OptiPNG: Advanced PNG Optimizer

Current version: OptiPNG 0.4.5 (released 31 May 2004)
Download the source code: optipng-0.4.5.tar.gz, optipng-0.4.5.zip
Download the Windows executable: optipng-0.4.5-exe.zip

OptiPNG is a PNG optimizer that recompresses the image files to a smaller size, without losing any information.
The idea 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". The implementation is carried forward in OptiPNG, which offers a faster execution per trial, and a wider search space.

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 modified versions of zlib-1.2.1 and libpng-1.0.15. The original libraries are available at their home sites:

• zlib at http://www.zlib.org/
  (A notable change: the constant TOO_FAR is set to 32768, for a slight compression improvement; see the PNG-Tech article "TOO_FAR in zlib is not too far...".)
• libpng at http://www.libpng.org/pub/png/libpng.html
  (Although OptiPNG is designed to work with any recent version of libpng (post- 1.0.6), we distribute a special version that contains some corrections and improvements.)

OptiPNG Plus

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