1. An image mapping system comprising: an input arranged to receive at least part of an input image of a first bit-depth; a processor arranged to compute statistics describing the input image and to fit a multi-modal model to the statistics; the processor also being arranged to determine a multi-modal tone-mapping function using the multi-modal model; and a tone-mapping processor arranged to apply the tone-mapping function to the received input image to form an output image of bit-depth different from the input image.