Pngout edit
Please, don't shout while making blatantly false claims. "This file is already compressed fully using PNGout. As of now, there is no smaller filesize possible." -- except that PNGout is pretty weak. It is also non-free and often corrupts images.
From my personal tests, you can get best results by using optipng then advancecomp -- the former has good optimizations of IDAT, the latter does deflate well.
In this case, optipng even in non-aggressive settings can beat PNGout by over 0.6% (quite a bit while not being allowed to change the file format). --KiloByte (talk) 22:10, 17 October 2011 (UTC)
