Blocks by Hue and Brightness Where there is a perceptual hue difference between adjoining pixels – a perceptual difference is one where the colour name is different – or a brightness difference greater than the one specified, the output places an opaque pixel and, by option, continues this horizontally and/or vertically at a colour that is the mdian, most or lest saturated or light of those affected before another change takes place.
The effect is to produce a form of edge detection, without the fill-ins, or a set of colour blocks based on edge etection with the fill-ins.