[cairo] Use /Interpolate for PS?

[Adrian Johnson]

Chris Wilson wrote:
> Working through my pedagogical PS interpreter, I spotted that we do not
> specify the /Interpolate flag for images (PLR p301). Is there a reason
> why we leave it at the default value (off)? The PLR says that the
> default is off as it may increase the time to render, and that the
> actual algorithm is undefined... 

Carl noticed that we were not setting the /Interpolate flag shortly 
before 1.6 was released. I wrote a patch[1] to fix this however there 
were some issues. Ghostscript, acroread, and poppler did not render the 
filter-bilinear-extents test the same. Carl suggested we revisit this 
after 1.6 but I never did get around to finishing it.

[1] 
http://gitweb.freedesktop.org/?p=users/ajohnson/cairo.git;a=shortlog;h=image-interpolation