The trapping function and its application in commonly used DTP software
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Trapping is the last step in the prepress process. Its function is to compensate for the blank gap caused by non-absolute registration in printing or the chromatic aberration caused by the image separation step. Trap is generally invisible during prepress production, and traditional output proofing in the DTP process is a means of verifying the process.
The halftone reproduction of image reproduction (visual mixing of four-color dots in the human eye) and the non-absolute registration of the substrate in printing are the theoretical and practical reasons for the trapping process. In the prepress process, the CMYK color separation information (film point) is the knock out, overprint, spread and choke work in the four-color step. Trap.
The trapping as described above is the first function of trapping. Continuously adjusting the image will also have a tone step when the screen is separated. Normally, RIP will trap it when it is connected to the network. Although Photoshop provides the Trapping feature, it is generally not recommended. Unless you are very sure that your head is as sophisticated as a computer.
Experienced graphic producers know that pulling gradients in Photoshop is better than lining in AI or FH. Of course, the AI or FH output should be set to a file accuracy higher than 2400 DPI. I think the reason is that RIP supports different trappings when bitmaps and vector description languages are connected. (Example: a gradient: c80% m30% y20% to m10% y60% bk20% need to be a trap, or else the overprinting during printing is likely to cause gradient color leakage.)
Trap is a process after page grouping, so it is a wise choice when exporting film or zinc. (So the DTP software that can be issued has the trapping option when it is issued. For example, in the FH ordering option, there is a color version full-overprint (usually black version) option, as well as in a color version. The option to completely overprint from a certain percentage tone.) However, the current active RIP has only limited trapping capabilities. Dedicated trap software requires a dedicated workstation, such as TRAPWISE from Cresace Angel. The complexity caused by a series of factors, such as the post-printing process, makes it often time and money in many cases, but it does not necessarily have a good effect. In the future full digital process, ADOBE's POSTSCRIPT LEVEL 3 trapping system is expected to solve this problem at the RIP level.
Nonetheless, thanks to our computer software writers' base and object programming ideas, we can use the corresponding features of DTP software to do some simple, inexpensive trapping. For example, in the commonly used page layout software, a reasonable trapping preset parameter is set, and the vector graphic element is manually trapped in the vector software. Before doing the trapping, let us first talk about the relevant basis of trapping.
Trap foundation
In the pre-press separation process, the relationship between the four-color film is generally done by the back-end RIP.
There are basically two kinds of separations: overprint or knockout. (If c100%m50% of the color block is reflected on the four-color film, it can also be regarded as c100% overprint m50%).
The rest of the yk version is hollowed out. In the four-color printing process, the other three color inks can be overprinted in the black solid area of the printing plate. (In special cases, other three-color inks are overprinted from 95% black, depending on the situation).
So in all software we can set the bk100% page element to overprint. But if there are black page elements straddle on other graphic information. We generally cannot choose overprint.
We can only perform knockout processing on this element separately (or set the black to bk100%y1%) or set the black to rich black, which is to add other component colors in black, such as black 100%. C60%. To avoid the difference in visual density due to ink overprinting.
When dealing with large black areas, we tend to add c30% to the black. Because black ink is an inorganic ink, it lacks luster. In this case, trapping is also required (setting the trapping parameters in the imposition software).
If the document has some opaque color plates: such as gold, you can overprint it.
But if there is black on the gold, then we can't overprint the black election, it can only knockout. At the same time, make a spread on the edge. Make a few lines (0.1-0.2pt) on the edge of the black or gold version, which should generally be greater than the printing overprint accuracy. Then make an overprint for this wireframe separately.
Generally speaking, it is safe to do the trapping between black and spot colors with strong coverage, because sometimes you don't know the color of the print.
This principle is used in the manual trapping of all prepress software. Among them, QuarkXpress has the strongest and most professional trapping function.
Let's take a brief introduction to each software one by one. The explanation about the numerical setting and related terms is not specific enough. Because the actual production situation of each company is different, it can only be used flexibly under the principle of mastery.
Successful trapping requires the basic knowledge of color separation plate making, careful design, and the interrelationship between each page element (object) in the layout. The following is an introduction to commonly used software. (Please refer to the corresponding settings for PC users)
u page layout software trap settings:
Quarkxpress, Pagemaker, and Indesign 2.0 all have built-in trapping capabilities. Among them, Quark's trapping function is the most comprehensive. They only make up the following information:
1. Elements generated in the page software. Such as text, lines, patches, and borders.
2. An object generated by the page software that overlaps with the imported bitmap image.
That is to say for the objects imported in the imposition software, EPS or bitmap. It should have done the correct trapping itself.
For the former, we will talk about how to make traps in vector production software. For the latter, I think everyone has a concept. Using Trapping in Photoshop sharpens the subtle levels of the image.
The trapping in Quark can be controlled in three ways:
1. Auto trap: The Quark output is trapped according to the set value in the “Trip Preset Parameters” dialog box.
To access the trapping preset parameters, select the document under the Edit menu and click the Trapping option. Be careful not to open any Quark documentation at this time.
2. Color-to-color trapping: This trapping is created directly in the color definition, and these values automatically override the auto-trapping value.
Select the color dialog under Edit, select the color you want to edit, and then click the Trapping button to display the Trapping Information dialog.
3. Object-to-object trapping: This trapping uses Quark's Trap Information floating panel to trap individual objects of the file.
Individual objects can be trapped by selecting the Trapping Information panel under the Window menu.
In summary, trapping is a process of deconstructing the color information of the full layout and then making corresponding color correction at the color step. And trapping is based on the concept of trapping, using the relevant software features to trap some simple page elements. A more comprehensive trapping implementation is based on program level or RIP level.
From this perspective, we can only expect better development of trapping software and the development of other related processes and materials to be able to get rid of the pre-press trap.
(Trapping).
Drawing software, group software, special trapping software
Purpose Create a simple trap manually or automatically Create a trap in the group software. Generally, the raster file is rasterized and then trapped.
Isolated element none none none
Overlap with a single element Create a simple manual trapping Automatic trapping preset in software Automatic trapping
Overlap with multiple elements. Built-in Trap tool. Automatic trapping presets and Trap tools in the software. Automatic trapping.
Overlap with imported elements Use overprint strokes at the edges of the elements Turn on foreign objects using trapping in software (not commonly used, more difficult to control) Allows users to have more control
The imported EPS object can't be trapped. Generally, it can't be missed.
Imported bitmaps can't be trapped. Generally, it can't be leaked or limited. Automatic trapping but time is unpredictable.