Displacement explained

Puzzled over how the filter behaves? It’s all about brightness values... The Displace filter shifts pixels up or down and left or right based on the brightness of the displacement map, in order to approximate a 3D surface. The horizontal and vertical values (H and V) [1] can go to +/-999, although you rarely need to go above 50. The diagram here shows how this pixel-shifting works. The centre circle [2] is unchanged. In the top left [3] , both H and V are set to a positive value. Areas of the shape that sit over the brighter parts of the displacement map are pushed upwards and to the left, while dark areas shift down and to the right. Set both to negative values [4] and the brighter areas shift down and to the right. If you set H positive, V negative [5] then brighter parts shift down and to the left; while H negative, V positive [6] pushes them up and to the right.