An apparatus for mapping a logical pixel value 2 defining pixel appearance to a plurality of physical appearance component values for driving a display device is described. Read addresses for a plurality of palettes 4, 6, 8 and 10 are derived from bits of the logical pixel value. The portions of the logical pixel value which are used to provide these read addresses overlap. Multiple storage of given physical appearance values GPV0, GPV1, . . . within the palettes is provided so as to ensure the appropriate output irrespective of what particular value a bit has that is non-significant for that palette. Three component color palettes 4, 6 and 8 addressed with 8-bit addresses are provided together with an effects palette 10 addressed by a 4-bit address. In the case of a 16-bit logical pixel value, the system has the flexibility to support any of 6-5-5, 5-6-5 or 5-5-6 depending upon what is stored within the color palettes.