Electronic trapping: computer-controlled register control by Brian P. Lawler for newsprint, and the amount of that trap are different than those needed for higher quality printing processes (see chart on page 3). The Graphic Arts Technical Foundation uses three terms to describe the difficulty of printing a job: hairline register (often called tight register), loose register, and lap register. Hairline register requires colors to abut Changing terms with no unprinted Trapping has evolved paper showinginto a term to describe through, and no the process of intentional intentionally overlapping of colors overlapping colors to (no trapping). When a compensate for register job is designed with error on the press. loose register, colored Though the term objects are spaced is used widely in the enough apart that electronic prepress register problems will industry, there may be not easily be visible. some confusion as we In other words, move forward with the because the objects integration of have enough open electronic prepress in space between them conventional printing that a little more or plants. less space will not be Conventional noticeable. Lap register printers, new to the jobs have built-in terminology of the The images on the left are in perfect register, but the images on the register compensation right have slipped out of register on the press, creating white spaces electronic prepress – trapping – making industry, may need to on parts of the image, and overprints of the combined color on the them easier to keep in others. Trapping is the process of creating intentional overlaps of become aware of the register on press. changing terminology. color that prevent the white from showing when a press goes out of This is the most register. There are many methods for trapping, and many technical Communications and considerations to take into account. common kind of education are needed register used in in both printing and prepress. commercial printing, but the cost of preparing the Whether you choose to use terms like spreads overlapping traps is significant, and estimators and chokes, shrinks and spreads, grips, lap register, or must plan on having their prepress staff build traps fatties and skinnies is unimportant. Regardless of into jobs, unless those traps are created what you call the technique, be sure to trap, for electronically at an earlier stage of production. without correct trapping, we cannot get excellent You might assume that everything would be printing – and excellent printing is our objective. easier if we just paid a higher price for printing in hairline register and forgot about trapping. It’s not Register that easy. A broad range of mechanical, In the context of trapping, register is the accurate environmental and human factors combine to positioning of two or more colors of ink on a make it very difficult or impossible to keep printed sheet. The requirements for correct register printing in absolute register. This is the simple vary from one printing process to the next. The reason for the existence of color trapping tolerance for register error on newsprint is usually techniques in prepress and design. different that the tolerance on coated sheet-fed printing papers. Therefore the need to trap colors
What is trapping?
Trapping is the intentional overlap of colors in a printed project that prevents the almost-inevitable register errors in printing from showing. It is compensation – in advance of production – for the human and mechanical errors that can result in misregister of images on a printing press.
© 1995-1998 Brian P. Lawler. All rights reserved.
ELECTRONIC EDITION
v.7•10/2/98
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