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[libpng16] Revised manual about handling of zlib CMF

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Glenn Randers-Pehrson 2013-11-24 13:33:07 -06:00
parent d56af331e1
commit 30145f29c5
2 changed files with 16 additions and 14 deletions
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15
libpng-manual.txt
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@ -5051,18 +5051,19 @@ The machine-generated configure files are no longer included in branches
libpng16 and later of the GIT repository. They continue to be included
in the tarball releases, however.
Libpng-1.6.0 and later use the CMF bytes at the beginning of the IDAT stream
to set the size of the sliding window for reading instead of using the default
32-kbyte sliding window size. It was discovered that there are hundreds of PNG
files in the wild that have incorrect CMF bytes that cause libpng to now issue
a "too far back" error and reject the file. Libpng-1.6.3 provides a way to
revert to the libpng-1.5.x behavior (ignoring the CMF bytes and using a
Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
stream to set the size of the sliding window for reading instead of using the
default 32-kbyte sliding window size. It was discovered that there are
hundreds of PNG files in the wild that have incorrect CMF bytes that caused
libpng to issue a "too far back" error and reject the file. Libpng-1.6.3 and
later calculate their own safe CMF from the image dimensions, provide a way
to revert to the libpng-1.5.x behavior (ignoring the CMF bytes and using a
32-kbyte sliding window), by using
png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
PNG_OPTION_ON);
and provides a tool (contrib/tools/pngfix) for optimizing the CMF bytes
and provide a tool (contrib/tools/pngfix) for optimizing the CMF bytes
correctly.
Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong

15
libpng.3
View File

@ -5556,18 +5556,19 @@ The machine-generated configure files are no longer included in branches
libpng16 and later of the GIT repository. They continue to be included
in the tarball releases, however.
Libpng-1.6.0 and later use the CMF bytes at the beginning of the IDAT stream
to set the size of the sliding window for reading instead of using the default
32-kbyte sliding window size. It was discovered that there are hundreds of PNG
files in the wild that have incorrect CMF bytes that cause libpng to now issue
a "too far back" error and reject the file. Libpng-1.6.3 provides a way to
revert to the libpng-1.5.x behavior (ignoring the CMF bytes and using a
Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
stream to set the size of the sliding window for reading instead of using the
default 32-kbyte sliding window size. It was discovered that there are
hundreds of PNG files in the wild that have incorrect CMF bytes that caused
libpng to issue a "too far back" error and reject the file. Libpng-1.6.3 and
later calculate their own safe CMF from the image dimensions, provide a way
to revert to the libpng-1.5.x behavior (ignoring the CMF bytes and using a
32-kbyte sliding window), by using
png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
PNG_OPTION_ON);
and provides a tool (contrib/tools/pngfix) for optimizing the CMF bytes
and provide a tool (contrib/tools/pngfix) for optimizing the CMF bytes
correctly.
Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong