Wrong overprint display

[alexander_duerregger]

Hello!

We have a pdf File from a Customer which has an overprinted text which i assume the overprint view does not show it correctly.

The background color has the CMYK Value 100/50/80/15.

The text has the CMYK Value 0/12/100/0 and is overprinted with opm 1.

From my understanding the resulting CMYK Value for the overprinted Text should be 100/50/100/15 with opm1.

I have attached the PDF, a Screenshot of the resulting display in Acrobat and a Screenshot how i think it should look.

Am i wrong with this?

best regards,

alexander

[JR Boulay]

How did you set the text overprint in InDesign?

[alexander_duerregger]

I only have the PDF as it is a customer File.

[JR Boulay]

It doesn't look like an Acrobat issue.
When I use overprinting in InDesign, I get the same result as in your file (1st screenshot).

To obtain the values you want, you need to use the Darken* mode in Effects (2nd screenshot).

* I'm not sure about the translation because my InDesign is in French, but the items are in the same place.

[alexander_duerregger]

Correct, in Indesign i got the same result. The question is what is the technically correct result. I got different result when i use different RIPs to print the page. For example if i let it process in a GMG Colorserver (which uses the Adobe PDF Print Engine in Version 6.1 i think) i got the same result as if you use "darken" effect in indesign. And i think the result from the processed file in GMG Colorserver is technically correct and the overprint preview in Acrobat is wrong.

[JR Boulay]

"GMG Colorserver is technically correct and the overprint preview in Acrobat is wrong."

I'm not qualified enough to answer this question, but it would mean that the preview is wrong in Acrobat and in InDesign...

[alexander_duerregger]

I know it sounds crazy that the preview could be wrong in both programs. But technically overprint comes from printing one color over another color. and more color in cmyk means means a darker print. The best explanation from OPM 1 that i found is from heidelberg: https://onlinehelp.prinect-lounge.com/Prinect_PDF_Toolbox/Version2021/de/Prinect/Color_management/Co...

And in this explanation my assumption would be right and it should look like the gmg example.

[alexander_duerregger · Accepted solution]

Okay, after reading the pdf reference i think i figured it out. Basically what overprint in OPM 1 does is if the value of the overprinted color is 0 it takes the underlaying color. If the color is not zero it takes the overprinted color.

This is what happens:
Cyan: base color 100%, overprinted with 0% - because of zero it takes the base color with 100%.

Magenta: base color of 50%, overprinted with 12% - it takes the 12% because it is not zero.

Yellow: base color 80%, overprinted with 100% - it takes the 100% because it is not zero.

Black: base color 15%, overprinted with 0% - because of zero it takes the base color with 15%.

I think this implementation is a bit counter intuitive. But that is the way it is implemented. Thank you all for your help!