pngout is a program that optimizes the size of a PNG file using a lossless algorithm to make their sizes more friendly for use on the web. To install it, go to the pngout Linux/Mac OS X port page for the program:
Click on the Dynamic download link under Linux, since FC6 uses a glibc version that is greater than 2.3.5. This will download the current version, which at the time of this writing, is pngout-20070110-linux.tar.gz. Once downloaded, create an appropriate directory to install pngout under /usr/local/src/pngout:
~> sudo mkdir -p /usr/local/src/pngout/pngout-20070110
Move the tarball to the directory: ~> sudo mv ~/Desktop/pngout-20070110-linux.tar.gz /usr/local/src/pngout/pngout-20070110.
Change into the pngout/pngout-20070110 directory: ~> cd /usr/local/src/pngout/pngout-20070110
and decompress the tarball: ~> sudo tar vfzx pngout-20070110-linux.tar.gz
Once the package has been decompressed, delete the tarball: ~> sudo rm pngout-20070110-linux.tar.gz
You should notice that pngout has already been
compiled, and what was decompressed by the tarball is several binary
files. The file we are interested in is pngout-i686. To use it, create a soft link from /usr/local/bin to its location: ~> sudo ln -s /usr/local/src/pngout/pngout-20070110/pngout-i686 /usr/local/bin/pngout
Finally, source the ~/.tcshrc file: ~> source ~/.tcshrc
If you need help with the syntax, type: ~> pngout --help
I've found the program works well, and have used it to compress a number of images that are used on this website.