OptiPNG Home Page

OptiPNG is a PNG optimizer that recompresses the image files to a smaller size, without losing any information.
The idea behind this program has been inspired from pngcrush (http://pmt.sourceforge.net/pngcrush), and is explained in detail in the PNG-Tech article "A guide to PNG optimization".

OptiPNG is still at an early version: 0.4.3 (released 12 Aug 2003). However, it already provides advanced optimization and error recovery features. Compared to pngcrush, OptiPNG has a wider automatic search space (which may lead to a better compression factor), and it runs faster.

The program can be downloaded in source code form: optipng-0.4.3.tar.gz, optipng-0.4.3.zip,
and in Win32 executable form: optipng-0.4.3-exe.zip.
The source code requires a recent version of libpng (the 1.0.X series works), and zlib version 1.1.4 or newer. For more information, please read the NOTE below.

The documentation is included in the downloadable archives, and it is also available here:

• LICENSE
  OptiPNG is open-source software, released under the zlib/libpng license.
• FEATURES
  The complete list of features.
• USAGE
  Program usage.
• CAVEAT
  We cannot, in good conscience, fail to inform the users about the known bugs, problems, or limitations. Caveat Emptore!
• DESIGN
  Internal documentation: design decisions and rationale.
• HISTORY
  The program revision history.
• TODO
  The "to-do" list.

NOTE:
The OptiPNG source distribution contains customized versions of zlib-1.1.4 (at http://www.zlib.org/) and libpng-1.0.15 (at http://www.libpng.org/pub/png/libpng.html)

• The constant TOO_FAR in zlib is set to 32768, for a slight compression improvement; see the PNG-Tech article "TOO_FAR in zlib is not too far...".
• Although the program is designed to work with any recent version of libpng (post- 1.0.6), we distribute a special version that contains a few minor corrections and improvements.

OptiPNG Plus

OptiPNG Plus is an enhanced version that provides additional features. This version is not publicly available.