PDF transparency reviewed

This new blog thread is dedicated to the development of the PDF standard and its associated sub-standards. As a delegate of the Swiss Standardization Association (SNV) in the ISO Comittee I'm supposed to review all related working documents. Currently I'm focussing on the working draft of the new ISO Standard ISO 32'000-2 (PDF 2.0), especially the chapter about transparency.

Transparency is one of the most challenging parts in the implementation of a PDF rendering engine since it touches other areas such as patterns, shadings, overprinting and many more. In the first place I checked all formulas describing the blending modes and group compositing rules. This seems to be unnecessary at the first glance but experience shows that some formulas need to be clarified or even corrected. I can still remember, when we were working on the first part of the standard I detected that the coordinate mapping formula for annotations was wrong which remained undetected for more than 10 years! In the new working draft descriptions of the blend modes "ColorBurn" and "ColorDodge" have been improved which now make more sense for me. The good news is that I'm now quite confident that all formulas are now correct since I have derived them independently from the basic description and got the same result as in the published working draft.

If there is some part in then standard that needs clarification in your opinion please let me know. I'm looking forward to discuss this with you. Or, if you need insight into some specific transparency topic just let me know. I would be glad to share it with you.

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