Do I have to remap 0% "Gray Color" to 100% K black?

Started by Made in Taiwan, March 05, 2015, 12:07:34 AM

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Made in Taiwan

Working in Prepress is very difficult. God chose only the best to do this job.

swampymarsh

#31
Made in Taiwan, I note the following from your two files:

BEFORE: Acrobat Pro Object Inspector reports overprint = False, PitStop reports overprint = False

AFTER: Acrobat Pro Object Inspector reports overprint = True & OPM1, PitStop reports overprint = True & OPM1

EDIT: As Matt said, overprint on gray does not work, gray must be converted to separation black or to 0cmy?k for overprinting to work correctly.

Even the Acrobat Pro colour conversion tool has the option to "promote gray to CMYK" and to preserve black.

For an overprinting object: OPM0 shows a knockout, while OPM1 shows an overprint – which makes turning off the black separation in the output preview inconsistent and confusing as the overprint flag is true in both cases.

swampymarsh

After some more tests:

If the overprinting black content is set to "separation: black (process colour)" – then it does not matter if the objects are set to OPM0 or OPM1, they consistently overprint.

If the overprinting black content is set to "CMYK" – then the only way for the overprint to be recognised appears to be to use OPM1.

So my conclusion is to always use OPM1, whether or not one is using separation black or CMYK objects, and to play it really safe, black only objects can also be set to separation black as extra insurance.

elko

Why overprint for device gray objects dont work propertly?? It is a separation as any spot. I understand that spot has alternate CMYK representation but essentially device gray is K separation....

abc

It's Gray, in a Grayscale workflow (that it is designed for) what can it overprint?
I guess you would need to read the PDF specification to find out the technical reasons

elko

I understand that single-channel-color-space doesnt need overprint but I mean an object. I could have a pdf...there are used any color spaces you can imagine (CMYK, RGB, spot, GS, LAB and so on).....output should be offset CMYK+1spot....... one GS object and one spot object  have overprint.... I am looking for differencies..... two one-channel spaces GS and spot color, for one is overprint reasonable and for the second it is not.....

abc

You can't overprint CMYK either. so if you have a spot color with overprint and convert it to CMYK, overprint doesn't work
There's a trick to set it to overprint 'multiply' with an Action List or you can covnert to Device N.

This kind of stuff is tricky indeed, thank god for overprint preview.

Farabomb

Yes thank god for it.

God now needs to tell designers about the function.
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