Radial grad posterized with polar coordinates used both ways

If you posterize a coloured gradient and keep the level of posterization fairly low you get an effect like the square above - i.e. bands of solid colour. These form a good basis for 'distortion' filters - in this case the 'polar coordinate' which has been used one way to create the curved shapes and the other that has produced the background arches. Poster edges have been used to sharpen up the appearance.