Re: Bug with overprinting in Mark II/IV?

[Peter Rolf <indiego@gmx.net>]

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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
>
>   


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