For a long time, the separation and printing method used in printing and printing is different. From a craft point of view, printing is to synthesize a color picture with four colors of cyan (C), magenta (M), yellow (Y), and black (K); printing and dyeing is to represent each spot color separately The representative color. Since printing has many common features with printing and dyeing processes, coupled with the widespread use of prepress processing systems, people are trying to use computer color separation process to find different ways to apply four-color printing to printing and color separation and plate making.
Printing and dyeing products give us the impression that there are too many mud spots on the prints, the screen is too dark, and the colors are distorted. The main reason is the direct application of the printing process and parameters, resulting in the expansion of the actual layout of the Internet site is too large. In this regard, I would like to understand some of the trials of printing methods used for printing and dyeing in the following three aspects.
The computer is used for printing plate separation, the image processing is mainly the use of Photoshop image color separation software, it needs to change the PrintingInksSetup in the File/Preferences item of the working menu for different printing inks, printing media, printing process; SeparationSetup The two subitems, the work that can't be done for Photoshop graphics software, are done by special items in the RIP interpreter. The implementation plan is as follows:
First, ink settings. Change the hue of the image produced on the screen by printing the ink set so that it is as consistent as possible with the dye-printed sample.
Second, the color separation settings, by adjusting the image RGB color mode to CMYK color mode curve, to meet the printing and dyeing process requirements.
Third, RIP compensation. The main compensation was established because the settings in Photoshop did not meet the printing and dyeing process requirements.
1 printing ink settings
The printing ink setting is set for the medium (satin) and dye of the printing product, so that the screen sees and the tone obtained by the sample remains the same.
We understand the requirements for printing and dyeing from the following parameters:
1.1 Ink setting
Swop (coated) is usually used for printing. This is a standard printing method for American web offset printing. The chromaticity coordinates and brightness factor of the ink can be easily obtained from related materials. The x and y coordinates of the color can be found from the chromaticity coordinates, and the brightness factor Y is measured upwards at the white point.
If the printing ink CMYK chromaticity coordinates and brightness factors and printing materials CMYK value is different, this will lead to screen color and print color difference. In this regard, the following two methods can be used.
(1) Select an ink parameter in the ink setting item for printing and dyeing. If the color difference of the sample is small, the dye can be corrected when preparing the dye. For the chromaticity coordinates and brightness factors of printing and dyeing materials are unfamiliar, from the perspective of choosing the printing media similar to the printing and dyeing media, it is recommended to select an ink for the Swop (NewPrint) method. The main concern is that newsprint has similar water absorption and silk properties.
(2) If the difference in color difference is too large with the above method, use this scheme: In the InksColors item, select Other, and fill in the Custon column with the chromaticity coordinates and brightness factors of the actual printing dye. The specific operation can be used tedtprint file in Photoshop (Calibrat sub-category in Photo-shop) output film, and then printed on the silk samples, and then use the color separation instrument can measure the reflectance curve of each spectrum and calculate x, Y, z Value, fill the value into the Custom column.
1.2 point gain
Bleeding and diffusion occur when dyes are printed on silk. This phenomenon cannot be avoided. Since the enlargement of the printed dots has a greater influence on the midtones and shadow tone areas, the enlargement rate of the dots is different for different fabrics. If the print point is enlarged, the image becomes darker. From the existing samples, the image on the sample is significantly darker, which means that the original print point gain of 20% is not enough to compensate for the actual point expansion rate. In Photoshop, the point gain can be up to 40% (relative increment in 50% grayscale), so the point gain can be selected to be about 35%.
1.3 Gray balance
Usually the image we see on the display has some differences in lightness and darkness compared to the dyed samples, and some of the colors also have large differences. For minimum requirements, at least lightness and darkness are as consistent as possible. If the sample is darker than the display image, the CMYK value in GrayBalance can be reduced, and vice versa (in the case of fixed point gain). Secondly, if the middle tone is a bit of a color cast, you need to move the gray output slider in Images/Adjust/Lev-els to control it, and count this r value in the Gray Balance column.
The above three parameters are useful when converting RGB mode to CMYK color mode in Photoshop. The change of parameters does not affect the RGB image display, only changing the display image of the CMYK mode on the screen without changing the data of the CMYK mode. That is, seeing the screen on the screen is darker, the screen can be brightened by changing the point gain and the gray balance, while the CMYK value remains unchanged. If this is done by adjusting the Image&/Adjust/Levels value to brighten the picture, the CMYK value will change.
2 separation settings
Scanned images are generally RGB color mode, when it is converted to CMYK mode, it needs to follow a certain conversion rules, that is to say there needs to be a group of color rules.
2.1 Separation type
In the printing industry, color separation processes using “gray components instead of GCR†or “background color removal†UCR are commonly used.
(1) GCR is also called "non-color structure" process. That is, the non-colored components in the picture (composed of complex colors) are all printed by black ink. For monochrome and inter-color, it does not work. People call the black edition a "long version."
Due to the blackness of black ink is not enough today, the density in the dark part of the image is low. This requires the use of colored inks in the dark areas of the non-colored components. This process is called "Background Gain" (UCA).
With the GCR method, the amount of the ink to be replaced by the complex color, dark color, and neutral gray ink is less affected, while the screen composed of the primary color and the question color locally is affected by the fluctuation of the ink amount to cause color cast. Therefore, when using the GCR method, the process requirements are relatively high.
(2) UCR is also called "color structure" process. The non-color and color components in the picture are all composed of YMC three primary colors. Since the achromatic components of the three primary colors are not sufficiently black, the amount of black ink is increased in the dark portion, and the amount of ink in the three primary colors is reduced at the same time. People often refer to black editions as "short-version" or "contour."
To sum up the two color separation methods, from the printing and dyeing process point of view, the use of UCR mode is better than GCR mode. This is mainly to reduce the unevenness in the process of making screen plate, and the unevenness of the amount of dye in the process of printing and dyeing. In terms of color effects, GCR is more delicate than UCR, so GCR is better when the process is relatively secure. In addition, GCR is usually used for coated materials, the dye dip is relatively small. UCR is used for non-coating materials (printing fabrics mostly belong to this category). In this way, different separation methods should be selected for different fabrics.
Under normal circumstances, the screens produced by UCR and GCR are unrecognizable to the naked eye. At the beginning of the trial, it is recommended to use UCR mode test to obtain other process parameters.
2.2 Black synthesis
This item is only valid for GCR mode. Since the GCR method replaces one or all of the C, M, and Y colors with black, the degree of substitution is selected by the item. From the printing point of view, Medium (medium) is preferred. For printing and dyeing, when the black is larger (the Heavy item), the C, M, and Y colors will be reduced, and it will show a softer effect, which is beneficial to the clarity of the picture.
2.3 Black ink limit
Control the total amount of black ink. For printing, the use of 90% to 100%; for printing and dyeing is less than the print parameters (such as 70% to 80%). If you find that the selected black ink is too much, you can drop a little black ink limit value.
2.4 Ink Total Limit
The total amount of ink indicates the total amount of C, M, Y, and K. If the ink has a limit, the remaining value is the total amount of oil for C, M, and Y. The value of c, M, Y and K in printing is generally not less than 300%, and for printing and dyeing, it is suitable between 250% and 300%. Because the amount of ink absorbed by printed silk is greater than the amount of ink absorbed by printed paper, the total amount of ink can be set lower for printing and dyeing.
2.5 additional amount of background
For the GCR method, black ink can not meet the dark part of the image alone (black ink purity is not enough), then it must be in the dark part of the image of non-color components, add color ink to set off. It only works on complex colors and does not work on primary colors or inter-colors. For printing, this item is generally not used, so it is not necessarily used for printing and dyeing.
3 Compensate printing and dyeing process in RIP software
Although the image seen on the screen has achieved satisfactory results, the actual sample is not satisfactory. In addition to some of the above parameters to meet the printing and dyeing process as much as possible, in addition, the linearity of the film when the film is released, the expansion rate of the dot screen when making the screen, and the tension when printing and dyeing, etc., will cause changes in the printing point, so it is necessary to make up. There are actually many ways to compensate. The commonly used method is: First pass the test to measure the dot enlargement rate of each step on the actual sample, and then add a bit of gain in the aforementioned Photoshop software, and also make up a bit when RIP rastering, making the actual sample on the three The stimulus value is as consistent as possible on the screen. Therefore, in order to obtain the correct printing and dyeing parameters, the following steps should be started:
(1) Adjust the focus of the photo-setter so as to reduce the expansion or contraction of the photo-setter's light spot, affecting the expansion rate of the film's Internet point and the appearance of interference fringes.
(2) adjust the film linearity. Different films have different characteristics such as development and fixing, so that the same size of light spot will have different size on the film. In order to compensate for the enlargement rate of each order in the film, it is necessary to compensate parameters in RIP.
(3) Compensation for network expansion in the printing process. In the previous description, we have defined a point expansion of 35% to 40%, which is only to compensate 50% of the tone. The compensation for each point is determined by Photoshop's default compensation curve. That is to say, this kind of compensation and reality have a certain amount of people. In addition, if the actual expansion rate of the 50% tone is 40%, then photoshop will be powerless. At this time we can only make one more compensation in the RIP.
Another method is that in Photoshop, the defined point gain is 0, and the dot expansion of each tone is compensated in RIP. The compensation value is the difference between the measured value and the set value of the sample.
(4) RIP parameter selection. For printing requirements, each color requirement can represent 0-255 levels, printing and dyeing do not have such a high requirement, generally can be controlled between 64 and 128 levels. Screening number: For the printing and dyeing requirements, the screen mesh number is between 98 and 118/cm. For the printing and dyeing process, the mesh number is between 24 and 39 [~/cm can meet the requirements. In order to meet a certain number of tones, an output of up to 60 mesh/inch screens with 600dpi photo output can reach up to 101 levels.
Screen angle: It is recommended that the screen angles of C, M, Y, and K color versions be l5. 75. 90. 45. . If there is a conflict between the silk screen pattern and the color pattern, you may choose to adjust the screen angle and the number of meshes (in general, the number of meshes should not change).
It can be seen from the above analysis that the color separation setting is related to the printing and dyeing process. In order to make the printing and dyeing effect close to the printing effect, when using Photoshop's color separation settings, we can make appropriate choices in its parameters to meet the printing and dyeing process requirements, supplemented with RIP compensation, and then look at the sample effect. Get experience and data.
Printing and dyeing products give us the impression that there are too many mud spots on the prints, the screen is too dark, and the colors are distorted. The main reason is the direct application of the printing process and parameters, resulting in the expansion of the actual layout of the Internet site is too large. In this regard, I would like to understand some of the trials of printing methods used for printing and dyeing in the following three aspects.
The computer is used for printing plate separation, the image processing is mainly the use of Photoshop image color separation software, it needs to change the PrintingInksSetup in the File/Preferences item of the working menu for different printing inks, printing media, printing process; SeparationSetup The two subitems, the work that can't be done for Photoshop graphics software, are done by special items in the RIP interpreter. The implementation plan is as follows:
First, ink settings. Change the hue of the image produced on the screen by printing the ink set so that it is as consistent as possible with the dye-printed sample.
Second, the color separation settings, by adjusting the image RGB color mode to CMYK color mode curve, to meet the printing and dyeing process requirements.
Third, RIP compensation. The main compensation was established because the settings in Photoshop did not meet the printing and dyeing process requirements.
1 printing ink settings
The printing ink setting is set for the medium (satin) and dye of the printing product, so that the screen sees and the tone obtained by the sample remains the same.
We understand the requirements for printing and dyeing from the following parameters:
1.1 Ink setting
Swop (coated) is usually used for printing. This is a standard printing method for American web offset printing. The chromaticity coordinates and brightness factor of the ink can be easily obtained from related materials. The x and y coordinates of the color can be found from the chromaticity coordinates, and the brightness factor Y is measured upwards at the white point.
If the printing ink CMYK chromaticity coordinates and brightness factors and printing materials CMYK value is different, this will lead to screen color and print color difference. In this regard, the following two methods can be used.
(1) Select an ink parameter in the ink setting item for printing and dyeing. If the color difference of the sample is small, the dye can be corrected when preparing the dye. For the chromaticity coordinates and brightness factors of printing and dyeing materials are unfamiliar, from the perspective of choosing the printing media similar to the printing and dyeing media, it is recommended to select an ink for the Swop (NewPrint) method. The main concern is that newsprint has similar water absorption and silk properties.
(2) If the difference in color difference is too large with the above method, use this scheme: In the InksColors item, select Other, and fill in the Custon column with the chromaticity coordinates and brightness factors of the actual printing dye. The specific operation can be used tedtprint file in Photoshop (Calibrat sub-category in Photo-shop) output film, and then printed on the silk samples, and then use the color separation instrument can measure the reflectance curve of each spectrum and calculate x, Y, z Value, fill the value into the Custom column.
1.2 point gain
Bleeding and diffusion occur when dyes are printed on silk. This phenomenon cannot be avoided. Since the enlargement of the printed dots has a greater influence on the midtones and shadow tone areas, the enlargement rate of the dots is different for different fabrics. If the print point is enlarged, the image becomes darker. From the existing samples, the image on the sample is significantly darker, which means that the original print point gain of 20% is not enough to compensate for the actual point expansion rate. In Photoshop, the point gain can be up to 40% (relative increment in 50% grayscale), so the point gain can be selected to be about 35%.
1.3 Gray balance
Usually the image we see on the display has some differences in lightness and darkness compared to the dyed samples, and some of the colors also have large differences. For minimum requirements, at least lightness and darkness are as consistent as possible. If the sample is darker than the display image, the CMYK value in GrayBalance can be reduced, and vice versa (in the case of fixed point gain). Secondly, if the middle tone is a bit of a color cast, you need to move the gray output slider in Images/Adjust/Lev-els to control it, and count this r value in the Gray Balance column.
The above three parameters are useful when converting RGB mode to CMYK color mode in Photoshop. The change of parameters does not affect the RGB image display, only changing the display image of the CMYK mode on the screen without changing the data of the CMYK mode. That is, seeing the screen on the screen is darker, the screen can be brightened by changing the point gain and the gray balance, while the CMYK value remains unchanged. If this is done by adjusting the Image&/Adjust/Levels value to brighten the picture, the CMYK value will change.
2 separation settings
Scanned images are generally RGB color mode, when it is converted to CMYK mode, it needs to follow a certain conversion rules, that is to say there needs to be a group of color rules.
2.1 Separation type
In the printing industry, color separation processes using “gray components instead of GCR†or “background color removal†UCR are commonly used.
(1) GCR is also called "non-color structure" process. That is, the non-colored components in the picture (composed of complex colors) are all printed by black ink. For monochrome and inter-color, it does not work. People call the black edition a "long version."
Due to the blackness of black ink is not enough today, the density in the dark part of the image is low. This requires the use of colored inks in the dark areas of the non-colored components. This process is called "Background Gain" (UCA).
With the GCR method, the amount of the ink to be replaced by the complex color, dark color, and neutral gray ink is less affected, while the screen composed of the primary color and the question color locally is affected by the fluctuation of the ink amount to cause color cast. Therefore, when using the GCR method, the process requirements are relatively high.
(2) UCR is also called "color structure" process. The non-color and color components in the picture are all composed of YMC three primary colors. Since the achromatic components of the three primary colors are not sufficiently black, the amount of black ink is increased in the dark portion, and the amount of ink in the three primary colors is reduced at the same time. People often refer to black editions as "short-version" or "contour."
To sum up the two color separation methods, from the printing and dyeing process point of view, the use of UCR mode is better than GCR mode. This is mainly to reduce the unevenness in the process of making screen plate, and the unevenness of the amount of dye in the process of printing and dyeing. In terms of color effects, GCR is more delicate than UCR, so GCR is better when the process is relatively secure. In addition, GCR is usually used for coated materials, the dye dip is relatively small. UCR is used for non-coating materials (printing fabrics mostly belong to this category). In this way, different separation methods should be selected for different fabrics.
Under normal circumstances, the screens produced by UCR and GCR are unrecognizable to the naked eye. At the beginning of the trial, it is recommended to use UCR mode test to obtain other process parameters.
2.2 Black synthesis
This item is only valid for GCR mode. Since the GCR method replaces one or all of the C, M, and Y colors with black, the degree of substitution is selected by the item. From the printing point of view, Medium (medium) is preferred. For printing and dyeing, when the black is larger (the Heavy item), the C, M, and Y colors will be reduced, and it will show a softer effect, which is beneficial to the clarity of the picture.
2.3 Black ink limit
Control the total amount of black ink. For printing, the use of 90% to 100%; for printing and dyeing is less than the print parameters (such as 70% to 80%). If you find that the selected black ink is too much, you can drop a little black ink limit value.
2.4 Ink Total Limit
The total amount of ink indicates the total amount of C, M, Y, and K. If the ink has a limit, the remaining value is the total amount of oil for C, M, and Y. The value of c, M, Y and K in printing is generally not less than 300%, and for printing and dyeing, it is suitable between 250% and 300%. Because the amount of ink absorbed by printed silk is greater than the amount of ink absorbed by printed paper, the total amount of ink can be set lower for printing and dyeing.
2.5 additional amount of background
For the GCR method, black ink can not meet the dark part of the image alone (black ink purity is not enough), then it must be in the dark part of the image of non-color components, add color ink to set off. It only works on complex colors and does not work on primary colors or inter-colors. For printing, this item is generally not used, so it is not necessarily used for printing and dyeing.
3 Compensate printing and dyeing process in RIP software
Although the image seen on the screen has achieved satisfactory results, the actual sample is not satisfactory. In addition to some of the above parameters to meet the printing and dyeing process as much as possible, in addition, the linearity of the film when the film is released, the expansion rate of the dot screen when making the screen, and the tension when printing and dyeing, etc., will cause changes in the printing point, so it is necessary to make up. There are actually many ways to compensate. The commonly used method is: First pass the test to measure the dot enlargement rate of each step on the actual sample, and then add a bit of gain in the aforementioned Photoshop software, and also make up a bit when RIP rastering, making the actual sample on the three The stimulus value is as consistent as possible on the screen. Therefore, in order to obtain the correct printing and dyeing parameters, the following steps should be started:
(1) Adjust the focus of the photo-setter so as to reduce the expansion or contraction of the photo-setter's light spot, affecting the expansion rate of the film's Internet point and the appearance of interference fringes.
(2) adjust the film linearity. Different films have different characteristics such as development and fixing, so that the same size of light spot will have different size on the film. In order to compensate for the enlargement rate of each order in the film, it is necessary to compensate parameters in RIP.
(3) Compensation for network expansion in the printing process. In the previous description, we have defined a point expansion of 35% to 40%, which is only to compensate 50% of the tone. The compensation for each point is determined by Photoshop's default compensation curve. That is to say, this kind of compensation and reality have a certain amount of people. In addition, if the actual expansion rate of the 50% tone is 40%, then photoshop will be powerless. At this time we can only make one more compensation in the RIP.
Another method is that in Photoshop, the defined point gain is 0, and the dot expansion of each tone is compensated in RIP. The compensation value is the difference between the measured value and the set value of the sample.
(4) RIP parameter selection. For printing requirements, each color requirement can represent 0-255 levels, printing and dyeing do not have such a high requirement, generally can be controlled between 64 and 128 levels. Screening number: For the printing and dyeing requirements, the screen mesh number is between 98 and 118/cm. For the printing and dyeing process, the mesh number is between 24 and 39 [~/cm can meet the requirements. In order to meet a certain number of tones, an output of up to 60 mesh/inch screens with 600dpi photo output can reach up to 101 levels.
Screen angle: It is recommended that the screen angles of C, M, Y, and K color versions be l5. 75. 90. 45. . If there is a conflict between the silk screen pattern and the color pattern, you may choose to adjust the screen angle and the number of meshes (in general, the number of meshes should not change).
It can be seen from the above analysis that the color separation setting is related to the printing and dyeing process. In order to make the printing and dyeing effect close to the printing effect, when using Photoshop's color separation settings, we can make appropriate choices in its parameters to meet the printing and dyeing process requirements, supplemented with RIP compensation, and then look at the sample effect. Get experience and data.
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