The printing process is actually an image on the original document. In various types of print input/output devices, the original image information is transmitted, how to realize the maximum compatibility between the input and output devices, and the amount of input/output information from the original information. Sexuality and consistency, that is, to ensure the accuracy of information transmission as possible, to achieve faithful to the best copy of the original.
To print the manuscripts to be copied, the color separation must be carried out first. Now the color separation technology has evolved from the traditional photographic color separation and electronic color separation to the current desktop publishing system.
The color printing and printing process of the desktop publishing system is essentially the process of converting the color information of the original graphic and text through various devices and different color spaces so that the color can be restored. The color reproduction depends on the device that produced it, but in the integrated environment of the desktop publishing system, since each device has a different color gamut and color characteristics, the graphic color information is precisely controlled and transmitted in the desktop publishing system. It is particularly difficult. What you see is the ultimate goal of copying the original document. To achieve this goal, you must implement effective device-independent color management in the desktop publishing system to ensure the compatibility of input and output signals between devices, and to reduce and compensate for devices. The difference of color characteristics and the influence of different color modes on the color information, so that the color information of the graphic color data is transferred between different color spaces and devices having different color characteristics, and the color distortion is minimized so as to ensure that the color of the same picture is input. The effects shown in the display and then in the output are matched as much as possible, so that the reproduction and the original color are in harmony.
To do a good job in the color management of desktop publishing systems, the key is to handle the unified color space, device system characterization and color conversion and Other links.
First, to ensure the unification of color mode and color space In the desktop publishing system, color reproduction often involves three color modes of RGB, CMYK, and Lab. RGB is a color mode of color light. It consists of three channels: red, green and blue. In this mode, other colors are formed by the superposition of these three primary colors. Since all three colors have 256 luminance levels, three color overlays can create 16.7 million colors. In desktop publishing systems, the input and display devices such as scanners, digital cameras, and displays rely on this mode to express colors. When sunlight strikes an object, it absorbs some of the light and reflects it. Reflected light is the color of the object we see. This is a subtractive mode. Relying on this color reduction method, CMYK patterns suitable for printing and printing have evolved. Since in reality these three colors of ink are difficult to superimpose true black, black is introduced during printing and printing to enhance dark tone and darken the dark colors. Although the color defined by this color mode is much less than that defined by RGB, that is, the color space is much smaller, output devices such as imagesetter, printer, and proofer in the desktop color prepress system depend on this mode. To reproduce color. The Lab mode is a color model developed by the CIE (International Commission on Illumination). Any color in the natural world can be expressed in Lab space, and its color space is larger than RGB space. In addition, this model is a digital way to describe the human visual sense, and has nothing to do with the device, so it makes up for the lack of RGB and CMYK modes that must rely on the device's color characteristics.
Because Lab's color space is larger than the color space of RGB mode and CMYK mode. This means that the color information that RGB and CMYK can describe can be mapped in Lab space. Therefore, in the desktop publishing system's color management, if all color conversion and color correction jobs are based on Lab space, when color data is converted from Lab space to RGB or CMYK space, color data will not be caused due to insufficient data volume. deviation. From this we can see that in the color management, to make the color space can be unified, it should be based on this Lab-mode that is independent of the device and has a large color space.
In summary, in the prepress production process, we should store the color information obtained by scanners and digital cameras working in RGB mode in Lab mode, and perform color editing and correction in the Lab color space. When printing or filming, it is converted to CMYK space. This is the best solution for color processing. Because the printer and the photo-composing machine express colors in the CMYK mode, in practice, many operators are also accustomed to performing in the CMYK space when editing corrected colors. This is undesirable because it can cause color loss. Operating in CMYK can also slow down the calculation from the computer.
Second, the description of color characterization and system characterization of the device Desktop publishing system is an open system, each device can only reproduce or display a specific range of colors, such as scanners, monitors, Digital cameras generally use RGB space to express colors; color printers, proofers, and imagesetters generally use CMYK space to express colors. In addition, due to differences in the color characteristics of different devices, as well as the use of the environment and the state of the device, even the same device, its color characteristics are also relatively unstable. The result of color reproduction depends on the device that produced it. Without understanding the differences between each device, the transfer of color information is bound to be greatly affected, and the desired color cannot be obtained. The system characterization process of the device is essentially the formation of the color profile of different devices in the desktop publishing system, and the process of using the file to coordinate the entire desktop publishing system. In order to ensure the stability, reliability and continuity of the color information in the transmission process, the input, display and output devices must be systematically characterized to make the device in a standard state. Color management is to detect a device through a series of color measurement tools, and draw the device's chroma or color gamut characteristic curve, and then make a device's color description file against a device-independent color model. And these color description files are the mutual conversion credential between the color space of the respective device and the standard and device-independent color space, which ensures the stability of the color characteristics of the device itself. ICC developed a cross-platform and system ICC standard to enable the sharing of color information in multi-device environments. In this standard, they define the format and type of the device's color profile and define a virtual device-independent color space. Then according to this format, the original device color space is converted to a virtual space, and then the virtual space is converted to the target device color space, thereby ensuring the correct transfer of color information in the input and output devices.
Third, pay attention to the color space conversion and the choice of commonly used methods Color space conversion is the color image data with the device-independent color space for the bridge, the 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, since 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, so as to obtain a mixture of colors in 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 be coordinated and unified when transferring color information; in addition, the color space conversion should be selected 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.
To print the manuscripts to be copied, the color separation must be carried out first. Now the color separation technology has evolved from the traditional photographic color separation and electronic color separation to the current desktop publishing system.
The color printing and printing process of the desktop publishing system is essentially the process of converting the color information of the original graphic and text through various devices and different color spaces so that the color can be restored. The color reproduction depends on the device that produced it, but in the integrated environment of the desktop publishing system, since each device has a different color gamut and color characteristics, the graphic color information is precisely controlled and transmitted in the desktop publishing system. It is particularly difficult. What you see is the ultimate goal of copying the original document. To achieve this goal, you must implement effective device-independent color management in the desktop publishing system to ensure the compatibility of input and output signals between devices, and to reduce and compensate for devices. The difference of color characteristics and the influence of different color modes on the color information, so that the color information of the graphic color data is transferred between different color spaces and devices having different color characteristics, and the color distortion is minimized so as to ensure that the color of the same picture is input. The effects shown in the display and then in the output are matched as much as possible, so that the reproduction and the original color are in harmony.
To do a good job in the color management of desktop publishing systems, the key is to handle the unified color space, device system characterization and color conversion and Other links.
First, to ensure the unification of color mode and color space In the desktop publishing system, color reproduction often involves three color modes of RGB, CMYK, and Lab. RGB is a color mode of color light. It consists of three channels: red, green and blue. In this mode, other colors are formed by the superposition of these three primary colors. Since all three colors have 256 luminance levels, three color overlays can create 16.7 million colors. In desktop publishing systems, the input and display devices such as scanners, digital cameras, and displays rely on this mode to express colors. When sunlight strikes an object, it absorbs some of the light and reflects it. Reflected light is the color of the object we see. This is a subtractive mode. Relying on this color reduction method, CMYK patterns suitable for printing and printing have evolved. Since in reality these three colors of ink are difficult to superimpose true black, black is introduced during printing and printing to enhance dark tone and darken the dark colors. Although the color defined by this color mode is much less than that defined by RGB, that is, the color space is much smaller, output devices such as imagesetter, printer, and proofer in the desktop color prepress system depend on this mode. To reproduce color. The Lab mode is a color model developed by the CIE (International Commission on Illumination). Any color in the natural world can be expressed in Lab space, and its color space is larger than RGB space. In addition, this model is a digital way to describe the human visual sense, and has nothing to do with the device, so it makes up for the lack of RGB and CMYK modes that must rely on the device's color characteristics.
Because Lab's color space is larger than the color space of RGB mode and CMYK mode. This means that the color information that RGB and CMYK can describe can be mapped in Lab space. Therefore, in the desktop publishing system's color management, if all color conversion and color correction jobs are based on Lab space, when color data is converted from Lab space to RGB or CMYK space, color data will not be caused due to insufficient data volume. deviation. From this we can see that in the color management, to make the color space can be unified, it should be based on this Lab-mode that is independent of the device and has a large color space.
In summary, in the prepress production process, we should store the color information obtained by scanners and digital cameras working in RGB mode in Lab mode, and perform color editing and correction in the Lab color space. When printing or filming, it is converted to CMYK space. This is the best solution for color processing. Because the printer and the photo-composing machine express colors in the CMYK mode, in practice, many operators are also accustomed to performing in the CMYK space when editing corrected colors. This is undesirable because it can cause color loss. Operating in CMYK can also slow down the calculation from the computer.
Second, the description of color characterization and system characterization of the device Desktop publishing system is an open system, each device can only reproduce or display a specific range of colors, such as scanners, monitors, Digital cameras generally use RGB space to express colors; color printers, proofers, and imagesetters generally use CMYK space to express colors. In addition, due to differences in the color characteristics of different devices, as well as the use of the environment and the state of the device, even the same device, its color characteristics are also relatively unstable. The result of color reproduction depends on the device that produced it. Without understanding the differences between each device, the transfer of color information is bound to be greatly affected, and the desired color cannot be obtained. The system characterization process of the device is essentially the formation of the color profile of different devices in the desktop publishing system, and the process of using the file to coordinate the entire desktop publishing system. In order to ensure the stability, reliability and continuity of the color information in the transmission process, the input, display and output devices must be systematically characterized to make the device in a standard state. Color management is to detect a device through a series of color measurement tools, and draw the device's chroma or color gamut characteristic curve, and then make a device's color description file against a device-independent color model. And these color description files are the mutual conversion credential between the color space of the respective device and the standard and device-independent color space, which ensures the stability of the color characteristics of the device itself. ICC developed a cross-platform and system ICC standard to enable the sharing of color information in multi-device environments. In this standard, they define the format and type of the device's color profile and define a virtual device-independent color space. Then according to this format, the original device color space is converted to a virtual space, and then the virtual space is converted to the target device color space, thereby ensuring the correct transfer of color information in the input and output devices.
Third, pay attention to the color space conversion and the choice of commonly used methods Color space conversion is the color image data with the device-independent color space for the bridge, the 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, since 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, so as to obtain a mixture of colors in 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 be coordinated and unified when transferring color information; in addition, the color space conversion should be selected 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.
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