OptiPNG is a tiny command line tool which optimises PNG files, often reducing their size but without affecting image quality.
Our tests showed varying results. OptiPNG barely made any difference at all with some files, occasionally cutting others by 20% or more, but on average saved around 5%.
Using the program can be as simple as entering something like:
OptiPNG then tries various parameters to find which delivers the smallest file size. But beware, if there are savings to be made then it overwrites the original file.
If you'd prefer to keep the source file, use:
optipng -keep image.png
It'll be preserved as image.png.bak.
Multiple images may be specified on the same command line:
optipng -keep image1.png image2.png image3.png
There are various other options to control the compression strategy, how and where any saved files are written. Enter optipng -h to find out more.
If you'd prefer a GUI, note that PNGGauntlet provides a shell for OptiPNG, and adds a couple of other tools to deliver even greater savings.
* Upgraded libpng to version 1.6.21.
! Fixed an assertion failure in the image reduction code.
[Fixed by upgrading libpng]
!! Fixed various security-sensitive defects in the BMP decoder.
[Reported by Henri Salo and Hans Jerry Illikainen]
[Fixed by Ramona C. Truta]
! Fixed a benign uninitialized memory read in the GIF decoder.
[Fixed by cherry-picking from the original gifread code]
! Fixed a build failure occurring under the Estonian (et_EE) locale.
[Reported by Sebastian Pipping]
[Fixed by Priit Laes]
! Fixed a build failure occurring on Mac OS X, FreeBSD, and possibly
other systems that lack POSIX-compliant high-resolution timestamps.
[Reported by Ryan Schmidt and Dmitry Egorov]
[Contributed by Sebastian Pipping]
! Fixed a typo causing build failures in 32-bit ANSI C compilation.
[Reported by various users]
A powerful PNG optimizer, easy to use (by command line standards) but with plenty of low-level control for experts.