[pdftex] Overprint/Knockout with \pdfobj / \pdfximage

[JEBs]

Hi (again),

I'm totally desperate in trying to activate PDF's overprint possibilities.

Background:
I'm building a DB export which builds via pdflatex a 4C pdf document, 
which shall be printed in a professional printing agency (of course in 
cmyk).
The whole document has a light-yellow backgound !
Till now I calculated the underlaying CMY fraction on top of the text's 
black color definition which works in general, expect that it inhibits 
last time changes which may occur when already in the printing agency 
(i.e. by PitStop ...).

I already posted this short question some week ago to this mailinglist, 
but didn't found a solution till now.

In addition to my text-color problems, which may work in general via the 
underlaying color calculation, I've now the same problem with images too :(.

The document uses eps/ai vector diagrams which are converted via "gs" to 
PDF images.
The vector image content itself is well formatted with op/OP/OPM/TK 
attributes and the converted PDF image contains them too,
but when I place them into my document (on top of the yellow background) 
all black elements are printed "knocked out" on the underlaying color 
(which is in gerneral as defined because the PDF default values specifiy 
exact this behavior) !
With that knocked out lines and texts, the whole document isn't 
professional printable !
In germany we call that behavior "streaker" (blitzer).

Both of my problems (text & images) are easily configurable with PDF's 
op/OP (overprint), OPM (Overprint mode) and TK (Text knockout) 
attributes, EXCEPT I'm to foolish how to use them with \pdfobj, 
\pdfximage, \pdfliteral or whatever.
I already tried a lot combinations but didn't got ONE working.

I know that it has something to do with the "Graphics State" 
structure/parameter block and tried to use/activate it as \pdfobj or 
\pdfpageattr but again, NONE of my tries returned the correct results.

Is there anybody out there who can help me in the syntax/usage or has a 
sample for me ?


TIA
    JEBs