Trapping process overview

Effect Design Common Software Package photoshop

Trapping is also known as trapping, also known as scaling, mainly to compensate for the trapping of two adjacent colors due to inaccurate printing.

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 without expanding the dark color, and to expand the flat screen without expanding the actual 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 main trapping methods.

(1) Monochrome line superimposition method: add light-colored lines on the edge of the color block, and select the line attribute 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 different dot percentages), 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 0.2 mm, 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. The situation is similar to when cyan is adjacent to yellow, or a 0.4mm yellow line is added and overprint is selected; or a 0.2mm line of M100Y100 (or C100Y100) 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 monochromatic block by 0.2 mm in the superimposed color. .

(3) Red consisting of the percentages of different outlets of magenta and yellow, and the percentage of blue 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, and the 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 printing two flat meshes, 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, and the cyan and magenta blocks are extended by 0.2 mm in the yellow gradient.

4. There are two kinds 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, the other colors are black 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 outline 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 a large area of ​​black and gold blocks is 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 ​​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 white and 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.

White trapping

In plastic packaging printing, white ink applications are quite extensive. Generally, in the printing of transparent or translucent plastics, it is necessary to use white as the bottom bracket, and sometimes 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, 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 (no white ink under ink) 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 color, the white color should be expanded by 0.2mm to avoid the gap between transparent colors. .

Trapping of common software

In common packaging design software, trapping can be performed manually or automatically.

1. Trapping of the base vector

Lllustrator and FreeHand are vector-based graphics processing software. They can generate simple automatic trapping objects, and the functions of automatic trapping are basically the same. They all create a single light-colored overprinting pad to cover adjacent color blocks. They can determine when traps need to be trapped between adjacent color patches, when they do not need to be trapped, and trap only selected objects.

Open the Trapping tool panel in the PathFinder command under the "Window" menu of the lllustrator software; call the Trapping panel in the "External Function\Create\Trap" of the FreeHand software. The options described here are as follows.

Width (lllustrator/FreeHand): The width of the trapping area. The default value in lllustrator is 0.25 points, and the range is 0.01-5000 points; In FreeHand, you can enter the unit, such as 0.2mm.

Color reduction (lllustrator/FreeHand): This is to reduce the proportion of bright colors in the trapping area so as to reduce the discoloration in the trapping area. The default value is 40%.

Reversed trapping (lllustrator/FreeHand): Changes the trapping direction so that dark colors expand into bright areas.

Automatic trapping in the lllustrator and FreeHand software can only handle traps between adjacent fill patches, and trapping of fill patches and patterns of strokes, gradients, continuous tone images, and other features cannot be trapped.

The lllustrator and FreeHand software automatically traps according to the brightness of the color. The trapping rules are as follows.

(1) All colors expand into black.

(2) Bright color expands into dark colors (including spot colors and other colors).

(3) The arrangement of the primary colors' brightness is from dark to light: M, C, and 丫. That is, when the magenta filling is adjacent to the cyan filling, the color is expanded from cyan to magenta, and this is in accordance with the order of K, C, M, and 丫 printing colors. The trapping method of the time is just the opposite. This is the place to pay attention to.

2. Trapping processing of base sub-bitmap

Trapping in Photoshop is done under the trapping command in the software's "Image" menu. It only has an option for trap width.

Photoshop software traps only by expanding the color. The rules for trapping are as follows.

(1) All colors expand toward black.

(2) Bright color expands to dark colors.

(3) The yellow color expands toward magenta and cyan.

(4) Extension of cyan and magenta peering, ie, mutual expansion.

Also need to pay attention to the following matters.

(1) Consecutive tone images do not require trapping themselves.

(2) The pattern can only be used with the trapping tool when pressing the platform layer.

(3) When the color patch and the color patch are trapped, there will be a fracture at the corner.

Professional trapping software

Professional trapping software is a powerful tool to solve trapping problems. At present, many RIPs provide inrip traps, which are open trapping functions in RIP. However, this trapping method sometimes cannot achieve a satisfactory trapping effect, nor can it be corrected manually; if the design draft needs trapping more or more complicated, trapping with RIP is often an unpleasant experience. The waiting process.

There are also some professional packaging design software such as PACKEDGE, ARTPRO and other powerful trapping modules, but these trapping functions can only be used in their own software systems. Users must also purchase software and trap modules at the same time. Can use trapping features. At present, these softwares have not reached the level of popularity with respect to the sub-general design and pre-press publishing workers.

Now, Esko-Graphics has launched a new DeskPack software, which mainly solves the problems existing in trapping.

First of all, DeskPack provides plug-ins embedded in tlllustrator, which can perform various trapping operations and controls directly in the lllustrator software. Its trapping function module (TrapX) is very powerful.

1. It utilizes the latest brightness based