InDesign 2.0: Printing Output Choices and Flattener Tricks (including force Greyscale export!)

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)