A Massively Spiffy Yet Delicately Unobtrusive Compression Library
(Also Free, Not to Mention Unencumbered by Patents)

(Not Related to the Linux zlibc Compressing File-I/O Library)

Welcome to the zlib home page, created by Greg Roelofs and maintained by Jean-loup Gailly (on disk space provided by France Teaser). If this page seems suspiciously similar to the PNG Home Page, rest assured that the similarity is completely coincidental. No, really.

Current release:

zlib 1.2.1

Version 1.2.1 adds many improvements and features to zlib. Here are some highlights:

You can also look at the complete Change Log.

Versions 1.1.4 and later fix a potential security problem, see details here. Any software that is linked against or derived from an earlier version of zlib should be upgraded immediately. A partial list of over 500 applications using zlib is given here (uncompressed).

Canonical URL: http://www.gzip.org/zlib/

Mirror sites:

[DDJ's zlib image] zlib is designed to be a free, general-purpose, legally unencumbered -- that is, not covered by any patents -- lossless data-compression library for use on virtually any computer hardware and operating system. The zlib data format is itself portable across platforms. Unlike the LZW compression method used in Unix compress(1) and in the GIF image format, the compression method currently used in zlib essentially never expands the data. (LZW can double or triple the file size in extreme cases.) zlib's memory footprint is also independent of the input data and can be reduced, if necessary, at some cost in compression. A more precise, technical discussion of both points is available on another page.

zlib was written by Jean-loup Gailly (compression) and Mark Adler (decompression). Jean-loup is also the primary author/maintainer of gzip(1), the author of the comp.compression FAQ list and the former maintainer of Info-ZIP's Zip; Mark is also the author of gzip's and UnZip's main decompression routines and was the original author of Zip. Not surprisingly, the compression algorithm used in zlib is essentially the same as that in gzip and Zip, namely, the `deflate' method that originated in PKWARE's PKZIP 2.x.

Mark and Jean-loup can be reached by e-mail at zlib@gzip.org . Please read the FAQ and the manual before asking us for help. We are getting too many questions which already have an answer in the zlib documentation.

Greg, Mark and/or Jean-loup will add some more stuff here when they think of something to add. For now this page is mainly a pointer to zlib itself and to the official zlib and deflate documentation. Note that the specifications both achieved official Internet RFC status in May 1996, and zlib itself was adopted by JavaSoft in version 1.1 of the Java Development Kit (JDK), both as a raw class and as a component of the JAR archive format.

The lovely zlib-vise image above was provided courtesy of Bruce Gardner, art director of Dr. Dobb's Journal. It appears in Mark Nelson's article in the January 1997 issue (see below).

The current release is publicly available here:

 * zlib source code, version 1.2.1, tar.gz format (338k, MD5 checksum ef1cb003448b4a53517b8f25adb12452):

 * France (www.gzip.org)
 * US (www.zlib.net)

 * zlib source code, version 1.2.1, tar.bz2 format (278k, MD5 checksum 8106069990476a3c5187301465bd7a60):

 * France (www.gzip.org)
 * US (www.zlib.net)

 * zlib source code, version 1.2.1, zipfile format (405k, MD5 checksum 6619c21d42418d399d549aeec3f9401a):

 * France (www.gzip.org)
 * US (www.zlib.net)

 * zlib compiled DLL, version 1.2.1, zipfile format (74k, MD5 checksum db599409ae2f84441ebd052979568c99):

 * France (www.gzip.org)
 * US (www.zlib.net)

Versions 1.1.4 and later fixes a double-free bug which creates a potential security problem described here.

NOTE: zlib does not currently support window sizes of 256 bytes (windowBits == 8). A 512-byte window is the smallest the encoder can use. (Most applications use the default 32,768-byte window size for best compression.)

Note that zlib is an integral part of libpng and has been tested extensively as part of many PNG-supporting applications. Upcoming versions of gzip and UnZip will also use zlib.

Related Links

 * zlib Frequently Asked Questions
 * Zlib-announce mailing list
 * Zlib-devel mailing list
Please do not send questions or comments about zlib to this mailing list. Send those directly to the authors at zlib@gzip.org after checking the FAQ and the manual, of course.
 * zlib Manual
 * zlib Technical Details
 * zlib-Related Specifications
 * zlib's Deflate Algorithm
 * zlib License

 * unofficial (contributed) patches and binaries (not tested by zlib team)
includes patches and ports for Cygwin, Delphi 5, Palm OS, Win64, and WinCE; performance patches (match.asm for MASM 6.1, malloc optimization); and binaries for Win16, Win32, and WinCE

 * zlib for Linux, both shared and static plus headers (mostly version 1.1.3, RPM format, many architectures)
 * zlib for HP-UX 10.20 and 11.00 (version 1.1.3, shared library and headers)
(alternatively here: HP-UX 10.20 and HP-UX 11.00)
 * zlib for SGI Irix 6.x (version 1.1.4, shared library and headers)
 * zlib for Solaris (version 1.1.4)
 * zlib for Solaris (version 1.1.3 - use above link for 1.1.4 instead)
 * zlib for Digital Unix 4.0 (version 1.1.3)
 * zlib for SCO Open Server 5.0 (version 1.1.4)
 * zlib for BeOS R5 (version 1.1.3)
 * zlib for Mac OS X: zlib is already included as part of Mac OS X
 * zlib for Mac OS (version 1.1.3)
 * zlib for OS/2 (version 1.1.3, DLL and static version for emx 0.9c, 46k)
(click here if link breaks)
 * zlib for Palm Pilot (port of version 1.1.3, possibly based on old 1.0.4 port)
 * zlib for Newton OS (version 1.1.4)
 * zlib for Windows CE (port of version 1.1.3, 205k)
 * zlib for RIM BlackBerry
 * zlib for Windows 9x/NT/2000/XP/2003 (version 1.2.1, DLL version, plus related utilities)
 * zlib for Windows 9x/NT (version 1.1.4, DLL and static version)
 * zlib for NetWare (NLM for zlib 1.1.4)
 * Mark Nelson's ZlibTool article and Win32 source code for Dr. Dobb's Journal (January 1997)
 * zlib C++ wrapper for the gz* functions.
 * zlib 32-bit OCX and 16-bit DLL (Visual Basic interface, source code and binaries, 84k)
 * zlib 32-bit OCX (C++ source and binaries for use with Visual Basic 4.x or Delphi 2.0)
(unsupported VB5 binary also available)
 * zlib Pascal port (version 1.1.2, Pascal source, tested with Turbo Pascal 7.0 and Delphi 3.02)
(not tested by us, but looks complete and well-maintained)
 * zlib Delphi 5 interface (update of contrib/delphi2 files)
(includes compiled object files and corresponding C++ Builder 5 project files)
 * zlib Perl interface (source code; look for Compress-Zlib*.tar.gz)
 * zlib Python interface (online manual; part of the standard library as of Python 1.5)
 * zlib Tcl interface mkZiplib
 * zlib Java interface (see also JAR format)
 * zlib reimplementation in pure Java
(not tested by us, but looks like a good alternative to java.util.zip)
 * Mark Nelson's JavaZip article (with source code) for Dr. Dobb's Journal (December 1997)
 * Gilles Vollant's zlib-based mini-zip and mini-unzip
(see also Info-ZIP's UnZip, which optionally can be compiled with zlib)
 * Scott Ludwig's zlib-based CExe executable compressor for Win32
 * Gilbert Baumann's inflate implementation in Common Lisp
(file src/net/deflate.lisp in Closure source archive)

 * zlib technical issues, including spec errors
 * zlib information in Japanese
 * Real World Scanning and Halftones (second edition includes a section on zlib)

 * Markus Oberhumer's LZO `real-time' data compression library
(not tested by us, but looks like a good alternative if you need more speed and less compression)
 * libbzip2
(not tested by us, but looks like a good alternative if you need more compression and less speed)
 * PPP Deflate Protocol (RFC 1979)
 * Info-ZIP Home Page
 * Portable Network Graphics (PNG) Home Page
 * gzip Home Page
 * DataCompression.info
 * comp.compression Frequently Asked Questions list

Send comments or questions about zlib to the authors at zlib@gzip.org  after checking FAQ and manual.
Please report broken links to jloup@gzip.org (PGP key). Last updated November 23rd, 2003.

Web page copyright © 1996-2003 Greg Roelofs, Jean-loup Gailly and Mark Adler.
zlib software copyright © 1995-2003 Jean-loup Gailly and Mark Adler.
Primary site hosted by France Teaser.
zlib.org domain name donated by Andrew Green.