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Nick Hodge is a Professional Geek for Microsoft Australia. More info lives underneath the About Box...

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InDesign 2.0: Generating Composite, Trapped PDFs

By Nick Hodge | February 8, 2003

Visit the new InDes­ign Prepress Sec­tion: Adobe InDes­ign: Prepress Tech­niques

Gen­er­at­ing Com­pos­ite, Trapped PDF from InDesign

Well cre­ated, Com­pos­ite PDFs are the most com­monly reques­ted format for print­ers in this part of the world. So, how exactly do you gen­er­ate a com­pos­ite, trapped PDF?

InDes­ign 1.5.x and 2.0.x have sup­port for Applic­a­tion Built-in trap­ping. The trap­ping engine inside InDes­ign matches many of the fea­tures of Adobe’s InRIP trap­ping engine; usu­ally found in higher end RIPs from Creo, Heidel­berg, Agfa etc.

Trap­ping is the pro­cess of chan­ging the shapes of cer­tain objects in a prin­ted out­put to reflect the way the ink will run when prin­ted. Each of the inks are laid down on the paper by dif­fer­ent cyl­in­ders of the press. As the paper (sub­strate) are impressed by these cyl­in­ders, there might be a mis­reg­is­tra­tion — where the inks don’t quite line up. In this instance, the plates con­tain extra over­prin­ted areas of dots to cover up any unsightly gaps that may be left in the final output.

Highend PDF work­flows today are bedev­illed by the “Who is trap­ping this?” ques­tion. In con­trolled work­flows, this is easy to coordin­ate. Prepress know which press a job is run­ning on, and apply some visual checks on the job and may make trap­ping changes to the source file prior to out­put. How­ever, when there is a hand-off to an unknown press and print­ing envir­on­ment, the cre­ator will not know the press con­di­tions. Today’s digital work­flows largely assume that the final RIP (imagesetter/platesetter) will trap the document.

In some work­flows, this trust may not be enough. We need to make com­pos­ite PDFs for onscreen view­ing, sim­pli­city and size; yet trap them so there are no ugly white patches at print time.

With InDes­ign 1.5 and 2.0, the Adobe trap­ping engine takes InDes­ign cre­ated object (text and vec­tor objects) and traps them to placed images, text and vec­tor shapes. InDes­ign does not trap placed PDF or EPS objects. These are assumed to be trapped. InRIP trap­ping solu­tions will trap the entire page stream. To use Adobe In-RIP Trap­ping, you must use In-RIP sep­ar­a­tions. Built-in trap­ping lim­its trap widths to 4 points, regard­less of the value you enter for the trap widths. For lar­ger trap widths, you will need to use Adobe In-RIP Trapping.

From QuarkX­press, the trap­ping inform­a­tion as setup by the Trap palette only comes into play when print­ing sep­ar­a­tions. With QuarkX­press 4.0 and above, over­print­ing and knock­outs as set by the palette are retained in com­pos­ite Post­script out­put. Sav­ing Pages as EPS from QuarkX­press 3.32 and higher does res­ult in overprints/knockouts being retained. (see QuarkX­press, PDF, Trap­ping and Over­print)

InDes­ign 1.5.x and 2.0 pre­serve knockout/overprint attrib­utes in Com­pos­ite Post­script out­put. As you would expect, Adobe’s Applicaton Built-In trap­ping works when print­ing separations.

Back to the topic at hand: A sig­ni­fic­ant work­flow dif­fer­ence with InDes­ign is that it can also apply Applic­a­tion Built-In traps when print­ing InRIP separations.

What are InRIP sep­ar­a­tions? Essen­tially, pro­grams like InDes­ign send com­pos­ite Post­script to the RIP with some extra com­mands telling the RIP to take a com­pleted page and pro­duce n-plates based on the col­our­ants on the page. For simple pro­cess jobs, this would res­ult in a page each for C, M, Y and K.

The imple­ment­a­tion of the Post­script showpage and copypage oper­at­ors have the cap­ab­il­ity of pro­du­cing pages for each col­our­ant. If the out­put device doesn’t have this col­our­ant, then the altern­at­iveSpace col­our­ant is used; fail­ing this, DeviceCMYK is used. There is a Post­script engine inside the Dis­til­ler, and it yields DeviceCMYK col­our­ant output.

Acrobat Dis­til­ler has a Post­script engine inside: what does it do with InRIP separation-marked Post­script? Dis­til­ler 4.0x and 5.0.x ignore the oper­at­ors for pro­du­cing pages for each col­our­ant, and pro­duce a com­pos­ite PDF. The col­ours stay as CMYK (or spot col­ours if used) if the Dis­til­ler options are left to “Leave Col­our Unchanged”

Now InDes­ign 1.5.x and 2.0.x allow you to apply Applic­a­tion Built-in trap­ping to the com­pos­ite Post­script when print­ing as InRIP sep­ar­a­tions. Yes, I know its a little mind bend­ing! If you then send the res­ult­ing Post­script to Acrobat Dis­til­ler, the Dis­til­ler dis­cards the com­mands to sep­ar­ate, but it does retain the extra “trap­ping” Post­script com­mands. The final PDF holds these trap com­mands, and they can be viewed in Acrobat 5.0 by turn­ing on Over­print Preview.

The final out­come is a Com­pos­ite, Trapped PDF.

Steps

1. Ensure that your Trap­ping set­tings are cor­rect. Please con­sult the InDes­ign CS Print­ing Guide, the manual and your Prepress/Printer before assum­ing the defaults are correct.

2. Assign a Trap Style to the page. In this instance, I am using InDesign’s [Default] Trap style as viewed above.

3. Here is the File>Print dia­log box. In Out­put, Color is set to In-RIP Sep­ar­a­tions, and Trap­ping is set to Applic­a­tion Built-In

4. To make it easier to use the same set­tings on the next doc­u­ment, you can save a Printer Style for later use.

5. This is the source doc­u­ment in InDes­ign 2.0

6. The final PDF inside of Acrobat 5.0, (avail­able here: Example Com­pos­iteT­rapped PDF)with Over­print Pre­view turned on. The darker areas around the type etc. dis­play where over­prin­ted strokes have been applied based on the ink­ing requirements.

7. Using Quite Reveal­ing from Quite Soft­ware, I can also reveal the over­prin­ted strokes separately.

For more inform­a­tion about Trap­ping, and spe­cific­ally the Adobe trap­ping engine:

Adobe Trap­ping Tech­no­logy (white paper)

Adobe In-RIP Trap­ping Workflow

How to Trap Using Adobe Trap­ping Technologies

Thanks to Steve Amerige, Matt Phil­lips for their assist­ance with some of the finer details.

Topics: mungenet | 9 Comments »