it's called Run Length Encodingalthough it's possible to RLE optimize your image in a very lossy way so that near duplicatable colours are made identical,
however unlike the squares that appear in wavelet compression (jpeg), this optimization loss is highly noticable
(,
Sun 30 Jan 2005, 23:25,
archived)
however unlike the squares that appear in wavelet compression (jpeg), this optimization loss is highly noticable