Persons in the industry know that plain printing uses UCR (bottom color removal) or GCR (non-color structure) yellow, magenta, cyan, and black (ie, Y, M, C, K) four-color plate making in the reproduction of color images. law. This is determined by the actual printing conditions, including the characteristics of the printing substrate, ink, and printing method (the latter two most important). The black version plays an indispensable role in modern printing. However, in the gravure printing process, is it also necessary to print in the same way as the non-printing method of Y, M, C, and K? This is the topic that this article will discuss.
First, the basic theory of color knowledge
1. The properties of the color. Any color can be described with hue, saturation (also known as color), and brightness (in color psychology, also known as brightness), ie HSB, where H=Hub is the hue, S=Seturation is the saturation, and B=Brightness For brightness.
A hue is the most essential feature of a color. For monochromatic light, hue refers to the wavelength of the color light, and for multicolor light, it refers to the proportion of each monochromatic light it contains. From the visible light of 380 nm to 780 nm, the hue of the visible light changes in turn from the purple column red.
2 Saturation refers to the purity of the color light contained in the color light. Reflected by the amount of white light contained in the color light, the more white light contained, the less light contained therein, and the lower the saturation thereof. The more saturated the color is, the more vivid the appearance effect is.
3 Brightness refers to the intensity of the color light. When the intensity is large, the brightness is large, and the color of a person's clothes feels bright. Otherwise, the color becomes dark.
2. Color space. In the real world, natural light is colorized by additive coloration; colorants, such as pigments or dyes, are color-reduced. Therefore, such as sunlight in the natural world and the color rendering of the display, the three-color method of RGB (ie, red, green, and blue) can be used to describe its color appearance. In printing, YMC (ie, yellow, magenta, and cyan) can be used. Three color method to describe. This involves the problem of a color space. Each color space has a range of colors that it can represent. Among many color spaces, the color space of sunlight is the largest, the color space of the display is secondarily, and the color space of printing is the smallest. That is to say, the color that the printing can reproduce is the least.
3. The same color spectrum. For the human eye, the final cell can stimulate the sensation of RGB color, that is, the color of the human eye to identify the principle of color. Therefore, for the human eye, the color light and the color material are equivalent, which results in a metamerism phenomenon. The so-called metamerism means that the two colors have the same appearance, but the spectral characteristics of the two may be completely different. Use a formula to describe the image:
Color=(x1)R+(x2)G+(x3)B=(z1)Y+(z2)M+(z3)C
Note: where R=Red, G=Green, B=Blue, Y=Yellow, M=Magneta, C=Cyan
This principle is the basic principle of printing three primary colors YMC to reproduce various colors in nature.
4. The achromatic component in the color. Gray and black are achromatic, only the size of the brightness changes, and no hue, saturation, they belong to achromatic components. However, non-color components include not only gray and black, but also include non-color components in color.
In printing chromatics, yellow, magenta, and cyan are called primary colors; the colors that are mixed from any two of the primary colors are called secondary colors, and they are called interspersed colors such as red, green, and blue; and all The color of the three primary colors is called the third color, also called the complex color. The colors that Y, M, and C are mixed in different ratios (any one color is not 0) must contain a complex color. This complex color is the most interesting part of the printing plate making, and this is the most basic principle that UCR and GCR structures can be used in printing plate making. We can decompose any color into two parts of neutral gray and color. Neutral gray can be copied by black ink, and the color part is still copied by the original color. Thus, the color of the two added and the color mixed directly with the three primary colors The effect is the same.
Second, the color removal (UCR) and non-color (GCR) structure
1. What is UCR and GCR. Both UCR and GCR use the principle of containing non-color components in the polychromatic color, which can be replaced by black ink, except that the amount of black ink used to replace the polychromatic image in the range of the original gradation is different. UCR is limited to the dark tone in the original, except that the black or dark gray part of the image replaces the achromatic component in the complex color with black ink, while the GCR is in the full tone range of the original, from high light to dark tone. The entire image area is full-color-removed, ie, the black version is a full-tone version. Any color in the image is reproduced by black ink and any one or two or more colors.
2. Why use UCR and GCR. Early offset printing was done with photographic color separation. UCR and GCR structures were not used. All non-color components in color were reproduced by primary colors. With the economic development, printing has gradually moved toward electronic color separation and desktop publishing systems, as well as four- or more-color high-speed printing. At this time, there have been three technical difficulties. First, how to solve the problems of multi-color printing ink drying, dirt on the back of the back, ink supply and gray balance; second, how to save expensive color ink, reduce costs; Improve printing quality and stability, provide printing suitable wet wet plate. This type of printing plate requires that a small amount of ink be transferred to the paper without losing the brightness and thickness of the color, and the GCR structure solves these problems just fine.
Of course, adopting the GCR structure completely is not compatible with the actual situation. In practice, due to the limitations of various conditions such as paper, ink, and printability, if the GCR is used completely, it will result in a dark tone and a lack of solidity. Therefore, based on the GCR, the actual plate making production uses the UCA (Background Gain) structure. The UCA is a neutral gray that does not completely replace the color with black ink. It is only partly replaced, and a small part of it is neutral. The ash is still mixed by the three primary colors, so as to avoid causing the dark portion of the image to be thin (ie, insufficient in density) and not thick.
Third, the actual production of the actual situation
1. The color gamut of different color spaces will be different. The inks used in actual production are characterized by insufficient reflection and excessive absorption, that is, lack of basic color, opposite colors, and large differences. Compared with sunlight in the natural world, there is still a certain gap, so each primary color ink will have Color cast, not ideal complex light. For example, the color shift of yellow ink is 11%, the color shift of blue ink is 26%, and the color shift of magenta ink is 35%. The ash content of each color is above 15%. These reasons determine that the color gamut that can be reproduced by printing must be smaller than the color gamut of daylight and smaller than the color gamut of the display. This difference can be clearly seen in the CIE horseshoe gamut. The colors that are difficult to reproduce in printing are mainly high-saturation, low-brightness colors. This part of the original color is often replaced by the closest color in the printing system. This results in distortion when reproducing the original, but this distortion is unavoidable and can only be improved from the material to the process, minimizing the distortion.
2. Printing method. There are several types of plates, such as lithographic, letterpress, gravure, and stencil printing (also called missed printing). (Other non-pressure printing, such as copying, electrostatic printing, etc. are not discussed here.) Each printing method has its advantages and disadvantages, and the color space that can be reproduced also has a size difference, which is determined by its printing substrate, printing ink, and the amount of ink that printing can transfer.
3. There are many types of manuscripts that can be printed. They can be roughly divided into photographs (colored and non-colored), drawings (such as various hand-painted drawings), prints, and color negatives (mainly color reversal films). The color reversal film has the best quality and the price is much more expensive than other originals. In lithographic platemaking, all originals except for the reversal film can be substantially completely copied without gradation compression, while for the color reversal film some of its shadows must be compressed. For high-quality printing, the original document used is a color reversal film. Particularly in gravure printing, most original four-color printing uses a color reversal film. The color reversal film reproduces the color by the dye. A total of three dye layers, respectively, R, G, B light sensitive. It can also be seen here that there is no dye layer that is sensitive to the neutral gray component alone in the color reversal film. This color positive film has the following characteristics:
1 After exposure and photography of objects, after reverse rinsing, a color positive film of the same color and the same light and shade level as the object is directly generated. Because of its one-time imaging, the number of copying is reduced, thereby reducing various levels. Loss of density. Therefore, the distortion is very small, and the color of the object is quite similar.
The colors that can be reproduced by the 2 are very vivid, the picture is very clear, the levels are quite rich, and the picture contrast is extremely large. It is suitable for six-fold magnification. The density range it can reproduce is as high as 3.0, which is much higher than the color photo 1.8.
First, the basic theory of color knowledge
1. The properties of the color. Any color can be described with hue, saturation (also known as color), and brightness (in color psychology, also known as brightness), ie HSB, where H=Hub is the hue, S=Seturation is the saturation, and B=Brightness For brightness.
A hue is the most essential feature of a color. For monochromatic light, hue refers to the wavelength of the color light, and for multicolor light, it refers to the proportion of each monochromatic light it contains. From the visible light of 380 nm to 780 nm, the hue of the visible light changes in turn from the purple column red.
2 Saturation refers to the purity of the color light contained in the color light. Reflected by the amount of white light contained in the color light, the more white light contained, the less light contained therein, and the lower the saturation thereof. The more saturated the color is, the more vivid the appearance effect is.
3 Brightness refers to the intensity of the color light. When the intensity is large, the brightness is large, and the color of a person's clothes feels bright. Otherwise, the color becomes dark.
2. Color space. In the real world, natural light is colorized by additive coloration; colorants, such as pigments or dyes, are color-reduced. Therefore, such as sunlight in the natural world and the color rendering of the display, the three-color method of RGB (ie, red, green, and blue) can be used to describe its color appearance. In printing, YMC (ie, yellow, magenta, and cyan) can be used. Three color method to describe. This involves the problem of a color space. Each color space has a range of colors that it can represent. Among many color spaces, the color space of sunlight is the largest, the color space of the display is secondarily, and the color space of printing is the smallest. That is to say, the color that the printing can reproduce is the least.
3. The same color spectrum. For the human eye, the final cell can stimulate the sensation of RGB color, that is, the color of the human eye to identify the principle of color. Therefore, for the human eye, the color light and the color material are equivalent, which results in a metamerism phenomenon. The so-called metamerism means that the two colors have the same appearance, but the spectral characteristics of the two may be completely different. Use a formula to describe the image:
Color=(x1)R+(x2)G+(x3)B=(z1)Y+(z2)M+(z3)C
Note: where R=Red, G=Green, B=Blue, Y=Yellow, M=Magneta, C=Cyan
This principle is the basic principle of printing three primary colors YMC to reproduce various colors in nature.
4. The achromatic component in the color. Gray and black are achromatic, only the size of the brightness changes, and no hue, saturation, they belong to achromatic components. However, non-color components include not only gray and black, but also include non-color components in color.
In printing chromatics, yellow, magenta, and cyan are called primary colors; the colors that are mixed from any two of the primary colors are called secondary colors, and they are called interspersed colors such as red, green, and blue; and all The color of the three primary colors is called the third color, also called the complex color. The colors that Y, M, and C are mixed in different ratios (any one color is not 0) must contain a complex color. This complex color is the most interesting part of the printing plate making, and this is the most basic principle that UCR and GCR structures can be used in printing plate making. We can decompose any color into two parts of neutral gray and color. Neutral gray can be copied by black ink, and the color part is still copied by the original color. Thus, the color of the two added and the color mixed directly with the three primary colors The effect is the same.
Second, the color removal (UCR) and non-color (GCR) structure
1. What is UCR and GCR. Both UCR and GCR use the principle of containing non-color components in the polychromatic color, which can be replaced by black ink, except that the amount of black ink used to replace the polychromatic image in the range of the original gradation is different. UCR is limited to the dark tone in the original, except that the black or dark gray part of the image replaces the achromatic component in the complex color with black ink, while the GCR is in the full tone range of the original, from high light to dark tone. The entire image area is full-color-removed, ie, the black version is a full-tone version. Any color in the image is reproduced by black ink and any one or two or more colors.
2. Why use UCR and GCR. Early offset printing was done with photographic color separation. UCR and GCR structures were not used. All non-color components in color were reproduced by primary colors. With the economic development, printing has gradually moved toward electronic color separation and desktop publishing systems, as well as four- or more-color high-speed printing. At this time, there have been three technical difficulties. First, how to solve the problems of multi-color printing ink drying, dirt on the back of the back, ink supply and gray balance; second, how to save expensive color ink, reduce costs; Improve printing quality and stability, provide printing suitable wet wet plate. This type of printing plate requires that a small amount of ink be transferred to the paper without losing the brightness and thickness of the color, and the GCR structure solves these problems just fine.
Of course, adopting the GCR structure completely is not compatible with the actual situation. In practice, due to the limitations of various conditions such as paper, ink, and printability, if the GCR is used completely, it will result in a dark tone and a lack of solidity. Therefore, based on the GCR, the actual plate making production uses the UCA (Background Gain) structure. The UCA is a neutral gray that does not completely replace the color with black ink. It is only partly replaced, and a small part of it is neutral. The ash is still mixed by the three primary colors, so as to avoid causing the dark portion of the image to be thin (ie, insufficient in density) and not thick.
Third, the actual production of the actual situation
1. The color gamut of different color spaces will be different. The inks used in actual production are characterized by insufficient reflection and excessive absorption, that is, lack of basic color, opposite colors, and large differences. Compared with sunlight in the natural world, there is still a certain gap, so each primary color ink will have Color cast, not ideal complex light. For example, the color shift of yellow ink is 11%, the color shift of blue ink is 26%, and the color shift of magenta ink is 35%. The ash content of each color is above 15%. These reasons determine that the color gamut that can be reproduced by printing must be smaller than the color gamut of daylight and smaller than the color gamut of the display. This difference can be clearly seen in the CIE horseshoe gamut. The colors that are difficult to reproduce in printing are mainly high-saturation, low-brightness colors. This part of the original color is often replaced by the closest color in the printing system. This results in distortion when reproducing the original, but this distortion is unavoidable and can only be improved from the material to the process, minimizing the distortion.
2. Printing method. There are several types of plates, such as lithographic, letterpress, gravure, and stencil printing (also called missed printing). (Other non-pressure printing, such as copying, electrostatic printing, etc. are not discussed here.) Each printing method has its advantages and disadvantages, and the color space that can be reproduced also has a size difference, which is determined by its printing substrate, printing ink, and the amount of ink that printing can transfer.
3. There are many types of manuscripts that can be printed. They can be roughly divided into photographs (colored and non-colored), drawings (such as various hand-painted drawings), prints, and color negatives (mainly color reversal films). The color reversal film has the best quality and the price is much more expensive than other originals. In lithographic platemaking, all originals except for the reversal film can be substantially completely copied without gradation compression, while for the color reversal film some of its shadows must be compressed. For high-quality printing, the original document used is a color reversal film. Particularly in gravure printing, most original four-color printing uses a color reversal film. The color reversal film reproduces the color by the dye. A total of three dye layers, respectively, R, G, B light sensitive. It can also be seen here that there is no dye layer that is sensitive to the neutral gray component alone in the color reversal film. This color positive film has the following characteristics:
1 After exposure and photography of objects, after reverse rinsing, a color positive film of the same color and the same light and shade level as the object is directly generated. Because of its one-time imaging, the number of copying is reduced, thereby reducing various levels. Loss of density. Therefore, the distortion is very small, and the color of the object is quite similar.
The colors that can be reproduced by the 2 are very vivid, the picture is very clear, the levels are quite rich, and the picture contrast is extremely large. It is suitable for six-fold magnification. The density range it can reproduce is as high as 3.0, which is much higher than the color photo 1.8.
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