PNG
Portable Network Graphics
PNG (Portable Network Graphics) - PNG is an extensible file format for the lossless, portable, well-compressed storage of raster images. PNG provides a patent-free replacement for GIF and can also replace many common uses of TIFF. Indexed-color, grayscale, and truecolor images are supported, plus an optional alpha channel for transparency. Sample depths range from 1 to 16 bits per component (up to 48bit images for RGB, or 64bit for RGBA). (72 visits)
http://www.w3.org/Graphics/PNG/
PNG transparency test - (131 visits)
http://entropymine.com/jason/testbed/pngtrans/