[poppler] Proper Transparency Support in pdftops

[James Cloos]

>>>>> "AJ" == Adrian Johnson <ajohnson at redneon.com> writes:

AJ> Cairo PS output will only rasterize the regions that use transparency.
AJ> You can try "pdftocairo -ps" to see if it solves your problem.

Cairo won't be truly suitable for a print workflow until it has proper
colourspace support.  Squeezing, eg, a cmyk pdf to srgb to print on a
colour-managed ps printer is harmful.

In addition to minimizing rasterization a la cairo, there are a couple
of other tricks which would help.  In many cases it would be good enough
to approximate transparency by just multiplying the colourants by alpha.
That isn't true transparency, of course, but is enough for many files
which use argb or acmyk purely for convenience.

Longer term, both poppler and cairo could benefit from rasterizing to a
shading rather than to a pixmap.  OpenGL apps likely have suitable
algorithms for rasterizing to triangles which p & c could borrow.
Rasterizing to a tensor product shading, though, should be able to
replicate anything pdf can do without loss of precision.

Ghostscript's ps2writer also has unfortunate limitations.  Notably,
since it only targets level2 ps, it converts CIDFonts to bitmap
type 3 fonts¹.

1] from a comment posted today to gs-devel or to their bugzilla 

-JimC
-- 
James Cloos <cloos at jhcloos.com>         OpenPGP: 1024D/ED7DAEA6