Generating a colour video signal representative of a stored picture

Colour video signals are generated representative of a stored picture, e.g. for use with an electronic tablet or graphics system, by reading from a code store (20) a succession of colour codes each indicating a pixel colour, looking up in a palette store (22) the colour component values corresponding to each colour code, and combining in an interpolator (30) two selected colour component values to provide an output. The combination function is determined by a circuit (32) on a pixel-by- pixel basis from control codes included in the sequence of codes stored in the code store (20). The interpolated colours may be not available on the palette, and if the interpolation is to improve the appearance of a colour transition, the position of the edge may be defined to a fraction of a pixel.