[pdftex] bitmap with clipping path

Stephan Lehmke lehmke at ls1sol02.cs.uni-dortmund.de
Thu Apr 11 17:16:51 CEST 2002

Stephan Lehmke wrote on Thu, 4 Apr 2002 11:18:40 +0200 (MET DST):
> I have the following problem:

Following up to myself...

It seems I was looking in the wrong direction after all,
and the solution is as easy as I originally hoped it
would be.

So far we tried to save the clipped image _with_ 
pantone background from photoshop. 

But it is also possible to save just the clipped 
part of the bitmap to pdf, with no background at 
all. And Lo! pdftex handles this correctly, overlaying
only the clipped object, leaving the clipped-out 
background intact. So the solution seems to be

> a) Do it with pdftex.
> Seems impossible because AFAIK pdftex supports neither 
> clipping paths nor masks.

I knew incorrectly. Clipped PDF works like a charm.

But now I have the next problem: How to underlay the 
special color? The named color model seems just the 
thing for me, but pdftex.def says

% Colour Support. The following models may be used.
%   * cmyk   supported directly.
%   * rgb    supported directly.
%   * RGB    converted to rgb by this file.
%   * gray   supported directly.
%   * named  converted to cmyk by this file.

which is exactly what I have to avoid by all means.

The PDF Specification is largely greek for me, but 
a [/Separation /PANTONE#<xyz> /DeviceCMYK <tintTransform>] 
or maybe a [/DeviceN ...] Color Space seems to be
just what I need.

I'm willing to do my best suggesting an extension to
pdftex.def for supporting additional color spaces,
but I need a little help getting started.

According to the pdf spec (1.3 section, for using
a color space which is not rgb, cmyk or gray, one would
need e.g. something like

/CS<xy> cs 
<tint> scn

assuming the resource dictionary contains something like

/CS<xy> [/Separation /PANTONE#<xyz> /DeviceCMYK <tintTransform>] 

But what is a resource dictionary and how to get something 
into it?

And does bychance anyone have the slightest idea what
<tintTransform> should look like (for, say, returning 
an appropriately lightened version of a CMYK approximation).


  Stephan Lehmke     		 Stephan.Lehmke at cs.uni-dortmund.de
  Fachbereich Informatik, LS I	 Tel. +49 231 755 6434 
  Universitaet Dortmund		 FAX 		  6555
  D-44221 Dortmund, Germany             

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