Creates large, flat areas of colour or tone in your images.
Apply this adjustment via the Adjustment button on the Layers panel or via Layer > New Adjustment.
The following settings can be adjusted in the dialog:
Posterise Levels—controls the number of coloured areas produced and the complexity of the resulting image. Drag the slider to the left to decrease the number of coloured areas (thereby simplifying image layout), drag to the right to increase coloured areas (thereby giving a more complex image layout).