Описание тега png-8
PNG8 (or png-8) is a subset of possible png files. PNG8 files are indexed PNG files with either no transparency or only binary (GIF-style) transparency in which all pixels are either fully opaque or fully transparent.
PNG8 (or png-8) is a subset of possible png files. PNG8 files are indexed PNG files with either no transparency or only binary (GIF-style) transparency in which all pixels are either fully opaque or fully transparent.
ImageMagick ( http://www.imagemagick.org),
GraphicsMagick ( http://www.graphicsmagick.org), and
define PNG8 as 8-bit indexed PNG with optional binary transparency.
Some people use "png-8" to mean 8-bit indexed files with all 256 levels of transparency allowed, but those could simply be called "indexed" PNGs. The libpng FAQ, ( http://www.libpng.org/pub/png/pngfaq.html#png8-png24) doesn't mention transparency in its discussion of PNG8.