The attached file, Bug687295a.pdf, is rendered differently with and without -dGraphicsAlphaBits=4 by Ghostscript. Acrobat X 10.1.1 agrees with the rendering of the file without the -dGraphicsAlphaBits=4 option. The command line I'm using for testing: bin/gs -sDEVICE=ppmraw -o test.ppm -dGraphicsAlphaBits=4 ./Bug687295a.pdf This is a regression, Ghostscript 9.02 renders the file the correctly with -dGraphicsAlphaBits=4; I've bisecting now.
Looks like this broke in: commit 8170bf69742a320e7e28bffa58cbf0f0f14f2eb0 Author: Michael Vrhel <michael.vrhel@artifex.com> Date: Thu Apr 7 03:30:16 2011 +0000 Fix for 692123. It was necessary to make sure that the blending state of the pdf14 device is updated when we have the alpha buffer git-svn-id: http://svn.ghostscript.com/ghostscript/trunk@12373 a1074d23-0009-0410-80fe-cf8c14f379e6
Looks like yet another hiccup in pdf14_copy_alpha.
Issue is that we are not paying attention to the knock out setting when performing copy_alpha in the pdf14 device. Working on a fix for this now.
Fixed with http://git.ghostscript.com/?p=ghostpdl.git;a=commit;h=a7b85f9823b1a1dea1530716a3e2fb3dd2f75c9c