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GPL Ghostscript for Debian ========================== Links against shared JPEG library --------------------------------- On Debian systems, ghostscript is linked against the shared IJG JPEG library, instead of using the patched local copy bundled with the ghostscript source. The two versions of the library behave identically except in two respects, both concerning invalid JPEG streams: - The bundled libjpeg fakes a valid component id when JPEG streams include an SOF or SOS marker whose component identifiers are not all distinct (see the description of C_i in B.2.2 of the JPEG spec). The shared IJG JPEG library produces artifacts (e.g., stripes) when presented with such component ids. https://bugs.ghostscript.com/show_bug.cgi?id=686980 - The bundled libjpeg is configured to accept up to 64 blocks per MCU, instead of the limit of 10 blocks per MCU described in the Postscript reference manual and JPEG standard. According to lore and Adobe's tech note 5116, in 1991 Adobe came across some files in the wild exceeding the standard for blocks per MCU, and Adobe's implementation would sometimes accept such streams. That said, the PRLM3 states quite straightforwardly that the number of blocks in the MCU must not exceed 10. The PRLM2 contains the same condition, but attributes it to "the JPEG-proposed standard". Thus, we believe that any PostScript file containing this kind of JPEG stream can safely be considered invalid. If you come across a file triggering either of these conditions, please let us know by reporting a bug against the ghostscript package. See Bug #582522 and Bug #582521 for more detail, particularly https://bugs.debian.org/582522#46 Links against shared OpenJPEG library ------------------------------------- The GPL Ghostscript project maintains a fork of OpenJPEG with a set of patches applied related to color calibration of JPEG2000 data: https://git.ghostscript.com/?p=ghostpdl.git;a=commitdiff;h=ef8503 On Debian systems, ghostscript is linked against mainline OpenJPEG which do not (at least for versions 1.3+dfsg-4.7 and 1.5.1-1) include those patches. DroidSansFallback is default fallback for CJK documents ------------------------------------------------------- GPL Ghostscript uses the DroidSansFallback font from the fonts-droid package to substitute for CID-keyed fonts that are not available (used for East Asian character sets in PDFs). If disk space is scarce, remove the fonts-droid package and the glyphs from missing fonts will be rendered as bullets. See Use.htm#CIDFontSubstitution from the ghostscript-doc package for details. -- Jonas Smedegaard <dr@jones.dk> Thu, 04 Jul 2013 03:46:38 +0200