I went through PDF 1.7 reference and Pitstop Pro to understand the difference between OPM 0 and OPM 1.
I have clearly understanding on none-zero overprint mode now.
However,I got questions on OPM 0.
1)If the default OPM from Illustrator is OPM 1,and there is also "knockout" definition when the overprint checkbox is not selected ,how could I generate OPM 0 definition from Illustrator or other creative application? So far I could just change the definition in PitStop Pro.
2)What's the result difference between the definition of OPM 0 and knockout?
Looks like they are the same, when viewing the different objects as OPM 0 and knockout in Acrobat Pro and also in creative application,with overprint viewing is selected.
- OPM always only can impact DeviceCMYK vector, text or imagemask objects
- it controls whethere these objects migth overprint Cyan, Magenta, Yellow or Black
- overprint will only happen, if one or more colorant values for the DeviceCMYK object are 0.0
- it will only kick in if op or/and OP are already set to true
this implies the following:
- if op/OP are false, it does not mater what value OPM has
- if op/OP are true but OPM is zero, a DeviceCMYK text, vector or imagemask object will always knock out Cyan, Magenta, Yellow and Black, even if some or all of the colorant values for the DecviceCMYK object are 0.0
Thank you for your answer,forgive me that it doesn't address my question.
1) How to create OPM 0 object from Illustrator or from other application?
So far in Illustrator I just get OPM 1 object when overprint is on and knockout when overprin is off.I need to see object defined as OPM 0 from creative application.
2) What's the result difference between OPM 0 and knockout?If it's the same on the final drawing ,what's the point to have OPM 0 and knockout as different definitions?
OPM only has an effect if op/OP is alerady true. Once op/OP are false it does nto matter what value OPM has. SO for an application like Illustrator thereis no need to set OPM to zero if op/OP are false.
Why would you need OPM equal zero?
Illustrator only works in the OPM 1 world. It has done since long before PDF was invented. It is rare for an application to give control over OPM, generally it works in only one overprint model.
There are three cases to think about with overprint.
1. Overprint off. This is often called knockout. OPM is ignored.
2. Overprint on, OPM 0.
3. Overprint on, OPM 1.
Be sure you understand this and what effect they will have.
Does both of you imply that OPM 0 doesn't have real application and meaning here ?
However, in some prepress workflow( like in Prinergy),there is checkbox to change OPM 0 to OPM 1 during PDF normalize.From then I suppose there would be some occasions to get OPM 0 object.
Another doubt I have is ,I couldn't see any difference between OPM 0 and knockout.
For example,I put OPM 1 and knockout vector on some background,change the OPM 1 object to OPM 0(by PitStop Pro plugin in Acrobat Pro),both OPM 0 and knockout has the same knockout result.
So if OPM 0 has the same behavior,why does it still call overprint instead of knockout?
Not at all. OPM has meaning. It just has no meaning when overprint is off.
"Overprint off" is the same thing as "knockout".
OPM neither turns overprinting on, nor turns it off. That is a separate setting. You still do not seem to be working with the THREE cases I described. Look closely to see which one(s) are the ones you are testing. If you read my cases carefully you will see that So if OPM 0 has the same behavior,why does it still call overprint instead of knockout? is not right.
After I went through the following table (from PDF reference document) I get better understanding of OP state and OPM .
Previously I just ran test on CMYK and didn't get the difference result from knockout and OPM 0.When it applies to Spot and other color space,there is difference.
Thank you for your replies.
PS, do anyone know how to create OPM 0 object from any creative application?