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