http://studio.imagemagick.org/pipermail/magick-developers/2008-July/002997.html
the -flatten option is necessary starting from IM 6.3.5
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@25762
a592a061-630c-0410-9148-
cb99ea01b6c8
opts = '-define pdf:use-cropbox=true ' + opts
# If supported, add the -flatten option for ppm target formats (see bug 4749)
-if sys.argv[2][:4] == 'ppm:' and version >= 0x060000:
+if sys.argv[2][:4] == 'ppm:' and version >= 0x060305:
opts = opts + ' -flatten'
if os.system(r'convert %s "%s" "%s"' % (opts, sys.argv[1], sys.argv[2])) != 0: