Hi,
On 2014-10-08 12:23, Jakub Wilk wrote:
The splash backend uses bilinear interpolation for rendering images,
even when the image lacks the Interpolate flag. This seems to be
contrary to what PDF Reference 1.7 says:
When the resolution of a source image is significantly lower than
that of the output device, each source sample covers many device
pixels. As a result, images can appear jaggy or blocky. These visual
artifacts can be reduced by applying an image interpolation algorithm
during rendering. Instead of painting all pixels covered by a source
sample with the same color, image interpolation attempts to produce a
smooth transition between adjacent sample values. Image interpolation
is enabled by setting the Interpolate entry in the image dictionary to
true. It is disabled by default because it may increase the time
required to render the image.
Note: The interpolation algorithm is implementation-dependent and is
not specified by PDF. Image interpolation may not always be performed
for some classes of images or on some output devices.
I've attached a test PDF and two pdftoppm outputs that illustrate the
problem:
- with poppler 0.18.4, you get black&white image, as expected;
- with poppler 0.26.5, you get gray goo instead.
See also bug #760396 for some background information.
From a quick look, it seems like
https://bugs.freedesktop.org/show_bug.cgi?id=68360
could be your case.
If not, can you please report the findings in #760396 (with links, etc)
to a new bug in the upstream bug tracker?
Suggestions as to how I could work around this bug in pdf2djvu are
welcome.
I'm not sure you can do anything without changes in Poppler.
Thanks for your report,
--
Pino Toscano
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