From: Bob Friesenhahn <bfriesen@si...> - 2004-09-18 00:55:45
For many years, libtiff has not included LZW support due to patent
issues. The LZW support for libtiff has been made available as a
replacement source file. As of GraphicsMagick 1.1.3, LZW is now
enabled by default. When LZW is enabled in GraphicsMagick, it will
attempt to use LZW in libtiff since there seems to be no good way to
know if the installed libtiff supports LZW compression.
If a TIFF file is written requesting LZW compression and libtiff
doesn't support it, a warning is issued and the output file is junk.
This is particularly dangerous with the 'mogrify' command since it
replaces the input file. The image provided to 'mogrify' may be
If you are using TIFF, please make sure that either libtiff includes
LZW compression, or LZW is disabled entirely in GraphicsMagick. When
in doubt, use the 'convert' command instead. With the 'convert'
command, you can verify that the output file is ok before replacing
the input file.