In order to produce the same color effect for all the equipment before printing, we need to establish a standard color management system. The key to color management is based on a standard color space, and uses this as a reference to perform color calibration on each device in the replication process, establish its color profile, and then use Profile to perform color conversion during color transfer. In order to ensure that the same screen color from the input, display, to the output (or network transmission) in the performance of the best match, and ultimately make the copy and the original color to achieve the same.
The implementation of color management
1. Matching a suitable color management system
The currently more mature color management systems are: Apple, ColorSync 2.0, 2.1 (CMS), Kodak Precision CMS (Kcms), Agfa Fototune Flow, Linocolor 5.0, 6.0, and the like. Users can choose the right color management system according to their own hardware and software system configuration.
Take Colorsync2.0CMS as an example, including:
1 Colorsync software: Colorsync, Colosync System Profile, ColorSyne Profile.
2 Profiles of different devices such as scanners, monitors, imagesetters, printers, etc.:
a. View open ICC, which is used to generate a profile file for the display, contains a set of View open ICC programs and a colorimeter to measure the screen color.
b. Scan open ICC, used for scanners to generate profile files, contains a set of Scan open ICC programs and three major manufacturers kodak Fuju Agfa's transmissive, reflective IT8 standard color code.
c. Print open ICC to generate a profile file for a color printer or a print process, including a Print open ICC program and a spectrophotometer.
3 Application software for implementing color management
Lincolor, version 4.1, 5.0, and 6.0: Linocolor is installed on the Macintosh and controls the scanner with a Mac CTU card. CTU is the abbreviation of Color Transform Unit. It is a color space conversion card, which enables fast conversion of color data between RGB, CMYK and CIE, Lab color space. The CTU card has a very high computational power, which enables a huge amount of color conversion operations to be completed instantaneously, and almost simultaneously scans the scanned image data from one color space to another color space to ensure high-quality color separation.
Therefore, in a broad sense, in addition to its core software, the color management system (CMS) should also include: ColorSync 2.0, 2.1, an operating system that supports color management; Profiles of devices; Application software that supports color management; All hardware devices in the process; Spectral measuring instruments; Color management process planning.
2. Establish a standard color environment
Observe the color can not be separated from the light source, in order to accurately distinguish the color, should use a standard light source, the standard light source has a standard color temperature, the current national and international regulations to observe the reflection sample using the light source color temperature of 5000K or 6500K; second is a higher significant The color index, which is usually a fluorescent tube with a color rendering index greater than 95%, must be transmitted through a standard light source for observation of a transmitted document so that it is consistent with the light source for viewing printed matter. Domestic and foreign regulations stipulate the use of a 5000K (D50) fluorescent tube.
3. Configure color measurement instruments and control tools
Image copying is a systematic project. Scanning color separation, screen display, output film, printing PS printing, proofing and printing from the originals all require quantification of color and precise data control to standardize the operation. This requires professional use. Color measurement instruments and tools to effectively detect and control the copy process, ensuring quality and stability. The following measuring instruments and control tools are indispensable: 1 Screen Calibrator: The sampler of the calibration instrument is attached to the screen to sample the screen. When the RGB tri-color ratio is unbalanced and color cast occurs, it can be performed by software. Adjust it to balance it. 2 Spectrophotometer: Color measurements are performed on 928 color samples in the IT8-7.3 standard color scale produced by the output device, and the results are compared with standard data to obtain new spectral information, thereby establishing the profile of the output device. 3 transmission densitometer. For the linearization of the laser imagesetter, one is to measure the maximum density value of the output film and the bottom ash value of the white film base; the other is to measure the network value from 2%, 50%, 98% at all levels to control the network points at all levels. The standard value reached. 4Reflectance Density Meter: It is used to measure the density value, dot gain, trap rate and relative contrast of four-color inks to control and stabilize the quality of proofing and printing. 5 Bruner control strip: It is used to measure and control the technical parameters of proofing and printing density values, dot gain, etc. It is generally used to lengthen 85 type control strips. 5 print control bar: used to monitor the exposure and development time of the printing plate, currently widely used at home and abroad VGRA control bar. 7 Gray scales and color scales: Monitors the gray balance and color correction for film and color samples.
4. Ensure that the colors between input, display, and output are accurate and stable
The focus of color management. The first is to characterize the scanner management, make the scanning technology more standardized, more accurate color reproduction; second is to make all kinds of production software on the monitor display image color and digital proofer output sample color close, and then with The prints are similar in color. Therefore, corrections and descriptions of displays, scanners, and printers are of utmost importance.
1) Display Correction and Description
At present, the desktop system uses the monitor as a pre-proofing method and relies on the screen color to adjust the image color. Therefore, one of the keys to the color management system is to realize the display effect of the display is close to the output proofing or printing effect.
1 Display itself correction: The display has been calibrated at the factory, but it still needs to be corrected frequently with time, changes in the use of the environment and other reasons. Variables that the monitor needs to correct include brightness, gamma, color temperature, and more.
a. Determine the color temperature: In order to make the color of the image seen by the operator on the screen as close to the color of the image output on the paper as possible in the prepress system, the color temperature of the display is required to be 5000K-6500K, and the default value of the Mac is 6500K. The color temperature reflects the color balance of the white area on the screen (cold and warm), the color temperature is low, the screen color is yellow, and the high color temperature is blue.
b. Determine the gamma value: This value affects the distribution of highlights and shadows in the image. When there is no color management system, the gamma can be adjusted by comparing the final print of the same document with the screen image to make them similar. When using a color management system, the system sets a typical gamma value, such as EFI's RGB calibration standard that specifies a display gamma of 2.20, and a Mac setting of 1.8. The actual production should focus on correcting the monitor for the two or three workstations used for scanning color separations and adjustments.
2 screen tone school: a. Under the observation conditions specified in ISO 3664, the screen colors are adjusted with IT8 color scales to simulate proofing or printing effects. b. Use the IT8 color standard, output the film, and play standard color proofs. c. Use the II8 color standard in the screen of the IT8 color standard sample that is displayed to adjust. d. Add a black mask on the top and left side of the screen to prevent interference from ambient light and make the observed screen color more accurate. e. At present, the screen cannot fully simulate the ink proofing and printing effects, but it can be used as a reference for the pre- proofing color, and rely on the dot value of the CMYK four-color ink displayed by the color separation film to make an accurate adjustment.
2) Scanner Calibration and Profile Creation
The scanner plays a crucial role in realistically reproducing the color gradation in the image art. Therefore, the characteristic management of the scanner is the most important, and now some high-end professional platform scanners have developed a color management system with its own characteristics.
1 Scanner Calibration: The scanner calibration variables are brightness, contrast, and color temperature. The focus is on the correction of the standard white, so that the RGB three-channel signal is the same, to ensure the accuracy of the input system color;
2 Create Profile: By testing the color performance of the scanner, establish a standard ICC Profile, Colorsync is used to convert the color of the scanner file.
a. Because the sensitivity of the CCD optocoupler of the platform scanner and the change of the color temperature of the light source with time and other factors will be reduced, after the equipment is used for a period of time, a standardized test shall be made and a new profile shall be re-established so as to guarantee the file's Correctness.
b. Since the printability of printing inks and papers used in actual production is not stable, the printability of inks, papers, etc. used on the basis of the new profile should be based on the newly-created profile, and the neutral gray, level curve, and color should be further developed. Correct adjustments and other parameters make precise adjustments so that excellent image files are scanned.
c. Due to different types and contents of originals, different data settings should be made. We have established 5 sets of scanning parameters according to the manuscript: transmissive/reflective/printed/Chinese painting RGB/color edition, four-color black and white; each set contains 4 main contents: Neutral gray balance data, standard level curve, standard color amount, standard definition adjustment. In this way, the maximum amount of information can be captured directly from the manuscript and integrated with the color management system to give full play to the scanner's function to ensure accurate reproduction of most manuscript colors. However, for many current non-compliant manuscripts, it is necessary to restore originals. Based on the original, the original defects are adjusted and processed; at the same time, different parameters need to be set due to the different types of originals. Therefore, the best method at present is to use a color management system to set different scanning color separation parameters for different kinds of originals.
3) Correction and description of proofer and printer The role of the color print sheet is:
a. As the basis for adjusting the colors of screens, scanners, and digital printers, match them with their Profile;
b. Printers use print quality control such as ink density, gray balance, and color saturation. To output accurate color proofs, one must adjust the proofer and printer; the second is to establish a proofing profile, and there must be multiple characteristics to describe the color characteristics and color gamut of various combinations of paper and ink. .
Application of color management
The company where the author is located purchased an EPSONPRO color inkjet printer in 2000, and also purchased Founder Century RIP software and its plug-in CMS. Here's how we use this color management software:
PSPNT2.1 provides an ICCColor.TIF file, which is a set of ICC-compliant color patches suitable for X-Rite DTP41 colorimeter measurements. It contains 928 CMYK color blocks. The output device outputs the color blocks, using Kodak Color. The Flow tool can generate the device's standard ICC profile file, select the ICC profile in the PSPNT, and use the CMS for accurate color output. If ink or paper is replaced, new ink or paper needs to be re-outputted and measured to generate a new ICC Profile.
1. Generate ICC color patches for the printing environment
1 Output the ICCColor.TIF file with the same parameters as normal production. This file can be output using the same parameter template as normal production. 2 Printed in accordance with the normal production process, you can get color samples.
2. Generate ICC patch scripts for the print environment
Printers, especially inkjet printers, often have very high ink diffusion. Therefore, if you do not adjust them, the color of the output color will be very deep, affecting the accuracy of color patches reflecting the color characteristics of the printer. Therefore, the following steps should be taken for the ICC patch sample generated by the printer: 1 Adjust the grayscale conversion curve of the PSPNT to ensure that the CMYK four-color 21st-level ash ladder has the correct density. It is necessary to ensure the density of ash ladders at all levels while ensuring that the solid colors have sufficient saturation. The method: First, PSPNT with some grayscale conversion curve, in the PSPNT installation directory Color subdirectory, these curves can be used as the starting curve of the calibration; Second, the color of the print and the printer's own drive to play the color The block is compared as far as possible with its density. 2 Use calibrated curves to print ICCColo
The implementation of color management
1. Matching a suitable color management system
The currently more mature color management systems are: Apple, ColorSync 2.0, 2.1 (CMS), Kodak Precision CMS (Kcms), Agfa Fototune Flow, Linocolor 5.0, 6.0, and the like. Users can choose the right color management system according to their own hardware and software system configuration.
Take Colorsync2.0CMS as an example, including:
1 Colorsync software: Colorsync, Colosync System Profile, ColorSyne Profile.
2 Profiles of different devices such as scanners, monitors, imagesetters, printers, etc.:
a. View open ICC, which is used to generate a profile file for the display, contains a set of View open ICC programs and a colorimeter to measure the screen color.
b. Scan open ICC, used for scanners to generate profile files, contains a set of Scan open ICC programs and three major manufacturers kodak Fuju Agfa's transmissive, reflective IT8 standard color code.
c. Print open ICC to generate a profile file for a color printer or a print process, including a Print open ICC program and a spectrophotometer.
3 Application software for implementing color management
Lincolor, version 4.1, 5.0, and 6.0: Linocolor is installed on the Macintosh and controls the scanner with a Mac CTU card. CTU is the abbreviation of Color Transform Unit. It is a color space conversion card, which enables fast conversion of color data between RGB, CMYK and CIE, Lab color space. The CTU card has a very high computational power, which enables a huge amount of color conversion operations to be completed instantaneously, and almost simultaneously scans the scanned image data from one color space to another color space to ensure high-quality color separation.
Therefore, in a broad sense, in addition to its core software, the color management system (CMS) should also include: ColorSync 2.0, 2.1, an operating system that supports color management; Profiles of devices; Application software that supports color management; All hardware devices in the process; Spectral measuring instruments; Color management process planning.
2. Establish a standard color environment
Observe the color can not be separated from the light source, in order to accurately distinguish the color, should use a standard light source, the standard light source has a standard color temperature, the current national and international regulations to observe the reflection sample using the light source color temperature of 5000K or 6500K; second is a higher significant The color index, which is usually a fluorescent tube with a color rendering index greater than 95%, must be transmitted through a standard light source for observation of a transmitted document so that it is consistent with the light source for viewing printed matter. Domestic and foreign regulations stipulate the use of a 5000K (D50) fluorescent tube.
3. Configure color measurement instruments and control tools
Image copying is a systematic project. Scanning color separation, screen display, output film, printing PS printing, proofing and printing from the originals all require quantification of color and precise data control to standardize the operation. This requires professional use. Color measurement instruments and tools to effectively detect and control the copy process, ensuring quality and stability. The following measuring instruments and control tools are indispensable: 1 Screen Calibrator: The sampler of the calibration instrument is attached to the screen to sample the screen. When the RGB tri-color ratio is unbalanced and color cast occurs, it can be performed by software. Adjust it to balance it. 2 Spectrophotometer: Color measurements are performed on 928 color samples in the IT8-7.3 standard color scale produced by the output device, and the results are compared with standard data to obtain new spectral information, thereby establishing the profile of the output device. 3 transmission densitometer. For the linearization of the laser imagesetter, one is to measure the maximum density value of the output film and the bottom ash value of the white film base; the other is to measure the network value from 2%, 50%, 98% at all levels to control the network points at all levels. The standard value reached. 4Reflectance Density Meter: It is used to measure the density value, dot gain, trap rate and relative contrast of four-color inks to control and stabilize the quality of proofing and printing. 5 Bruner control strip: It is used to measure and control the technical parameters of proofing and printing density values, dot gain, etc. It is generally used to lengthen 85 type control strips. 5 print control bar: used to monitor the exposure and development time of the printing plate, currently widely used at home and abroad VGRA control bar. 7 Gray scales and color scales: Monitors the gray balance and color correction for film and color samples.
4. Ensure that the colors between input, display, and output are accurate and stable
The focus of color management. The first is to characterize the scanner management, make the scanning technology more standardized, more accurate color reproduction; second is to make all kinds of production software on the monitor display image color and digital proofer output sample color close, and then with The prints are similar in color. Therefore, corrections and descriptions of displays, scanners, and printers are of utmost importance.
1) Display Correction and Description
At present, the desktop system uses the monitor as a pre-proofing method and relies on the screen color to adjust the image color. Therefore, one of the keys to the color management system is to realize the display effect of the display is close to the output proofing or printing effect.
1 Display itself correction: The display has been calibrated at the factory, but it still needs to be corrected frequently with time, changes in the use of the environment and other reasons. Variables that the monitor needs to correct include brightness, gamma, color temperature, and more.
a. Determine the color temperature: In order to make the color of the image seen by the operator on the screen as close to the color of the image output on the paper as possible in the prepress system, the color temperature of the display is required to be 5000K-6500K, and the default value of the Mac is 6500K. The color temperature reflects the color balance of the white area on the screen (cold and warm), the color temperature is low, the screen color is yellow, and the high color temperature is blue.
b. Determine the gamma value: This value affects the distribution of highlights and shadows in the image. When there is no color management system, the gamma can be adjusted by comparing the final print of the same document with the screen image to make them similar. When using a color management system, the system sets a typical gamma value, such as EFI's RGB calibration standard that specifies a display gamma of 2.20, and a Mac setting of 1.8. The actual production should focus on correcting the monitor for the two or three workstations used for scanning color separations and adjustments.
2 screen tone school: a. Under the observation conditions specified in ISO 3664, the screen colors are adjusted with IT8 color scales to simulate proofing or printing effects. b. Use the IT8 color standard, output the film, and play standard color proofs. c. Use the II8 color standard in the screen of the IT8 color standard sample that is displayed to adjust. d. Add a black mask on the top and left side of the screen to prevent interference from ambient light and make the observed screen color more accurate. e. At present, the screen cannot fully simulate the ink proofing and printing effects, but it can be used as a reference for the pre- proofing color, and rely on the dot value of the CMYK four-color ink displayed by the color separation film to make an accurate adjustment.
2) Scanner Calibration and Profile Creation
The scanner plays a crucial role in realistically reproducing the color gradation in the image art. Therefore, the characteristic management of the scanner is the most important, and now some high-end professional platform scanners have developed a color management system with its own characteristics.
1 Scanner Calibration: The scanner calibration variables are brightness, contrast, and color temperature. The focus is on the correction of the standard white, so that the RGB three-channel signal is the same, to ensure the accuracy of the input system color;
2 Create Profile: By testing the color performance of the scanner, establish a standard ICC Profile, Colorsync is used to convert the color of the scanner file.
a. Because the sensitivity of the CCD optocoupler of the platform scanner and the change of the color temperature of the light source with time and other factors will be reduced, after the equipment is used for a period of time, a standardized test shall be made and a new profile shall be re-established so as to guarantee the file's Correctness.
b. Since the printability of printing inks and papers used in actual production is not stable, the printability of inks, papers, etc. used on the basis of the new profile should be based on the newly-created profile, and the neutral gray, level curve, and color should be further developed. Correct adjustments and other parameters make precise adjustments so that excellent image files are scanned.
c. Due to different types and contents of originals, different data settings should be made. We have established 5 sets of scanning parameters according to the manuscript: transmissive/reflective/printed/Chinese painting RGB/color edition, four-color black and white; each set contains 4 main contents: Neutral gray balance data, standard level curve, standard color amount, standard definition adjustment. In this way, the maximum amount of information can be captured directly from the manuscript and integrated with the color management system to give full play to the scanner's function to ensure accurate reproduction of most manuscript colors. However, for many current non-compliant manuscripts, it is necessary to restore originals. Based on the original, the original defects are adjusted and processed; at the same time, different parameters need to be set due to the different types of originals. Therefore, the best method at present is to use a color management system to set different scanning color separation parameters for different kinds of originals.
3) Correction and description of proofer and printer The role of the color print sheet is:
a. As the basis for adjusting the colors of screens, scanners, and digital printers, match them with their Profile;
b. Printers use print quality control such as ink density, gray balance, and color saturation. To output accurate color proofs, one must adjust the proofer and printer; the second is to establish a proofing profile, and there must be multiple characteristics to describe the color characteristics and color gamut of various combinations of paper and ink. .
Application of color management
The company where the author is located purchased an EPSONPRO color inkjet printer in 2000, and also purchased Founder Century RIP software and its plug-in CMS. Here's how we use this color management software:
PSPNT2.1 provides an ICCColor.TIF file, which is a set of ICC-compliant color patches suitable for X-Rite DTP41 colorimeter measurements. It contains 928 CMYK color blocks. The output device outputs the color blocks, using Kodak Color. The Flow tool can generate the device's standard ICC profile file, select the ICC profile in the PSPNT, and use the CMS for accurate color output. If ink or paper is replaced, new ink or paper needs to be re-outputted and measured to generate a new ICC Profile.
1. Generate ICC color patches for the printing environment
1 Output the ICCColor.TIF file with the same parameters as normal production. This file can be output using the same parameter template as normal production. 2 Printed in accordance with the normal production process, you can get color samples.
2. Generate ICC patch scripts for the print environment
Printers, especially inkjet printers, often have very high ink diffusion. Therefore, if you do not adjust them, the color of the output color will be very deep, affecting the accuracy of color patches reflecting the color characteristics of the printer. Therefore, the following steps should be taken for the ICC patch sample generated by the printer: 1 Adjust the grayscale conversion curve of the PSPNT to ensure that the CMYK four-color 21st-level ash ladder has the correct density. It is necessary to ensure the density of ash ladders at all levels while ensuring that the solid colors have sufficient saturation. The method: First, PSPNT with some grayscale conversion curve, in the PSPNT installation directory Color subdirectory, these curves can be used as the starting curve of the calibration; Second, the color of the print and the printer's own drive to play the color The block is compared as far as possible with its density. 2 Use calibrated curves to print ICCColo
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