I am Stupid - I don't know how to prep indesign PDF's for offest printing CMYK - help

Sean Dempsey

macrumors 68000
Original poster
Aug 7, 2006

I've been printing digitally so long, I don't know how to do indesign files for offset plates!

I have exported my PDF, but now in the seperation preview, my black isn't very black, and the places where I have transparency or the black on top of other colored objects, the objects beneath show through!

I know that offset printing doesn't like transparencies, but I thought that exporting the PDF would flatten it so that the CMY plates didn't get any information where the black overlays it (like big black text on top of a photographic image).

But instead, it does output the CMY colors beneath the black areas, so when it prints the black plate on top of it finally, you can see the colors underneath. Does this make sense? It doesn't flatten the final PDF and knock out the areas where black occludes the rest of the CMY areas.

If I go through in Indesign and change my black(K) things to Registration, it solves the problem, but then that means that the CMY plates then ALL print 100% and then the black plate prints 100% as well... and I don't think that is right.

So, what do I do? I tried exporting it as the oldest, flattest PDF preset that indesign does, and it still has the problem. I've Googled "flattening PDF's from indesign" but can't seem to get the answer I want.

Does all of this make sense to anyone who has had to output stuff for offset CMYK printing?


macrumors newbie
Feb 19, 2006
I have concerns about you trying to use Registration as a color, so here is this from the same site.


Printers usually have a stock Rich Black that they use. Ask them what the mix is.

I agree. Using registration as black can cause the ink density to become too high thus resulting in muddy, blotchy tones. For example, my printer uses a formula of 40C 30M 30Y 100K as their rich black.


macrumors member
Jun 29, 2004
Saint Paul, MN
Meh, googled my own question:


here's the answer in case MRoogle ever cares.

(hint - don't use 100K, add some CMY to it so it knocks out the overprint)
There is also a setting in InDesign's preferences (Appearance of Black) where you can toggle off the automatic overprint at 100% black. For CMYK work rich black is best for areas where type covers an image or graphic element, but when it's alone with nothing behind it ("black on white") you should use 100% black so you don't have to worry about registration issues, especially in thinner font styles.

If you get into spot color work, you will need to be more careful about what does and doesn't overprint if you have areas of different colors coming in contact with each other. Never be afraid to ask your local printer, we'd rather answer questions and help designers learn about printing than have to call you when things aren't right and try to fix things that could cost you more in prepress.

Sean Dempsey

macrumors 68000
Original poster
Aug 7, 2006
I found most of this out from reading that site.

I got rid of all the registration colors and used a Rich Black mix, fixed everything.

The printer I am working with says they use a Digital CMYK, so it's seperations, but digitally printed?

Designer Dale

macrumors 68040
Mar 25, 2009
Folding space
Every color must have it's own separation, no matter how the press works. I think digital presses work like advanced copiers with toner drums of CYM and K instead of ink towers. This means that the content of each color plate can be loaded onto drums in the form of an electrical charge rather than a physical plate. The result is the same. four colors applied to a sheet of stock one at a time. So they still need your separations in PDF format.

I'm out of the industry now, and most of my knowledge is in offset.


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