Oliver Heins schrieb:

Hi Peter,

Peter Rolf <indiego@gmx.net> writes:

Oliver Heins schrieb:

Hello,

with color black overprinting is not working.  You can easily spot this
when you use the »Ausgabevorschau« (sorry, my acrobat is in german
locale, must be something with »preview« in english; located in the
»tools« menu) in acrobat and remove magenta and black from the preview.
Whilst under the region with the magenta colored text the picture gets
shown, in the region with the black colored text the text is cut out of
the picture, leaving white.

I think the visible 'knockedout' text on the picture is just another
acrobat bug. I manually checked the text and the OVP attributes are
correctly set. If you use the coloring mechanism (Ausgabenvorschau -> 
Farbwarnungen -> [x] Überdruck anzeigen), you will see that everything
looks ok.


Yes, I noticed that, too.  But to me it looks like it is first knocked
out in the pdf, and then the overprint flag is set.

Good point. In that case the text must be set twice, as knockout and overprint can't coexist. I have looked into the uncompressed mkii PDF (\nopdfcompression) and I can not see any obvious flaw. The parts are clearly separeted by '/GSknockout gs' and '/GSoverprint gs', the black text is not set twice.

Just an idea: the colorspace of the picture is RGB, the text is set in CMYK. Maybe the mixed color spaces mess up things here.

I made a document with scribus, which looks alright in acrobats preview:
http://www.sopos.org/olli/overprinting-scribus.pdf

Same here. The difference is, that the picture here is also set in CMYK. So this points to the 'colorspace mess' theory too ;)

So I doubt that this is a bug in acrobat, but in context or even in
pdftex/luatex.

you have to manually copy the hacker.jpg to your working directory
(under linux e.g. with cp $(kpsewhich hacker.jpg)
/path/to/your/working/directory) and change the path to make the
minimal example work under mark iv.

I noticed this too (no picture with mkiv). BOF = Bug Or Feature :)


Feature, as Taco kindly pointed out :-)

Regards,
 olli