How to trap using Adobe trapping technologies Table of Contents Introduction . 4 What is trapping? . 5 Common printing problems . 6 How trapping solves these problems . 7 Common trapping situations . 8 Methods for avoiding register problems . 9 Trapping details Trapping gradients . 12 The sliding trap . 12 Metallic and spot colors . 13 Varnishes and non printing inks . 13 Images against gradients . 13 Images with complex backgrounds . 14 Images on images . 14 Rich black trapping . 15 Keep-away trapping . 15 Vector-to-Continuous-tone trapping . 16 Text over Continuous-tone images . 17 Trapping clipping paths . 18 Where thin strokes need special handling . 19 Adobe technology solves trapping problems Trap settings . 22 Trap styles . 23 Corner mitering . 23 Adobe trapping technologies and how to use them Adobe trapping in common workflows . 26 Adobe in-RIP trapping . 27 Adobe PDF Trapper . 28 Adobe, the Adobe logo, AdobePS, Adobe Type Manager, Acrobat, Acrobat Exchange, ATM, Distiller, Adobe InDesign® . 30 Extreme, FrameMaker, Illustrator, InDesign, PageMaker, Photoshop, PostScript, and PostScript 3 are Adobe Acrobat InProduction® . 32 either registered trademarks or trademarks of Adobe Systems Inc., in the United States and/or other Adobe PageMaker® . 34 countries. Microsoft, Windows, and Windows NT are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. Apple, Macintosh, and TrueType are trademarks of Apple Computer, Inc., registered in the United States and other countries. UNIX is Adobe technology partners a trademark of the Open Group. All other trademarks are the property of their respective owners. Adobe in-RIP trapping partners . 38 Copyright 2002 Adobe Systems Incorporated. All rights reserved. Printed in the USA. BC2730 4/02 Introduction What is trapping? A problem that has been around since Gutenberg’s time When good presses and good paper go bad In the 16th century, Johann Gutenberg Fortunately, most of Gutenberg’s The sophistication of printing has also Trapping is a prepress procedure that out of register, the edges of touching ordinarily sophisticated—they must had press problems galore! He printed printing was done in a single color– improved, as has the need to prevent introduces areas of color into color colors either overlap, creating an resolve every possible press register from metal type of his own making most of the color ornamentation in press register problems before they separations. When printed, these areas unattractive color intersection, or they error for any combination of colors onto animal skin called vellum. The his famous 42-line bible was added by occur. This is a process of building better obscure potential register errors. spread apart, creating a partial outline and printing elements. problems of press register were not artisans after printing. If Gutenberg presses and processes, and by improving of white paper showing through (See unknown to the famous printer. had decided to print his breathtakingly preventive elements in the artwork These errors are usually caused by the the illustration on the facing page). beautiful bibles in multiple colors, he we prepare for printing. One of these paper shifting or changing shape while If the vellum was too dry, it wouldn’t wouldn’t have been able to keep the preventive techniques is the process of it is printed, or by presses or plates Compensating for register error hold Gutenberg’s secretly formulated colors in register or achieve the quality trapping jobs in advance of printing. that are out of register. As a result, the involves corrective trapping elements ink. So he would gently dampen the of artistry he sought. colors print incorrectly. which can be surprisingly complex, vellum just prior to printing on it. for artwork can have many different Gutenberg avoided trapping Excessive register error is evident colors and types of color intersections. As the paper dried, it changed shape, His solution to press register error when the colors in an image appear causing slight imperfections in was to avoid situations where color blurry, but typical register error is The methods for creating corrective his books. could go out of register. As printing much more subtle. When colors go trapping elements must be extra- has become more precise, so has the need to control paper and press conditions, and the precision of placing one color atop another when printing multiple colors. How trapping solves register problems The background color is set to 100% magenta. The background color is set to 100% magenta. The intended color of the letter is set to 100% cyan. The intended color of the letter is 100% cyan. If the press goes out of register, the cyan letter shifts A trapping element added to the illustration spreads the to the upper-left, creating a partial outline of lighter color (cyan) into the background. In this example, white paper showing through the trapping element is cyan. The thickness of this element … and a partial dark blue outline appears where is typically very small, but it is adequate to cover any the cyan and magenta overprint. anticipated press register error. (The size of the register error and trapping correction are exaggerated in these illustrations to show the effects of misregister and trapping.) 4 5 Common printing problems How trapping solves these problems Production processes contribute to register error When done correctly, trapping does its job behind the scenes Occasionally a press produces printing Paper bounce can cause problems Sometimes the pressure of deadlines Trapping introduces corrective sophisticated and surprisingly subtle. page description while vector-based that is out of register. Reasons can Paper that prints out of register is often cause press operators to run their color elements to a printing job A properly generated element is the trapping provides speed and high- include poorly maintained machinery, caused by the sheet hitting the gripper machines too fast, increasing the In the process of trapping, new right color and shape. quality trap shaping. mishandled printing plates, mis- stop in the press, and bouncing slightly chance of register error. elements are added to the color managed printing data, poor raw backward before the gripper closes. separations. When printed, Today’s creative printing projects call Correcting errors shouldn’t materials, or human error. Press condition is also a cause of press these elements compensate for for trapping elements that are more create new problems In a multicolor press, the sheet is misregister. If machinery isn’t properly potential problems on the press. complex and trapping techniques that When trapping is done well, the new Paper can cause register error handed off from one press unit to the maintained, the press becomes a factor are superior to those used in the past. printing elements don’t show at all; Paper can cause register error if it next, introducing an opportunity for in poor register, creating trapping In general, the amount of error expected With gradients, superimposed images, they fix the problem and remain is manufactured incorrectly. If its paper bounce between each exchange. problems. in a quality printing job is no more than metallic inks, and extraordinary essentially invisible in the process. affinity to water isn’t controlled in If a press is set incorrectly, or if a press half of one halftone dot. Trapping combinations of artistic elements, production,* the paper can change is run too fast for optimum printing elements are usually generated to the trapping must be more capable Over-assertive trapping elements can size slightly on the press, causing conditions, register error occurs more same size, adding color components than ever before. Adobe trapping become visible and create more of a register error. often and more readily. that will cover or fill errors on press– technologies apply precise vector problem than the problem they were if they occur. analysis to all marking operations to meant to solve. combine the benefits of raster- and Trapping systems introduce micro- vector-based trapping. Raster-based scopic elements in ways that are both trapping produces accurate color and 1 2 3 4 EAT The yellow-gold The black object object is lighter than is darker than its AT its surrounding color. surrounding color. A trapping element The trapping element JOE’S spreads into the is choked into the darker color. darker color. The yellow-gold trapping element overprints the background color and prevents register error from appearing as a white gap. Register problems can manifest themselves in a variety of Example 3 shows the effect of white type reversed-out of ways. In example 1, the red is set to knock out the cyan. a rich black. If the press goes out of register, the letters are Simple trapping elements are called “spreads” and “chokes.” If the press goes out of register, the red overprints the compromised; small type can become illegible. Example In the example at left, the yellow-gold object spreads into cyan, creating a dark brown hairline on one edge and a 4 shows the relationship between cyan and yellow in a the black object to prevent register error. In the example on white hairline on the other. In example 2, the yellow text knock-out situation. If the press goes out of register, the right, the yellow background color is choked into the is designed to knock out the magenta. If the press goes out a white gap appears up at the top of the symbol, and a black object. In both cases the yellow-gold trapping element of register, the letters take on a brownish drop shadow. green halo appears at the bottom. would overprint, and it wouldn’t be visible as it is in these illustrations. 6 7 Common trapping situations Methods for avoiding register problems Why trapping is important A number of routes to a trap-free project Colors that touch usually The four common process colors Designing around trapping Avoiding trapping requires care all potential register errors with a This technique has several advantages: require trapping in commercial printing are cyan, Projects designed to be printed Clever designers can avoid the perils relatively thick line of black ink.