1 Title: LZW Compression for Graphics Libraries in BLFS
3 Author: Michael A. Peters <mpeters@mac.com>
6 Adding LZW compression to graphics applications that can utilize it
18 3. Giflib as replacement for libungif
25 In the early 1980's a compression algorithm known as LZW emerged that
26 was very good at lossless compression of data. This algorithm was used
27 in a variety of software products, such as the UNIX compress command.
29 LZW was chosen as the compression algorithm for the CompuServe GIF image
30 format, as well as the TIFF image format. A free library emerged called
31 Giflib that allowed freeware and shareware authors to write programs for
32 the GIF image format, and as a result, the GIF image format became very
35 A company called Unisys existed that owned a patent on this algorithm,
36 but they did not complain until the GIF image format was already in very
37 wide use. At that point in time, they decided they wanted to charge a
38 very expensive licensing fee to use the LZW compression algorithm.
40 Since free software is free, this became a problem for the free software
41 industry. The result was that LZW was ripped out of several products.
43 This document tells you how to put it back in since many countries do
44 not recognize the Unisys software patent, and the patent is very close
45 to expiring in the U.S. if it has not expired already.
49 The PNG image format has largely replaced the GIF image in the free
50 software world. However, the evil was not with LZW - but rather, with
51 the software patent that restricted its use without licensing.
53 Since the compression algorithm itself is a very good one, there is no
54 reason not to use it where we can. Also, while PNG can be used as a
55 replacement for GIF, there is not really a suitable replacement for the
56 TIFF image format. Patching LZW support back into libtiff will allow the
57 creation of compressed TIFF images, and the compression makes a big
58 difference in the final file size.
62 In some countries it may not be legal to use the LZW algorithm without
63 paying a license fee. To the best of my knowledge the patent expires in
64 June 2003 in the United States. However, I believe the patent does not
65 expire in Japan until June 2004. You are advised to follow your local
66 law with respect to using the LZW compression algorithm and any license
67 fees that you are required to pay to do so. You are also advised to
68 look up the patent expiration date yourself, rather than rely on the
69 information I provide. I am not a patent lawyer.
71 3. Giflib as replacement for libungif
72 -------------------------------------
73 libungif was written as a replacement for Giflib. libungif does not use
74 LZW but instead produces uncompressed GIF images. If you would rather
75 produce compressed GIF images, then build Giflib instead of libungif.
77 Giflib 4.1.0 can be downloaded from:
78 http://ftp.rge.com/pub/multimedia/libungif/giflib-4.1.0.tar.gz
80 Follow the same build instructions for libungif in the BLFS book.
84 Most configure scripts will find libgif in your library path and use
85 that if you don't have libungif install. This is not universally true.
86 Some packages, such as emacs, will specifically look for libungif.
88 There are two ways to solve this issue. The first to make the following
89 symlinks in your /usr/lib directory:
90 ln -s libgif.a libungif.a
91 ln -s libgif.la libungif.la
92 ln -s libgif.so libungif.so
93 ln -s libgif.so.4 libungif.so.4
94 ln -s libgif.so.4.1.0 libungif.so.4.1.0
96 The second method, which is a little cleaner IMHO, is to modify the
97 configure scripts and Makefiles of the source to the software before
98 building it. For example, with emacs, there are two files that need
99 to be edited: configure and src/Makefile.in
101 In both files you just need to change every reference of lungif to lgif:
103 cp configure configure.orig &&
104 sed -e s?"ungif"?"gif"? < configure.orig > configure &&
106 cp Makefile.in Makefile.in.orig &&
107 sed -e s?"ungif"?"gif"? < Makefile.in.orig > Makefile.in &&
110 Then you can proceed to build as normal and emacs will use libgif.
114 To put LZW compression back into libtiff, all you need to do is apply
115 the LZW Compression Kit to the source before building it.
116 You can download the kit from:
117 ftp://ftp.remotesensing.org/libtiff/libtiff-lzw-compression-kit-1.3.tar.gz
119 The official instructions in the kit say:
120 "Just copy tif_lzw.c over the copy in libtiff and rebuild libtiff."
122 In other words, unpack the libtiff source as you would while following
123 the BLFS instructions. Before you do anything else, also unpack the
124 libtiff-lzw-compression-kit and replace the tif_lzw.c file in the
125 libtiff source directory with the one in the compression kit.
127 Then continue to build libtiff as described in the BLFS book.
131 Most applications that offer gif support will use libgif or libungif.
132 However, some applications will look for gif support in the gd library
133 and use gd for gif support if it finds it.
135 The author of the gd library no longer includes any gif support in his
136 library. However, we can patch gif support (with LZW compression) back
137 into gif so that software that wants to use gd for gif support can find
140 The gd library can be downloaded from:
141 http://www.boutell.com/gd/http/gd-2.0.12.tar.gz
143 The patch to the gd library can be downloaded from:
144 http://downloads.rhyme.com.au/gd/patch_gd2.0.12_gif_20030401.gz
147 patch -p1 < ../patch_gd2.0.12_gif_20030401 &&
148 ./configure --prefix=/usr &&
153 It is best to build gd after building zlib, libpng, freetype2, libjpeg,
154 and XFree86 - as gd will use those libraries if configure finds them.