[cairo] Too-large transparency groups

James Cloos cloos at jhcloos.com
Thu Jun 20 11:45:13 PDT 2013

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

AJ> The PS output blends alpha into white if there is nothing underneath.
AJ> The PDF output preserves the alpha. PDF viewers blend the rasterized
AJ> image into the page color.

Given that cups-filters cause apps to prefer sending pdf to cups, even
when the printer is PS-only, and that pdftops and pdf2ps both raster the
whole page and not just the small image, that leaves the bug in place.

Tested with cairo master, poppler master, gs 9.07.

The reply I got elsewhere, pointing at cairo, was not current.  The
SMask is indeed the same size as the image.

But pdftocairo is the only Free Software pdf to ps converter which
avoids rasterizing the whole page.  But since it is limited to sRGB,
it is not suitable for use in a print stream filter, where colour spaces
must be passed through as is.

Obviously the bugs are in poppler, gs (and probably also in xpdf), in
their pdf to ps conversions.  But perhaps a work-around in cairo is not

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

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