making the ICC characteristic file of the input apparatus.
In this ICC profile i' records the basic characteristics of the scanner's color reproduction. Different scanners have different ICC profiles. It can be seen that the role of the IT8 color scale in the production of ICC profiles is like a rule to measure the accuracy of color.
1, equipment correction
In order to ensure the stability, reliability and sustainability of the color information transmission process, input devices, display devices, and output devices are required to be “F†to ensure that they achieve the best working conditions.
Input Correction: Corrects the input device's brightness, contrast, black and white fields (RGB balance). For example, the corrected scanner should obtain the same image data for scanning the same original document at any time.
Display correction: The display card is based on the color data of the image data and accurately displays the color on the display.
Output correction: The correction of the collation machine is based on the correct image of the monitor; the correction of the printer and the proofer must be such that the printing materials such as paper and ink used in the device meet the standards.
2, equipment characterization
As mentioned earlier, one of the cores of color management is the creation of device files. As a standard, it is a bridge between two color spaces (PCS).
Simply put, the color management system transfers the data file to the color space of the characteristic file according to the characteristic file of the input device, and then transfers the color information of the data file to the output device according to the characteristic file of the output device (display, proofer). The color space ensures consistency of color reproduction in the workflow.
3, color conversion
The third core of color management is the Color Conversion Module (CMM), which is used to interpret the device profile and perform color data conversion on different devices based on the device colors described in the profile.
A basic principle of color conversion is that the same color is guaranteed to be the same color on different devices. To achieve this, there is a device-independent color system to measure the colors on each device, and any device-dependent color space can be represented in this color space. If different device-related colors correspond to the same point in the device-independent color space, the conversion between them must be accurate. In the color conversion, color data is first converted to the device characteristics file. The color value of the PCS is then converted to the color value of other devices as needed.
The following describes the application of these three cores in color management through the specific production of input and output device ICC profiles:
â— Production of input device ICC profile
(1) IT8 standard color standard
If you want to make an ICC profile of an input device, Kodak IT8.7/1IT8.7/2 color standard (hereinafter referred to as color standard) is generally used.
IT8.7/1 and IT8.7/2 color scales for color calibration on input devices (scanners and digital cameras), IT8.7/1
The materials used with the IT8.7/2 color code are the color transparent positive film and the color paper. IT8.7/1 applies to the input color correction of the transmission scanner; IT8.7/2 applies to the input color correction of the reflection scanner.
The IT color scale consists of four parts:
1 Sample color area. This section consists of 12 x 12 color patches. According to the column, it is divided into a dark color block, a middle color block, and a bright color block, and each portion has four saturation changes.
2 color ladder feet. There are seven columns in this section, of which three columns represent cyan, magenta and yellow respectively; the other three columns represent red, green and blue respectively; the middle one is neutral.
3 neutral grey ruler. At the bottom of the color scale is a twenty-second neutral gray scale, which varies according to the degree of cosmic change. It is mainly used for basic calibration of input devices.
4 optional areas. Different manufacturers can arrange three columns according to their needs, such as trait colors. A total of 286 color patches are included on the entire color scale. These color patches are the standard color patches for creating the ICC feature folder of the scanner, which fully expresses the entire color gamut. Each color patch contains a standard colorimetric data.
(2) Production of scanner ICC profile
The production process of the scanner ICC profile is:
1 calibration
The purpose of calibration is to adjust equipment (such as scanners, monitors, printers, and printers) to a standard state to ensure that it meets production specifications. Most devices are calibrated at the factory, but during the use of the device, the quality of color reproduction is also affected due to factors such as environmental changes, aging of the device, etc. Therefore, calibration is very important for reproducing colors. All equipment must be calibrated before use.
After the scanner is turned on, it is warmed up, and then the scan drive software is run. First, the IT8 document is scanned, and the scanner's brightness, contrast, focal length, gray balance, and midtones are corrected using the gray ladder at the bottom of the IT document.
For example: to ensure the gray level of the first level in the scanned image. The RGB value is maintained between 150 and 255. The RGB value of the 22nd level, the dark part, is kept between 0 and 5, and the RGB value of the 11th level of the middle part is 125 right.
If the R, G, and B values ​​of the scanned image are inconsistent, the scanner's color cast will be described. Assume that the RGB value of the eleventh intermediate tone is actually measured as R=118, G=125, and B=125. In this case, Increase the intensity of red to balance with green and blue. This will ensure that the scanned image has a small color cast and pure color.
2 scan IT8 color standard
According to the scanner's reflection; transmission type IT8.7/1 color standard or IT8.7/2 color standard scan. Remove the descreen, sharpen, level adjustment, and other options related to color management in the scan menu, then save the scanned RGB image.
3 Generate ICC profile in ICC profile creation software
There are many softwares for making feature folders, for example: software of the company of Hyderabad and software of Agfa.
Run the ICC profile creation software, open the standard file containing the color block color data and the scanned image file in the software. The software will compare and correct the RGB data in the image file with the Lab color data of the color block standard. Optimize, get the characteristic file of the scanner, save this file finally, finish making the ICC characteristic file of the input apparatus.
In this ICC profile i' records the basic characteristics of the scanner's color reproduction. Different scanners have different ICC profiles. It can be seen that the role of the IT8 color scale in the production of ICC profiles is like a rule to measure the accuracy of color.
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