How do you know about trapping methods of common desktop publishing software?

Image processing software Photoshop, graphic processing software Illustrator, Freehand, and desktop publishing software such as Pagemaker, QuarkXpress, and Indesign all support trapping processing, but there are differences in trapping processing.

1. Trap processing of image processing software

The image processing software uses the dot matrix method to describe the "content information" to be expressed, and its trapping processing function is also implemented by a dot matrix method. There are two different ways of trapping using the dot matrix method. First, color blocks are used for the foreground and background colors. The computer analyzes all boundary pixels of the image and then selects the average value of all the pixels to complete trapping. The advantage of the trapping method is that the trapping processing speed is faster, but the printing overlay error is obvious; second, the foreground and the background color are continuously adjusted images. At this time, the trapping processing is usually set at both ends of the image boundary in advance. The trap width selects the middle color as the trapping color for each pair of adjacent pixels on the boundary, so that almost no border is seen on the printed matter.

The steps to set trapping in Photoshop are as follows: Open a color image and convert it to CYMK color mode; type magenta Chinese character “printer” on a cyan background, and then merge the layers; select the menu Image/Trap, The dialog box shown in Figure 3 appears. Width in the dialog box is the width of the compensation boundary. The value is directly related to the offset of the color plate at the time of printing. The numerical value is equal to the sum of four-color printing overprint errors. Width (width) has three units: Pixels, ranging from 1 to 10; Points, ranges from 0.01 to 9.99; mm, and ranges from 0.01 to 3.53 mm. Set the trap width value to 3 Pixels and click OK to get the result shown in Figure 4. It can be seen from the figure that the M color and C color permeate each other to form a blue edge.

In fact, in addition to trapping between patches in Photoshop, trapping can be performed on continuous tone images. The result of this processing is generally to expand the brightness of the lower pure colors into a certain trap. width. However, people are not recommended for use in normal production.

2. Graphics Processing Software and Pattern Processing

Trapping in software

Graphics processing software and template processing software are based on the vector method to deal with trapping. The trapping vector processing method is a layout composed of vector graphics and text elements. The page description of this layout adopts a mathematically strict geometric description method, that is, using a straight line, a circle, and a cubic Bezier curve and its color filling to complete the pairing. Description of all profiled objects. The trapping process is based on the boundary between two different colors. The lighter side expands toward the darker side to form a new boundary line. This trapping method can better handle fine patterns and text trapping. Print, but bitmap color images cannot be processed.

(1) Setting Trapping in Illustrator

Select two or more objects and choose Window > Show Path Manager.

In the Path Manager palette, click the Trapping button in the lower-right corner of the dialog (if the Trapping icon is not displayed, select Show Options from the pop-up menu).

In the dialog box, you can set trapping thickness, height/width, and hue reduction. What is the specific setting of the thickness range in print production depends mainly on the printing paper and printing equipment. The "height/width" ratio refers to the ratio of horizontal trapping to vertical trapping. The inconsistent horizontal and vertical trapping values ​​can compensate for inconsistencies during printing, such as paper stretching. The "Hue reduction" value is used to change the color tone of the trap. The default value is usually 40%. The "Hue reduction" value will reduce the value of trapped brighter colors; the value of darker colors will remain at 100%.

In addition, there are two options related to trapping in the dialog box. Whether to use "Print trapping with printing" and whether to use "Reverse Trap", select "Trap with Printing" to create a brighter color Trapped to a darker color, the object "reverse trapping" is used to trap darker colors into lighter colors.

(2) Trap processing in PageMaker

PageMaker's trapping information is controlled by the Trapping Preference dialog in the File menu.

The trapping value that the trapping parameter dialog box can define is also a range. You can set the trap width, trapping threshold, and black attribute.

There are two settings in the Trap Width setting box: 1 Default Trap Width setting; 2 Width when black is trapped, which is normally set to 2 times the default Trap Width. There are three settings in the trapping threshold setting box: 1 The “Step Limit” value determines the PageMaker trapping point. Increasing or decreasing this value determines how much of the various ink components are trapped before PageMaker traps. The lower the percentage, the more PageMaker traps between colors. The "centerline trapping threshold" is in the range of 0% to 100%, which means that we can set anywhere from 0% to 100% of the threshold range. At 0, all traps are set on the centerline. At 100%, the trapping of the centerline is avoided, resulting in complete external expansion or retraction. 3Trap Text Above determines the minimum font size that PageMaker uses for trapping.

In the Black Properties dialog, one can set black limits and auto-overprint black settings. The black limit setting determines black or ultra-black. Automatic Overprinting Black Let us decide that the black line and fill color will trap or overprint. At the bottom of the dialog, there is an option to trap the images entered by PageMaker.

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