pngrewrite

Pngrewrite is command-line utility that reduces the unnecessarily large palettes that too many programs write into PNG files. It also optimizes transparency settings, and reduces the bits-per-pixel if possible. Handy for post-processing images before putting them on a web site.

It can probably run on most any platform on which libpng can run. A Windows version is included. For other platforms, you'll have to compile it yourself.

Download:

• pngrewrite v1.3.0 - 7 Dec 2008; 105KB
  (includes C source code, and a Win32 executable)

Read the comments at the beginning of the source code (pngrewrite.c) for more details.

• v1.3.0 - 7 Dec 2008
  • Cleaned up the code somewhat. No more global variables.
  • Improved error reporting.
  • Disabled "one argument" mode, where the first argument may be taken as the output file if standard-input is not a terminal. On consideration, I think there's too much of a risk of overwriting files by accident. It can be re-enabled at compile time. Otherwise, for piped I/O, use "-" as the file name.
  • Updated libpng in the included pngrewrite.exe file to v1.2.33.
• v1.2.1 - 9 Feb 2003
  • Fixed a bug in v1.2.0, which could occasionally cause the some pixels at the upper left to be the wrong color.
• v1.2.0 - 14 Jun 2002
• v1.1.1 - 11 Jun 2002
• v1.1 - 27 Apr 2002
• v1.0 - 25 Jan 2000