PNG: Portable Network Graphics Format
Introduced in 1995 as a free alternative to Unisys's greedy patent claim on the GIF format, PNG was slow to be adopted by companies like Microsoft so the format did not catch on right away. Today PNG is supported by all the major web browsers. PNG builds on the idea of transparency in GIF images and allows the control of the degree of transparency, known as opacity. PNG uses deflate compression and is sometimes preprocessed in a way that helps it compress better. PNG does not support animation like GIF does.
A PNG stream consists of a number of data chunks. Each chunk stores its type and size, then follows the chunk data, then a CRC-32 checksum value. PNG image types are Grayscale, with 1, 2, 4, 8 or 16 bits per sample, RGB truecolor, with 24 or 48 bits per pixel, Paletted, with 1, 2, 4 or 8 bits per pixel. Like GIF, the PNG format supports transparency. Howevever, unlike GIF, PNG can do it on truecolor images. Both grayscale and truecolor can store an alpha channel which contains transparency information.