When people face print, they always feel that dark colors are close to human eyes and light colors are far away from the human eye. Therefore, when trapping a manuscript, he always tries to prevent dark colors from appearing. The dark color above remains unchanged to ensure that it does not affect the visual effects.
Trap handling principles
The implementation of trapping should also follow certain principles. Under normal circumstances, it is to expand the color and not to enlarge the color, to enlarge the light color and not to enlarge the dark color, and to expand the flat screen without expanding the ground. Sometimes it is also possible to carry out mutual expansion. Under special circumstances, trapping is reversed, and even a gap between two adjacent colors is required to make up for the overlay error, so that the prints are beautiful.
The size of the trapping volume depends on the characteristics of the printing materials and the overlay accuracy of the printing system. Generally, the trapping volume of offset printing is smaller, and the trapping volume of gravure printing and flexo printing is larger, generally 0.2-0.3 mm, which can be determined according to the printing accuracy or requirements of customers.
Common trapping methods
There are four common trapping methods.
(1) Monochrome line superimposition method: add light-colored lines on the edge of the color block, and select line attributes as overprint.
(2) Synthetic line method: add synthetic lines on the edges of color blocks. Line attributes are not selected as overprints.
(3) Layering method: Trapping is realized by indenting or externally expanding elements on different layers.
(4) Shift method: By moving the position of the inflection point in the color block to achieve shrinkage or external expansion, it is generally used in trapping related to gradient.
The following discussion is based on the example of a trap size of 0.2mm.
1. When the color blocks are adjacent to the color blocks, a monochromatic line superimposition method or a synthetic line method is mainly used.
(1) When the cyan block is adjacent to the magenta block (including various combinations of percentages of different dots), the monochromatic line superimposition method is adopted, that is, the magenta block line is changed to 0.4 mm magenta, and the attribute is selected as superimposition. line. If the synthetic line method is adopted, that is, the line of the magenta block is changed to a C100M100 line of 0.2mm, and the attribute should not be selected as an overprint line. Here, the monochromatic line superposition method expands the magenta block toward the cyan block by 0.2 mm, and the combined line rule is that the magenta block and the cyan block each expand 0.1 mm toward each other, which is a form of mutual expansion.
Magenta is adjacent to yellow. Cyan is similar to yellow when adjacent, or a 0.4mm yellow line is added and superimposed; or a 0.2mm M100Y100 (or C100Y100) line is added.
(2) When the superposition color of any two colors of cyan, magenta, and yellow is adjacent to another color, including the combination of different dot percentages, the trapping process adopts the monochromatic line superimposition method, which expands the monochrome block by 0.2 mm in the superimposed color. .
(3) Red consisting of magenta and yellow in percentage of different outlets, and blue in percentage from different outlets. When yellow is adjacent to the green, it must be trapped. Otherwise, overprinting will lead to leakage of yellow. Red lines can be added with red lines. Lines are superimposed on the overprinted lines to trap.
2. If the color block is formed by superposition of two primary colors or spot colors of the same size and position, there is a transparent or white surrounding, so as to prevent the overprint from leaking out of the next color and cause unsightlyness, the next color contraction method can be used to trap. India. If the color patch is formed by two flat mesh colors, or if the previous color is a flat screen and the next color is a field, trapping is generally not required unless there are special requirements for printing.
3. When the gradation is adjacent to the color patch, it is divided into the following situations.
(1) Cyan gradient and magenta. When yellow is adjacent, trapping is performed according to the printing color sequence, and magenta or yellow can be extended by 0.2 mm in the cyan gradient.
(2) When the magenta gradient is adjacent to the cyan block, reverse trapping is required, that is, cyan is extended to 0.2 mm in the magenta gradient. When the magenta gradient is adjacent to the yellow block, normal trapping is performed, and the yellow block is expanded by 0.2 mm toward the magenta gradient.
(3) When the yellow gradient is adjacent to the cyan and magenta blocks, reverse trapping is performed. The cyan and magenta blocks are extended by 0.2 mm in the yellow gradient.
4. There are two types of trapping when contiguous tone images are adjacent to color patches: one is to expand the color patches into the image; the other is to expand the edges of the image into the color patches. When expanding the image edge, you can slightly enlarge the image according to the actual situation, or use image editing software to enlarge the edge of the image, or enlarge the mask of the image. When the four-color image is adjacent to one or more of the primary colors, trapping is generally not required. If the color hue of the patch differs greatly from the hue of the image, trapping is required. For example, when the red tomato pattern is adjacent to a green block, the green block must be extended to the tomato pattern.
When a four-color image is adjacent to a spot color, it must be trapped.
Spot colors and primary colors. Spot colors and spot colors. The trapping between spot colors and gradients, spot colors, and images can be based on the principle of trapping and the trapping method described above, and will not be repeated here.
Black, gold and other special traps
Black, gold, silver and other special traps generally follow the following rules.
1. When the black and gold blocks are adjacent to other colors, other colors are darkened and the gold blocks are enlarged, and can be expanded to 0.5-1 mm.
2. Generally black and gold text is superimposed directly on the background.
3. Patterns with black and gold contour lines, pattern fill color and adjacent background color are best stacked in the middle of black and gold lines to avoid trapping unevenness.
4. Under normal circumstances, relatively small black and gold blocks can be directly superimposed on the background color; larger black and gold blocks need to be overprinted with the background color in order to save ink, and the background color can be extended into black and gold blocks.
5. Although the hiding power of black and gold ink is strong, it also has a certain degree of transparency. When large black and gold blocks are stacked on two different colors, black, gold and background colors are used to ensure a consistent visual color effect. Should use overprinting.
6. When the black and gold blocks are directly overprinted on the background, and there are white characters or thin lines on them, if the area of â€‹â€‹the black and gold blocks is large, the black and gold blocks and the background color should be overprinted if the area is relatively small. Small, white text or thin lines can also be reduced to avoid the white, white lines after printing.
7. When black is adjacent to gold or silver, trapping can be performed according to the printed color sequence. Under normal circumstances, black can be overprinted in gold or silver. If the area is large, it is best to make overprints to avoid printing difficulties.
In plastic packaging printing, white ink applications are quite extensive. Generally, in the printing of transparent or translucent plastic, it is necessary to make the bottom in white, and sometimes also to hold two layers of white. In order to prevent the white underneath the excellent block from being exposed due to overprinting, a white retraction should be considered before printing.
1. The white retraction can be performed according to the depth of the color or the customer's request. The retraction amount is generally 0.2-0.3mm.
2. If the color block is white and the side is transparent, white can be retracted to 0.3 mm.
3. Black and gold under the care of the white, the white can be retracted to black, gold 0.5-1mm.
4. If the color of the color block is light or flat, the amount of white retraction should be small or not retracted. For example, when the percentage of the dot of the color patch is between 30% and 50%, the amount of white retraction may be 0.15 mm; and when the percentage of the dot of the color patch is less than 30%, the white may not be retracted.
5. When whitening under the gradient pattern, white should be considered for oblique retraction. Under the cyan gradient, the color is white, and the cyan is dark where the white color shrinks by 0.2 mm, and the cyan color is where the white color shrinks by 0.1 mm. The inflection point shift method can be used now.
6. If the transparent color (under the ink is not white) is adjacent to other colors, the white color under other colors should be 0.2mm; if the transparent color is directly adjacent to the white, the white color should be extended to 0.2mm to the transparent color to avoid leaks. .
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