When desktop started to emerge as a possible alternative to traditional prepress methods, printers everywhere began to cringe at the possibility of losing control over the quality of the negatives produced. Unfortunately, the printers were often times right! Many of the responsibilities for quality negatives and plates have shifted from craftsmen trained in apprenticeships for 4 to 6 years to designers and publishers inexperienced in the technical issues of prepress and offset presses. Therein lies the reason for this article. If you intend to do your own trapping, the following guidelines may help you in your effort. If the complexity of your project makes the job too confusing you are better off letting your printer handle the trapping and trying these methods on a simpler job. In any case check with your printer. He may have an automatic rip-based trapping solution or a program that he would rather use to get the job done with little or no human intervention and a lot faster than doing it yourself.
It is not my intention to discuss all possible methods of desktop trapping but only the few necessary to the success of the basic job. These methods will save you a lot of grief, time and money if used consistently in cooperation with your printer.
First let's define trapping. In the simplest of terms, trapping is the overlapping of printable items which are touching, in order to prevent any paper show-through in the event of a slight misregistration on the printing press.
As you can see in the above exaggerated illustration, objects that are exactly the same size, when printed a tiny bit out of register, tend to show white (paper color) lines around the objects. On the contrary objects "spread" or "skinnied" to each other so that they overlap tend to have better success when printing on an offset press. In order to sread or skinny an object we have to use tools and objects included in the programs we use to add to or takeaway from these objects as well as get them to overprint in areas that are touching.
Object Oriented Trapping: The term, Object Oriented Trapping, simply means singling out each object that is touching an object of a different color and supplying a "trap" or overlap for that object. While QuarkXpressTM, provides autotrapping, programs such as Adobe Illustrator and Macromedia Freehand have autotrapping features which are not as straight forward. If you use these features it may be a wise idea to use 100% values for trapping. The main thing is not to be afraid of trying new things with either of these programs which you are already familiar with.
Rules of the Road: A few simple rules will assist you in trapping effectively and accurately, but keep in mind that these rules may vary in certain situations.
Generally, however:
1. If it makes a difference, always distort the lighter color. This rule holds true especially with items that will become noticeably distorted, such as type and thin objects.
2. In IllustratorTM or FreehandTM, use a stroke twice as much as the trap you need, as a stroke runs down the center of the original object leaving one-half on the outside of the object and one-half on the inside. (Quality offset printers require a trap of .003" or about .25pt so a stroke needs to be .5pt to fulfill this requirement. Check with your printer to be sure.)
3. Remember that most earlier versions of these programs, the color black makes a straight knock out of anything it overlies. If you do nothing to black objects and type, you will have disastrous results down the line. If you want it to overprint, you will have to change the object's attributes to overprint before you create the EPS file. Later versions changed the default to black overprints everything.
4. Remember to think about where your illustration is going to be placed. If it is going to be exported and placed on top of a color or another object in a page layout program you will have to supply traps in your illustration.
Specifically: IllustratorTM & FreehandTM
Almost anything can be stroked and an overprint value applied in these programs. You simply add a stroke to your object of the same color. Make the stroke .5pt (or ask your printer what he prefers) and check the Overprint box. If you already have a stroke around an object of a different color, for example a red circle with a 10 pt green stroke, things get a bit more complicated. If you were to mark the stroke to overprint the result would be a 5 point area of a combination of red and green (brownish black).
In a case where a large stroke is already present around an object, you need to place a copy of the object directly on top of the older object. Next mark the fill of the new object to be "None"(allowing the original object's fill to show through). Now add .5pt to the stroke size of the object. Finally check the stroke box to Overprint. The same procedure applies to a stroke with no fill or to a line. A problem exists with trapping a line in this fashion in that a line's end points will not trap. A work-around to this problem is to move the end point of the top overprinting rule a hair outside of the bottom rule, or change the endcaps to round or square with the end points recessed. You may also use the option to change strokes into compound objects and supply a new overprinting stroke to the new object(Filter>Objects>Outline Path Illustrator 5+).
Trapping in QuarkXpressTM: QuarkXpressTM has a nice set of trapping controls as well as automatic trapping. There are however some things to be aware of.
1. When Quark autotraps it does not always do it in the most intelligent way. If you have a text box just barely touching a picture box or any other colored object, any colored text in the text block will be spread the auto amount. Have you ever seen fat type in a document that you thought your printer may have changed for no good reason. This little quirk in Quark is usually the culprit!
2. Postscript has limitations, especially with regard to process colors and gradients. This usually results in a straight knockout when you want a spread. You can sometimes override these defaults using the trap information palette found under the View menu.
3. Whenever you use the special bitmap borders that come with Quark, be prepared for trapping problems. If you want a double border and you need the elements to trap, you may have to supply your own trap by creating two windows with frames.
4. Quark measures trapping amount in real terms, not like IllustratorTM or FreehandTM where you have to enter twice the amount you need. We have found a good value to be .25pt to enter into your Trap Preferences dialog box. Enter .25pt in both Autoamount and Indeterminate boxes. Make sure the auto method is marked Absolute.(If you go to Edit>Preferences>Trapping while no documents are open and set your traps, they will be the default in all your documents.)
Trapping in Adobe PagemakerTM: Previous to version 5.0 there really were no tools for trapping. Version 5.0 is barely adequate for objects, and there are no trapping features at all for type. Trapping is achieved by setting a stroke around an object and marking it to overprint in the Objects Fill and Stroke dialog box much like FreehandTM or IllustratorTM. Any type that needs to be trapped should be trapped and imported from Illustrator or Freehand. PageMaker 6.0 + has trapping built in for PageMaker objects. There is no provision for non-Pagemaker elements though. If you mix EPS files Tiffs and PageMakerTM Objects you cannot trap them. We have also found the trapping to be unreliable in many instances with unpredictable results. PageMaker is on the right track though and I think future revisions may give Quark a run for the money, which should make things better for all concerned.
A few hints and suggestions: Try to keep production technicalities in mind when considering a graphic design approach. No matter how brilliant your creative concept, it is of little benefit if it cannot be realized effectively in print. More often than not, the simple, clean design will print with a minimum of technical problems and deliver on time.
1. Dark-colored thin type and objects should overprint a light background whenever possible, even if it changes the color of the object a little. Nothing looks worse than a trap line that's as large as the object it was spawned from.
2. Try to avoid trapping medium unlike colors such as red and gray. This will result in a dark line around the object.
3. Try to avoid knocking out or trapping thin, tiny, italic or serif type faces. They will almost always cause some type of technical problem.
4. If you are not sure whether an object traps, check the object's attributes!
5. Process builds do not have to be trapped if there are enough common colors in each overlapping object.
6. Please above all, if there is a question don't hesitate to ask! Its better to ask a seemingly stupid question than to wind up with an obvious mistake on press.
7. In our prepress preflight of your job we look for trapping problems, and in most cases set traps for our customers. If there is an enormous amount of extra work with traps we will alert you and give you the option of trapping the file yourself or allowing us to do it. We appreciate that your job is design and sometimes your time is best spent doing what you do best and allowing us to do what we do best.
Please E-mail me with any questions or comments.
