PNG Image Crushers
This article lists tools for optimising/compressing PNG files. This can be useful for reducing PNG file sizes for use on devices with only a small amount of memory.
Pngcrush is an optimizer for PNG (Portable Network Graphics) files. It can be run from a commandline in an MSDOS window, or from a UNIX or LINUX commandline.Its main purpose is to reduce the size of the PNG IDAT datastream by trying various compression levels an PNG filter methods. It also can be used to remove unwanted ancillary chunks, or to add certain chunks including gAMA, tRNS, iCCP, and textual chunks.
OptiPNG Advanced PNG Optimizer 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. It is based on Pngcrush
PNGOUT is a tool which can optimize PNG files created by other programs. It can be run from the Windows Run dialog box or at the command prompt. PNGOUT can produce even smaller files than pngcrush -brute or optipng -o7, however, since PNGOUT does not automate trials, you will have to find the right options yourself. PNGOUT Tutorial