I have "Preserve pure black" selected and I fill the object with CMYK 0,0,0,100. This looks pure black on Corel Draw display, so far so good. But, when I export PDF, it appears as dark grey on the screen. How to achieve blacks appear as 0,0,0 for RGB and 0,0,0,100 for CMYK in an exported PDF?
Nevermind, I figured... In order to achieve the black I describe above, I had to;
* Fill it with [Greyscale L:0] instead of CMYK or RGB black* Publish PDF with Native output colors WITHOUT embedding the profiles!
So, Acrobat displays the greyscale black as RGB 0,0,0 on the screen and prints CMYK 0,0,0,100 to the printer. Phew!
coreltom said: Nevermind, I figured... In order to achieve the black I describe above, I had to; * Fill it with [Greyscale L:0] instead of CMYK or RGB black* Publish PDF with Native output colors WITHOUT embedding the profiles! So, Acrobat displays the greyscale black as RGB 0,0,0 on the screen and prints CMYK 0,0,0,100 to the printer. Phew!
The CMYK-to-RGB color managed conversions do not guarantee that CMYK 0 0 0 100 is converted to RGB 0 0 0. This is why "Preserve pure black" box is often necessary to be checked. If you use Native output mode in PDF Draw will not convert CMYK colors to RGB using "Preserve pure black", it will leave CMYK colors unchanged, as it should. The Acrobat then will convert CMYK colors to RGB in order to be able to display them on the monitor ( which is always RGB ), at that point you would get this "problem" back. If you have "Preserve pure black" checked in Draw and select RGB output mode in Export to PDF dialog it will be us who converts all CMYK colors to RGB on export and CMYK 0 0 0 100 will be converted to RGB 0 0 0. Converting all document colors to RGB might not what you need workflow-wise though.
The behaviour is mostly specific to CMYK colors though, and it is not even a problem, both Draw and Acrobat are doing exactly what they are supposed to do. You do not need to use Grayscale color model whenever you need to define a black color, pretty much anything except CMYK would work fine for your purposes - RGB, LAB, HSB, HLS, Grayscale. It has nothing to do with embedded color profiles.
If your PDFs are for Web distribution and viewing then using CMYK colors in the document and "Native" output mode at the same is unlikely a good choice, converting everything to RGB is usually safer there. If you use PDFs to send jobs to print shops or as print output proofs for the clients it is best to use "Native" mode, embed color profile and let Acrobat to display colors accurately, even though it will render RGB and CMYK blacks differently.
Gennady