[gs-bugs] [Bug 688395] colors lost when converting PDF to TIFF

bugzilla-daemon at ghostscript.com bugzilla-daemon at ghostscript.com
Mon Jun 6 14:38:11 UTC 2011


Robin Watts <robin.watts at artifex.com> changed:

           What    |Removed                     |Added
                 CC|christinedelight.top85 at yaho |
                   |o.com                       |

--- Comment #19 from Robin Watts <robin.watts at artifex.com> 2011-06-06 14:38:08 UTC ---
>From quickly rereading the bug history, it sounds like these 'transparent'
areas are being generated by drawing a checkerboard pattern over certain areas.
This is a risky business as it relies on the file generators assumptions as to
exactly what pixels will be set by a given rendering operaton. This is tricky
to predict at best, and made intractably hard by having to support a range of
resolutions. Presumably these files have been 'designed' to work with just one
resolution and one known renderer.

This is a fault in the postscript file, and (as can be seen by the preceeding
comments) is not really something we can hope to cope with in all generality
within ghostscript.

It is possible that the new tiffscaled device may offer some help here,

If you have a desired output resolution where the default rendering gives the
"wrong" result, then by selecting a multiple of that resoluton, and using the
tiffscaled devices inbuilt downscaler, we can probably find a resolution where
it does work.

For instance:

 gs -r100 -sDEVICE=tiff2nc -o out.tif 191723000000.pdf

gives the wrong result.

 gs -r200 -sDEVICE=tiffscaled24 -dDownScaleFactor=2 -o out.tif 191723000000.pdf

however, will render at 200dpi, then scale down to 100dpi, and will give the
correct result.

Sadly, it's not enough to assume that all multiples will work:

 gs -r300 -sDEVICE=tiffscaled24 -dDownScaleFactor=3 -o out.tif 191723000000.pdf

doesn't work, but 400/4, 500/5 and 600/6 all do.

Does this count as enough of a workaround to be able to close this bug?

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