Is there a way to fix this, without having to adjust the photoshop file?
There has to be a conversion for the ink to be limited, so multiplying a dense CMYK color over an image can create total ink problems. There are a couple of possible solutions, maybe someone else will have a better one.
You can set the Transparency Blend Space to RGB, and InDesign's Separation Preview will show the ink limit is being honored because the readout shows the CMYK numbers for flattened document CMYK. The RGB blend space forces all the transparency into RGB and the Sep Preview readout is the conversion back to flattened document CMYK.
If you have black text on the page, it will also read as 4-color black which you probably don't want. Try exporting the page to PDF/X-4 and in AcrobatPro flatten the page with the Flattener Preview tool (keep the blend space as RGB). In that case the black text should remain black:
This is a PDF/X-4 page with live transparency and an RGB blend space showing an area of ink at 345%
The page flattened using Flattener Preview and the same area reads as 300%—SWOP's total ink is being honored.
Acrobat doesn't convert the black text into 4-color—"some text" doesn't show when I hide the black plate:
I'm guessing as long as you export PDF/X-4 you don't really need to manually flatten and the conversion would be correct at output, but flattening gives me the right numbers.
Thanks for the comprehensive reply Rob.
Just changing to the RGB transparency blend space makes the ink limit issue go away, but it changes the CMYK values of logos etc that are defined in Indesign. Am I doing something wrong, or is that an unavoidable consequence of changing the transparency blend space?
I think for us "normal" InDesign users this problem is unavoidable.
We could overcome it by using special device link profiles to control maximum TAC (total amount of color) by a CMYK to CMYK conversion in a PDF workflow.
But this could not be done in InDesign itself and has to be done best on the printer's side.
Eg. with special tools like Colorlogic's ZePrA Server software.
I guess we just have to try to address the problem through Photoshop.
Am I doing something wrong, or is that an unavoidable consequence of changing the transparency blend space?
The RGB blend space is forcing the conversion you need to get the ink limit but ID's blending is to the entire page so all the CMYK objects are going to get re-separated.
I think you have to get the multiplied blend into the RGB Photoshop file, then you'll get the SWOP total ink.
Thanks for clarifying Rob.
Depending on your workflow, a tool like Callas's pdfToolbox with added functionality for using device link profiles could be the answer as well.
Btw. I am not working for Callas, but I think, looking into will not hurt. A new version of pdfToolbox was announced today together with webinars in English and German.