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

A ques­tion: what is the dif­fer­ence between these out­put formats when print­ing from InDes­ign? I must admit, its some­thing I wasn’t too clear on. So I decided to hunt down a defin­it­ive answer by doing some intens­ive testing.

Let’s start with an InDes­ign 2.0 doc­u­ment that con­tains many ele­ments and see what changes at print time. There are three pan­els: all of the ele­ments within these pan­els are defined in the col­our space CMYK, RGB or Spot col­our. The Placed PSD is a nor­mal Pho­toshop 7 .PSD file; the four rect­angles are cre­ated in InDes­ign and the placed EPS is saved as an Illus­trator 8 EPS from Illus­trator 10.

Print­ing from InDes­ign 2.0 using Com­pos­ite RGB res­ults in all InDes­ign cre­ated ele­ments and placed bit­maps being con­ver­ted to RGB. Placed EPS or PDF ele­ments stay in their placed col­our mode (RGB or CMYK or god for­bid, both). Spot col­our ele­ments; either cre­ated in InDes­ign 2.0 or placed stay as spot col­our elements.

Print­ing from InDes­ign 2.0 using Com­pos­ite CMYK res­ults is vir­tu­ally the as the above: all InDes­ign cre­ated ele­ments and placed bit­maps being con­ver­ted to CMYK. Placed EPS or PDF ele­ments stay in their placed col­our mode (RGB or CMYK or god for­bid, both). Spot col­our ele­ments; either cre­ated in InDes­ign 2.0 or placed stay as spot col­our elements.

This con­ver­sion is triggered from the doc­u­ment col­ourspaces. You will notice a dif­fer­ent if you turn on col­our man­age­ment, or assign pro­files to bit­maps in the InDes­ign document.

A little Trans­par­ency Flattener Magic

In the above example, this is the res­ult­ing PDF when print­ing Com­pos­ite Gray, but with placed PDF or EPS ele­ments. They are not con­ver­ted to Gray­scale. So, here’s our little tech­nique with trans­par­ency applied.

The Flattener is your col­ourspace con­ver­sion friend. If you take a placed EPS or PDF ele­ment that you are not sure in CMYK or RGB, just set its trans­par­ency to 99.9% Nor­mal. Now when print­ing, this ele­ment is routed through the magic of the Flattener prior to out­put. It sees that your are print­ing “Com­pos­ite CMYK” or “Com­pos­ite RGB” and con­verts the out­put to that col­ourspace. The next ques­tion is “what hap­pens, doesn’t this make it see through? Won’t it blend with the col­ours under­neath?” Well, no. 0.1% is a VERY small per­cent­age, and it rounds back to a full num­ber (evid­ently, some stuff is rep­res­en­ted as integers, so 0.1% of 255 is a 254.75, which rounds back up to 255)

You can also use this to force a doc­u­ment into Gray­scale. Set­ting placed EPS/PDF ele­ments with 99.9% trans­par­ency and print­ing Com­pos­ite Gray res­ults in a 100% Gray­scale PDF [watch for spots!]. Good for News­print applic­a­tions. Be warned; the gray­scale col­ours chosen might not always be what you want at print time.

What about export­ing EPS or PDF?

Yes, this same pro­cess applies.

EPS: you have a choice of CMYK, Gray or RGB. The flattener trick with 99.9% trans­par­ency works here too, as ele­ments have to be flattened in the Post­script stream.

PDF: you have a choice of CMYK, RGB or Leave Unchanged. Again, the flattener is invoked where required.

What is the Dif­fer­ence Between InRIP Sep­ar­a­tions and Com­pos­ite CMYK?

When print­ing InRIP sep­ar­a­tions you are print­ing Com­pos­ite CMYK (as above), but InDes­ign adds some extra Post­script com­mands to the out­put device. This instructs the RIP to gen­er­ate a page per col­our­ant in the file. So, if there is spot col­our in the doc­u­ment, it will be sep­ar­ated onto its own plate.

By the way, Acrobat Dis­til­ler 4 and 5 ignores this “sep­ar­ate” com­mand, and you get a PDF from the Post­script that is the same as a Com­pos­ite CMYK PDF. Except that InDes­ign gets a chance to apply “Applic­a­tion Built-in” trap­ping prior to cre­at­ing the Post­script. (ref: InDes­ign 2.0: Gen­er­at­ing Com­pos­ite, Trapped PDFs)

Dif­fer­ent RIPs have dif­fer­ent set­tings for line screen ruling/angles — and in some cases over­ride what the applic­a­tion out­puts. Usu­ally because “the applic­a­tion gets it wrong” accord­ing to prepress oper­at­ors I speak to.

What is the Dif­fer­ence Between the two Trans­par­ency Blend Spaces?

When Flat­ten­ing two objects at print time, you’ve got to do some math­em­at­ical stuff to determ­ine how col­ours will mix together. The col­ourspace this is executed in may change the effect­ive col­our of the res­ult­ing flattened object. This is sim­ilar to the dif­fer­ence you see in Pho­toshop with some blend modes in RGB vs. CMYK. The recom­mend­a­tion is to set this to CMYK for prin­ted out­put, and RGB when doing on-screen Acrobat 4.0 style PDFs. Acrobat 5.0 PDFs are not flattened at export time. You can also see a subtle change on screen in InDes­ign 2.0.

(my test­ing pro­ced­ure: Print­ing from InDes­ign 2.0.1 through Acrobat Dis­til­ler 5.0.5 using the Press.joboptions [leave col­our unchanged] and check­ing col­ours in the res­ult­ing PDF using Pit­Stop 5.0)