OptiPNG: Advanced PNG Optimizer

OptiPNG is a PNG optimizer that recompresses image files to a smaller size, without losing any information. This program also converts external formats (BMP, GIF, PNM and TIFF) to optimized PNG, and performs PNG integrity checks and corrections.
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.

Latest version: OptiPNG 0.5.5 (released on 28 January 2007).

Download

• Go to the OptiPNG download page at SourceForge.
• Follow the direct links to the latest version.

  The source code tarball:	optipng-0.5.5.tar.gz
  The source code zip archive:	optipng-0.5.5.zip
  The Windows executable:	optipng-0.5.5-exe.zip

Documentation

The documentation is also included in the downloadable archives.

• LICENSE
  OptiPNG is open-source software, released under the zlib/libpng license.
• FEATURES
  The complete list of features.
• HISTORY
  The program revision history.
• CAVEAT
  We cannot, in good conscience, fail to inform the users about the known bugs, problems, or limitations. Caveat Emptor!
• DESIGN
  Internal documentation: design decisions and rationale, mainly addressed to potential contributors.
• TODO
  The "to-do" list.
• THANKS!
  The author is indebted to all the people who helped the OptiPNG development.

Unix security note

The OptiPNG source distribution contains modified versions of zlib-1.2.3 and libpng-1.2.15, but the program works with the original libraries as well. These libraries are available at their home sites. (Comments and complaints about these modified libraries should be addressed to the OptiPNG author, not to the authors or to the maintainers of the original libraries.)

• zlib at http://www.zlib.net/
  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
  The original library provides functionality beyond what's needed by OptiPNG. The modified version has the unused functionality disabled and compiled out, allowing a smaller executable.

We are, of course, greatly concerned with the correctness of this program (running on all platforms, not just on Unix!), and all the code and the supporting libraries have been extensively tested. However, some Unix package maintainers and system administrators prefer to link the code to the system-supplied zlib and libpng, which are constantly updated with the latest and greatest versions and security patches.

We are, therefore, offering the possibility to build the program such that it uses the system-supplied libraries. Should you wish to do so, please use the unix-secure.mak makefile. Be aware that, by not using the bundled (and tailored) zlib, you will lose a tiny fraction of the compression ratio.

OptiPNG-related utilities

• akJ OptiPNG Wrapper, available at http://www.xucker.jpn.org/eclipsercp/optipngwrapper/, is an Eclipse RCP (Rich Client Platform) application.
  More related utilities are available in Japanese, at http://www.xucker.jpn.org/keyword/optipng.html.
• PNGCrusher, available at http://www.amake.us/software/pngcrusher/, is a frontend for Mac OS X, that also includes an OS X-compiled OptiPNG binary.
  In spite of the similar name, this program is different than pngcrush. The name similarity is due to the fact that PNGCrusher was originally based on pngcrush.