Portable Network Graphic, PNG is a lossless raster graphics format, primarily designed for displaying images on the internet or via digital delivery. This format supports transparency.
PNG8 uses a 2bit alpha channel to render transparency similar to GIF images. This means a pixel within the image is either opaque or transparent.
The PNG24 format utilizes an 8bit alpha channel allowing for varying amounts of opacity within a single pixel.
Animated PNG's were a proposal put forward for a format similar to
MNG, but simpler than
MNG and better quality than a
GIF, it was not taken forward, though animated PNG's are still used in some places. The reason they haven't been widely adopted is due to there being very little browser support for them.