Palette Master is an obscure paint program for the Atari ST, developed by Kevin Cowtan. It uses palette switching to display more than 16 colors at a time. It has a native .ART image format.
The files are exactly 36864 bytes in length and consists of two areas. First is the picture area, which is 32768 bytes long. Second is the palette area, which is 4096 bytes long. All numbers are in big-endian format.
The picture is stored in television order with no gaps between scanlines, and is always 320x200. Each 16x1 area of pixels is stored as four 16-bit words, where the high-bit of each 16-bit word corresponds to the left pixel; each 16-bit word is one plane, where the low plane comes first. (Note: There are 768 unused bytes at the end of the picture.)
The palette area stores the palettes. The first one stores sixteen colours in the format described for Atari ST color palette. The others are the same except that colour index 0 is not stored (it is the same for the entire picture); instead, the first 16-bit number is the (zero-based) scanline number to start using this palette (it is then used until it is changed again). They are stored in monotonic increasing order by scanline number; at the end, scanline number -1 (or 65535) means there are no more palettes.