Package: libpoppler46 Version: 0.26.5-1 Control: block 760396 with -1
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.Suggestions as to how I could work around this bug in pdf2djvu are welcome.
-- System Information: Debian Release: jessie/sid Architecture: i386 (x86_64) Foreign Architectures: amd64 Kernel: Linux 3.16-2-amd64 (SMP w/2 CPU cores) Locale: LANG=C, LC_CTYPE=pl_PL.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Versions of packages libpoppler46 depends on: ii libc6 2.19-11 ii libfontconfig1 2.11.0-6.1 ii libfreetype6 2.5.2-2 ii libgcc1 1:4.9.1-16 ii libjpeg62 1:1.3.1-6 ii liblcms2-2 2.6-3+b1 ii libopenjpeg5 1:1.5.2-3 ii libpng12-0 1.2.50-2 ii libstdc++6 4.9.1-16 ii libtiff5 4.0.3-10+b1 ii multiarch-support 2.19-11 -- Jakub Wilk
test-interpolation.pdf
Description: Adobe PDF document
