(1) ICC profile
In the color printing process, I often hear the prepress operator saying: The printing plate we made is very good, but unfortunately the printing was given to the batch. The printing operator has another argument, what is the printing plate! The deep place is not deep, the shallow place is not shallow, it is impossible to print!
Why are there two different sounds? The reason:
(1) There is a difference between the color on the computer screen and the color printed on the paper:
(2) The same card signed by the customer does not match the printed sample;
(3) The influence of various materials and equipment on color.
It seems that color management is first and foremost a matter of color space, that is, based on which color space is used for color control. Display, digital camera, scanner, etc. all work in the RGB color space; proofers, printers, etc. all work in the CMYK color space. When the same image is output on these devices, the final color effect may be different. This is because they are in different color spaces.
Since RGB and CMYK are all space related to the device, it is necessary to realize the conversion of different device space color modes to ensure that the colors of the same image color from the input, display to output are matched as much as possible, and finally the original and the duplicate are achieved. Consistent. It is necessary to establish a color space that is independent of any specific equipment, materials, and processes.
In the color management technology, the color space of CIEl976Lab is adopted, and the color of any device can be converted into this space, and then the color matching conversion is performed.
To illustrate more clearly the role of the CIEl976Lab color space, look at an example:
In actual life, we often go to the farmer's market to buy food. We will find that there is a counterweight at the exit of the farmer's market, and it is the only one. This is the industrial and commercial department set up to manage the farmer's market and prevent the shortage of traders. If the buyer buys that the food he bought is not enough, he can go to the weighing platform to re-scale. This is a standard scale. This standard scale has nothing to do with the scale of any trader. Any trader must follow this scale. standard.
In color management, it is necessary to understand the color rendering characteristics of colors on various devices by presenting the colors presented on one device to another device with high fidelity. Since the device-independent color space, ie CIEl976I plus color space, has been selected, the color characteristics of the device are expressed as follows: the device's description of the color has a certain correspondence with the color value of the "universal" color space. Is the color profile of the device. Or called an ICC profile.
The ICC profile can be divided into: ICC profile of input device, display device and output device.
Note:
1RGB color space
A color space composed of a mixture of colors of three primary colors of red, green, and blue. The colors used by the scanner and display are composed of three primary colors of red, green and blue. The RGB color space is a device-dependent color space. That is to say, the colors they produce are related to the specific device used, and the color mixing rule in the RGB color space conforms to the color-adding method.
2CMYK color space
The CMYK color space is the space formed by the color material and conforms to the principle of color subtraction. The CMYK color space is also a space associated with the device.
Note: CIEl976Lab Chroma Space CIE: International Illumination Commission French Head L is a description of the color brightness a is to describe the degree of reddish green color.
b is the degree to which the color is yellowish and bluish.
Note: ICC is the Intermatconal color consoertion [next]
(ii) Three cores of the color management system (3C)
Color management must follow a set of prescribed processes to achieve the desired results. The color management process has three elements: device calibration, characterization, and color conversion (Conuersion). 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, it is required to perform the "F" on the input device, the display device, and the output device to ensure that they reach the optimal working state.
Input correction: Corrects the brightness, contrast, and black-and-white field (RGB balance) of the input device. For example, the corrected scanner should obtain the same image data for the same original regardless of when it is scanned.
Display calibration: The display card accurately displays the color on the display according to the color data of the image data.
Output correction: The calibration of the alignment machine is based on the correct image of the display; for the correction of the printing machine and the proofing machine, the printing materials such as paper and ink used in the equipment must conform to the standard.
2, equipment characterization
As mentioned earlier, one of the cores of color management is the creation of device files, which serve as a standard for two color space bridges (PCS).
Simply put, the color management system transfers the data file to the color space of the feature file according to the characterization 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 the 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 device profile files and perform color data conversion for 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 color on each device, and any device-dependent color space can be represented in this color space. If different device-dependent colors correspond to the same point in the device-independent color space, then the conversion between them must be accurate. When color conversion is performed, the color data is first converted to the device property file. The color value of the PCS is converted to the color value of other devices as needed.
The following is a description of the application of these three cores in color management through the specific production of ICC profiles of input and output devices:
â— Production of input device ICC profile
(1) IT8 standard color standard
If you want to make an ICC profile for an input device, you should generally use the Kodak IT8.7/1 IT8.7/2 standard color code (hereinafter referred to as the color code).
IT8.7/1 and IT8.7/2 color scales for color calibration of input devices (scanners and digital cameras), IT8.7/1
The materials used in the IT8.7/2 color scale are color transparent positive and color photographic paper. IT8.7/1 is suitable for input color correction of transmissive scanners; IT8.7/2 is suitable for input color correction of reflective scanners.
The IT color scale consists of four parts:
1 sample color area. This part consists of 12 x 12 color blocks. According to the column, it is divided into dark toning blocks, intermediate toning blocks, and bright toning blocks, each of which has four saturation changes.
2 color ladders. There are seven columns in this section, three of which represent cyan, magenta, and yellow; the other three columns represent red, green, and blue; the middle column is neutral.
3 neutral gray ladder. At the bottom of the color scale is a twenty-two neutral neutral gray scale that varies by degree. Mainly used for basic correction of input devices.
4 optional areas. Different manufacturers can arrange three columns according to their own needs, such as feature colors. There are 286 color blocks on the entire color scale. These color patches are the standard color patches that create the scanner's ICC properties folder, which fully express the entire color gamut, and each color block contains a standard color data.
(2) Production of scanner ICC profile
The scanner ICC profile is created as follows:
1 The purpose of calibration calibration is to adjust equipment (such as scanners, monitors, printers, and printers) to a standard state to ensure that it meets production specifications. Most of the equipment is calibrated at the factory, but the quality of color reproduction is affected by factors such as environmental changes and equipment aging during use. Calibration is therefore important for reproducing colors. All equipment must be calibrated before it can be used.
After the scanner is turned on, it is warmed up, and then the scan driver software is run. First, the IT8 original is scanned, and the scanner's brightness, contrast, focal length, gray balance and midtone are corrected by the gray scale at the bottom of the IT original.
For example: to ensure that the gray ladder first level in the scanned image. The RGB value is maintained between 150 and 255. The RGB value of the 22nd level, that is, the dark adjustment part is maintained between 0 and 5. The RGB value of the eleventh stage of the middle part is 125 right.
If the R, G, and B values ​​of the scanned image are inconsistent, the scanner is color cast. It is assumed that the RGB value of the eleventh level of the intermediate adjustment is actually measured as R=118, G=125, and B=125. Increase the red intensity to balance with green and blue. This can ensure that the scanned image has a smaller color cast and a pure color.
2 Scan the IT8 color scale according to the reflection of the scanner; the transmission type selects the IT8.7/1 color standard or the IT8.7/2 color standard scan. In the scan menu, uncheck the net, sharpen, level adjustment and other options related to color management, and then save the scanned RGB image.
3 There are many softwares for generating ICC profile creation feature folders in ICC profile creation software, for example: Heidelberg software, Agfa software.
Run the ICC property file creation software, open the standard file containing the color block chromaticity data and the scanned image file in the software. The software compares and corrects the RGB data in the image file with the Lab color chromaticity data of the color block standard. Optimize to get the scanner's property file, and finally save the file to end the production of the input device ICC profile.
In this ICC profile, i' records the basic characteristics of the color reproduction of this scanner. Different scanners have different ICC profiles. It can be seen that the IT8 color scale acts as a ruler for measuring the accuracy of color in the process of making ICC profiles.
Production of output device ICC profile
(1) IT8.7/3 digital standard color standard If the ICC characteristic file of the output device is to be produced, the IT8.7/3 digital standard color standard (hereinafter referred to as the color standard) is indispensable. The IT8.7/3 color standard is an electronic file suitable for output devices that use CMYK four colors for color performance.
A total of 928 different color blocks are included in the IT8.7/3 color standard. The color data of these color blocks are all CMYK data, and the CMYK dot coverage of each color block is different. When different output devices output the IT8.7/3 color standard, the 928 colors printed represent the output device. Color performance. Devices with strong color performance can show subtle differences between the blocks; while devices with poor color performance have fewer differences between patches, and the small differences between the patches are unclear. The ability of the output device to reproduce the IT8.7/3 color scale represents the output accuracy of the device.
On the IT8.7/3 color scale, the following different types of areas are included:
1 dark toner block area.
2 overprint color block area (check ink overprint effect j
3 does not contain black saturated color block area.
4 contains 20% black saturated color block area.
5 Gray area consisting of CMY or CMYK (check gray balance).
6 solid color block color area (to check the density of the field).
7CMYK ladder (check the dot coverage).
(2) The production process of the output device ICC profile
Take the printing equipment as an example: Explain the production of the ICC profile of the output device.
1 Calibration Before the official printing of the IT8.7/3 color standard, the control device is used to calibrate the printing equipment, mainly referring to the solid density and dot coverage. The environment and production conditions of the printing press are required to be stable. For example, the solid density and dot coverage in official production must be consistent with the printing of the IT8.7/3 color standard. Only the ICC profile generated in this way can correctly reflect this. The color characteristics of the press.
2 Printing IT8.7/3 color standard will output the IT8.7/3 color standard and get proofs by printing. In addition, the film output and the printing process are adjusted to the standard state.
3 In the ICC profile creation software to generate ICC profile to run the ICC profile creation software, select the measurement options, generally online automatic measurement, the scanning spectrophotometer is driven, according to the prompts for color measurement of IT8.7/3 printed proofs After the measurement is finished, the software accurately compares the measured chromaticity data with the CMYK data of the color block in the color standard, and generates the ICC characteristic file of the output device by the software. Save this ICC profile.
Unlike a scanner that has only one ICC profile, a single press may have multiple ICC profiles because if the paper, ink, dot, and environmental conditions change, it will have an effect on color, so it must be Make multiple ICC profiles for different paper and ink combinations to meet your production needs.
If each device associated with color reproduction has an ICC profile, it provides the necessary foundation for color copy consistency. The following is only a screen soft proof to illustrate the importance of ICC profiles in color reproduction. A color job must be sampled before it is officially printed. One of the functions of proofing is to check the quality of the color on the sample. If the error can be found before the official printing, the cost can be reduced, and the preview can be previewed to the actual printing. What about the color effect?
The display is completely different from the mechanism for printing and reproducing colors. The red, green and blue colors are generated on the display screen, which are colored in the color-light mixing mode, and the yellow, magenta, cyan and black colors used in the four-color printing are four. The ink is colored in a color mixing mode; the color gamut of the two devices is also different. Therefore, the color seen on the display actually has a large difference from the color on the final print.
The basic principle of screen soft proofing:
Display - Display (ICC) - Color Management (CMM) - Printing Machine (ICC) Printing Machine
However, if there are ICC profiles for the display and printing equipment and the color conversion module (CMM), the color of the final print can be previewed in advance through the display. Since the ICC profile contains the characteristics of the device's reproduction color, the color management software will compare the ICC profile of the two devices to determine whether the color in the image file can be printed. If there is a super color gamut color, the color tube software will convert the super gamut color so that the final print color effect can be correctly previewed on the display.
(1) ICC profile
In the color printing process, I often hear the prepress operator saying: The printing plate we made is very good, but unfortunately the printing was given to the batch. The printing operator has another argument, what is the printing plate! The deep place is not deep, the shallow place is not shallow, it is impossible to print!
Why are there two different sounds? The reason:
(1) There is a difference between the color on the computer screen and the color printed on the paper:
(2) The same card signed by the customer does not match the printed sample;
(3) The influence of various materials and equipment on color.
It seems that color management is first and foremost a matter of color space, that is, based on which color space is used for color control. Display, digital camera, scanner, etc. all work in the RGB color space; proofers, printers, etc. all work in the CMYK color space. When the same image is output on these devices, the final color effect may be different. This is because they are in different color spaces.
Since RGB and CMYK are all space related to the device, it is necessary to realize the conversion of different device space color modes to ensure that the colors of the same image color from the input, display to output are matched as much as possible, and finally the original and the duplicate are achieved. Consistent. It is necessary to establish a color space that is independent of any specific equipment, materials, and processes.
In the color management technology, the color space of CIEl976Lab is adopted, and the color of any device can be converted into this space, and then the color matching conversion is performed.
To illustrate more clearly the role of the CIEl976Lab color space, look at an example:
In actual life, we often go to the farmer's market to buy food. We will find that there is a counterweight at the exit of the farmer's market, and it is the only one. This is the industrial and commercial department set up to manage the farmer's market and prevent the shortage of traders. If the buyer buys that the food he bought is not enough, he can go to the weighing platform to re-scale. This is a standard scale. This standard scale has nothing to do with the scale of any trader. Any trader must follow this scale. standard.
In color management, it is necessary to understand the color rendering characteristics of colors on various devices by presenting the colors presented on one device to another device with high fidelity. Since the device-independent color space, ie CIEl976I plus color space, has been selected, the color characteristics of the device are expressed as follows: the device's description of the color has a certain correspondence with the color value of the "universal" color space. Is the color profile of the device. Or called an ICC profile.
The ICC profile can be divided into: ICC profile of input device, display device and output device.
Note:
1RGB color space
A color space composed of a mixture of colors of three primary colors of red, green, and blue. The colors used by the scanner and display are composed of three primary colors of red, green and blue. The RGB color space is a device-dependent color space. That is to say, the colors they produce are related to the specific device used, and the color mixing rule in the RGB color space conforms to the color-adding method.
2CMYK color space
The CMYK color space is the space formed by the color material and conforms to the principle of color subtraction. The CMYK color space is also a space associated with the device.
Note: CIEl976Lab Chroma Space CIE: International Illumination Commission French Head L is a description of the color brightness a is to describe the degree of reddish green color.
b is the degree to which the color is yellowish and bluish.
Note: ICC is the Intermatconal color consoertion [next]
(ii) Three cores of the color management system (3C)
Color management must follow a set of prescribed processes to achieve the desired results. The color management process has three elements: device calibration, characterization, and color conversion (Conuersion). 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, it is required to perform the "F" on the input device, the display device, and the output device to ensure that they reach the optimal working state.
Input correction: Corrects the brightness, contrast, and black-and-white field (RGB balance) of the input device. For example, the corrected scanner should obtain the same image data for the same original regardless of when it is scanned.
Display calibration: The display card accurately displays the color on the display according to the color data of the image data.
Output correction: The calibration of the alignment machine is based on the correct image of the display; for the correction of the printing machine and the proofing machine, the printing materials such as paper and ink used in the equipment must conform to the standard.
2, equipment characterization
As mentioned earlier, one of the cores of color management is the creation of device files, which serve as a standard for two color space bridges (PCS).
Simply put, the color management system transfers the data file to the color space of the feature file according to the characterization 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 the 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 device profile files and perform color data conversion for 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 color on each device, and any device-dependent color space can be represented in this color space. If different device-dependent colors correspond to the same point in the device-independent color space, then the conversion between them must be accurate. When color conversion is performed, the color data is first converted to the device property file. The color value of the PCS is converted to the color value of other devices as needed.
The following is a description of the application of these three cores in color management through the specific production of ICC profiles of input and output devices:
â— Production of input device ICC profile
(1) IT8 standard color standard
If you want to make an ICC profile for an input device, you should generally use the Kodak IT8.7/1 IT8.7/2 standard color code (hereinafter referred to as the color code).
IT8.7/1 and IT8.7/2 color scales for color calibration of input devices (scanners and digital cameras), IT8.7/1
The materials used in the IT8.7/2 color scale are color transparent positive and color photographic paper. IT8.7/1 is suitable for input color correction of transmissive scanners; IT8.7/2 is suitable for input color correction of reflective scanners.
The IT color scale consists of four parts:
1 sample color area. This part consists of 12 x 12 color blocks. According to the column, it is divided into dark toning blocks, intermediate toning blocks, and bright toning blocks, each of which has four saturation changes.
2 color ladders. There are seven columns in this section, three of which represent cyan, magenta, and yellow; the other three columns represent red, green, and blue; the middle column is neutral.
3 neutral gray ladder. At the bottom of the color scale is a twenty-two neutral neutral gray scale that varies by degree. Mainly used for basic correction of input devices.
4 optional areas. Different manufacturers can arrange three columns according to their own needs, such as feature colors. There are 286 color blocks on the entire color scale. These color patches are the standard color patches that create the scanner's ICC properties folder, which fully express the entire color gamut, and each color block contains a standard color data.
(2) Production of scanner ICC profile
The scanner ICC profile is created as follows:
1 The purpose of calibration calibration is to adjust equipment (such as scanners, monitors, printers, and printers) to a standard state to ensure that it meets production specifications. Most of the equipment is calibrated at the factory, but the quality of color reproduction is affected by factors such as environmental changes and equipment aging during use. Calibration is therefore important for reproducing colors. All equipment must be calibrated before it can be used.
After the scanner is turned on, it is warmed up, and then the scan driver software is run. First, the IT8 original is scanned, and the scanner's brightness, contrast, focal length, gray balance and midtone are corrected by the gray scale at the bottom of the IT original.
For example: to ensure that the gray ladder first level in the scanned image. The RGB value is maintained between 150 and 255. The RGB value of the 22nd level, that is, the dark adjustment part is maintained between 0 and 5. The RGB value of the eleventh stage of the middle part is 125 right.
If the R, G, and B values ​​of the scanned image are inconsistent, the scanner is color cast. It is assumed that the RGB value of the eleventh level of the intermediate adjustment is actually measured as R=118, G=125, and B=125. Increase the red intensity to balance with green and blue. This can ensure that the scanned image has a smaller color cast and a pure color.
2 Scan the IT8 color scale according to the reflection of the scanner; the transmission type selects the IT8.7/1 color standard or the IT8.7/2 color standard scan. In the scan menu, uncheck the net, sharpen, level adjustment and other options related to color management, and then save the scanned RGB image.
3 There are many softwares for generating ICC profile creation feature folders in ICC profile creation software, for example: Heidelberg software, Agfa software.
Run the ICC property file creation software, open the standard file containing the color block chromaticity data and the scanned image file in the software. The software compares and corrects the RGB data in the image file with the Lab color chromaticity data of the color block standard. Optimize to get the scanner's property file, and finally save the file to end the production of the input device ICC profile.
In this ICC profile, i' records the basic characteristics of the color reproduction of this scanner. Different scanners have different ICC profiles. It can be seen that the IT8 color scale acts as a ruler for measuring the accuracy of color in the process of making ICC profiles.
Production of output device ICC profile
(1) IT8.7/3 digital standard color standard If the ICC characteristic file of the output device is to be produced, the IT8.7/3 digital standard color standard (hereinafter referred to as the color standard) is indispensable. The IT8.7/3 color standard is an electronic file suitable for output devices that use CMYK four colors for color performance.
A total of 928 different color blocks are included in the IT8.7/3 color standard. The color data of these color blocks are all CMYK data, and the CMYK dot coverage of each color block is different. When different output devices output the IT8.7/3 color standard, the 928 colors printed represent the output device. Color performance. Devices with strong color performance can show subtle differences between the blocks; while devices with poor color performance have fewer differences between patches, and the small differences between the patches are unclear. The ability of the output device to reproduce the IT8.7/3 color scale represents the output accuracy of the device.
On the IT8.7/3 color scale, the following different types of areas are included:
1 dark toner block area.
2 overprint color block area (check ink overprint effect j
3 does not contain black saturated color block area.
4 contains 20% black saturated color block area.
5 Gray area consisting of CMY or CMYK (check gray balance).
6 solid color block color area (to check the density of the field).
7CMYK ladder (check the dot coverage).
(2) The production process of the output device ICC profile
Take the printing equipment as an example: Explain the production of the ICC profile of the output device.
1 Calibration Before the official printing of the IT8.7/3 color standard, the control device is used to calibrate the printing equipment, mainly referring to the solid density and dot coverage. The environment and production conditions of the printing press are required to be stable. For example, the solid density and dot coverage in official production must be consistent with the printing of the IT8.7/3 color standard. Only the ICC profile generated in this way can correctly reflect this. The color characteristics of the press.
2 Printing IT8.7/3 color standard will output the IT8.7/3 color standard and get proofs by printing. In addition, the film output and the printing process are adjusted to the standard state.
3 In the ICC profile creation software to generate ICC profile to run the ICC profile creation software, select the measurement options, generally online automatic measurement, the scanning spectrophotometer is driven, according to the prompts for color measurement of IT8.7/3 printed proofs After the measurement is finished, the software accurately compares the measured chromaticity data with the CMYK data of the color block in the color standard, and generates the ICC characteristic file of the output device by the software. Save this ICC profile.
Unlike a scanner that has only one ICC profile, a single press may have multiple ICC profiles because if the paper, ink, dot, and environmental conditions change, it will have an effect on color, so it must be Make multiple ICC profiles for different paper and ink combinations to meet your production needs.
If each device associated with color reproduction has an ICC profile, it provides the necessary foundation for color copy consistency. The following is only a screen soft proof to illustrate the importance of ICC profiles in color reproduction. A color job must be sampled before it is officially printed. One of the functions of proofing is to check the quality of the color on the sample. If the error can be found before the official printing, the cost can be reduced, and the preview can be previewed to the actual printing. What about the color effect?
The display is completely different from the mechanism for printing and reproducing colors. The red, green and blue colors are generated on the display screen, which are colored in the color-light mixing mode, and the yellow, magenta, cyan and black colors used in the four-color printing are four. The ink is colored in a color mixing mode; the color gamut of the two devices is also different. Therefore, the color seen on the display actually has a large difference from the color on the final print.
The basic principle of screen soft proofing:
Display - Display (ICC) - Color Management (CMM) - Printing Machine (ICC) Printing Machine
However, if there are ICC profiles for the display and printing equipment and the color conversion module (CMM), the color of the final print can be previewed in advance through the display. Since the ICC profile contains the characteristics of the device's reproduction color, the color management software will compare the ICC profile of the two devices to determine whether the color in the image file can be printed. If there is a super color gamut color, the color tube software will convert the super gamut color so that the final print color effect can be correctly previewed on the display.
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