[poppler] Implementing overprint in Splash

[Albert Astals Cid]

A Dijous, 24 de març de 2011, Thomas Freitag va escriure:
> On 24.03.2011 21:14, Albert Astals Cid wrote:
> > A Dijous, 24 de març de 2011, Thomas Freitag va escriure:
> >> I don't know if this patch is useful without the outstanding overprint
> >> patch for Splash, but I finished implementation of the two new options:
> >> 
> >> -overprint renders the PDF in in splashCMYK8 first and converts the CMYK
> >> Splash bitmap to RGB during writing (compiler switch SPLASH_CMYK must be
> >> set on pdftoppm and on poppler library). It's implemented for png, jpeg
> >> and tiff, tested for png and jpeg but should work with tiff, too.
> >> USE_CMS is not implemented in the moment, the conversion from CMYK to
> >> RGB is done with a copy from the GfxState-routines.
> > 
> > Why copy the functions?
> 
> There are "static inline" in the Gfx header files. I could include the
> header file in Splash, but that means that we begin to mix splash and
> poppler :-(

There is copy in Splash using the error() function already, so it's nothing 
new :D

> 
> >> -jpegcmyk produces a jpg in CMYK colorspace (compiler switch SPLASH_CMYK
> >> must be set on pdftoppm and on poppler library).
> >> 
> >> Because overprint is not implemented yet, the overprint option changes
> >> nothing in the moment. So this option can be used as a zero state for
> >> overprinting to see which PDF renders differently with the outstanding
> >> first implementation of overprinting.
> > 
> > Don't understand this.
> 
> -overprint option(!) simply renders in splashModeCMYK8 and during
> writing it is converted to RGB, so the better option would probably be
> to render it directly in splashModeRGB8. But overprint functionality(!)
> is naturally only defined in a CMYK colorSpace, therefore we need
> splashModeCMYK8 for the overprint functionality. But because overprint
> (functionality) is not really implemented in splash with this patch, the
> output should nearly the same (nearly, because without the option we
> directly render in RGB, with the option we render in CMYK and convert
> CMYK to RGB afterwards).
> What I mean with zero state: I just run the create MD5 script with this
> patch to have an initial MD5 value, assuming, that the output is correct
> (because nothing is really changed in the underlying functions).
> Tomorrow I'll run my roughly tested overprint patch against this and
> examine, what pdf have changed. If these changes fit to specifications,
> I'll upload the overprint patch to the community.

So we add an option that does nothing (to the end user, that's it)? I'd prefer 
that not to happen.

Albert

> 
> Hope, this clearifies it,
> Thomas
> 
> > Albert
> > 
> >> Thomas
> >> 
> >> Am 21.03.2011 20:47, schrieb Albert Astals Cid:
> >>> A Dilluns, 21 de març de 2011, Thomas Freitag va escriure:
> >>>> Hi all!
> >>>> 4. Support of overprint in pdftoppm
> >>>> To support overprint in pdftoppm we have to enable SPLASH_CMYK in
> >>>> pdftoppm and use it for rendering. But all output formats defined in
> >>>> pdftoppm uses RGB as output colorspace, and even the main output
> >>>> formats ppm and png do not support CMYK colorspace. Therefore we have
> >>>> to possibilities to support overprinting in pdftoppm:
> >>>> a) The easiest way would be to specify a new output format like i.e.
> >>>> jpegcmyk and create a jpeg image in CMYK colorspace where overprinting
> >>>> will be supported.
> >>>> b) The more interesting way is to add a new parameter -overprint, when
> >>>> set use splashCMYK8 as colorMode and when writing the output file
> >>>> convert it to RGB. The first implementation could use the poor
> >>>> colorspace conversion in Splash to convert the CMYK bitmap to RGB, but
> >>>> we should think of use little cms to do that work for us, which of
> >>>> course means that compiling pdftoppm will become more complex.
> >>>> 
> >>>> Any suggestions from the community to point 4?
> >>> 
> >>> Both seem interesting :-)
> >>> 
> >>> Albert
> >>> 
> >>>> Thomas
> >>>> 
> >>>> _______________________________________________
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