PNG (Portable Network Graphic)
PNG is a patent-free computer data format that uses lossless compression specifically designed for raster images. It was created in order to replace older propriety graphics
formats like GIF.
PNG stands for "portable network graphic" and is pronounced "ping". The original PNG specifications were published on July 1st, 1996. The major reason for the creation of
the PNG standard was when Unisys announced that they would start enforcing their patent on the LZW data compression algorithm which is used in GIF. This meant that any program
that would save images in GIF format would have to pay royalties to Unisys. PNG, however, is completely patent-free, and out performs the GIF format in several ways.
PNG's specifications are quite impressive. The PNG format allows paletted 8 bit color, 24 bit color, 48 bit color, and 16 bit grayscale. PNG also allows up to 8 bit alpha
transparency. PNG uses a variant of the LZ77 compression algorithm similar to the type that is used in the Zip compression format. PNG also allows
for automatic gamma correction on cross-platform viewing. PNG allows for 2-D interlacing, has three built integrity checks, and has built-in support for image mapping.
The PNG graphic format also successfully replaces older graphic formats like Microsoft's BMP, ZSoft's PCX, and in many cases, TIFF.
PNG isn't without its share of problems. There are still many Internet browsers that don't fully support PNG's alpha transparency. Also, the full capability of PNG's
compression isn't always properly implemented causing the file size to be too large. PNG doesn't support animation like the GIF format, however PNG's sister format, MNG does.
libpng.org - The PNG committee's official site.
entropymine.com/jason/testbed/pngtrans - Browser test for PNG's alpha transparency.