Apparatus is provided to color-suppress a source frame that is composed of a plurality of pixels, each pixel being represented by three components defining a position within a color space. The source frame, comprising a foreground image against a background of a substantially uniform backing color, is provided to a processing means via an input means. A distance value is defined that for any, pixel describes how close its color is to a specified color, and the processing means calculates a transformation that maximises the distance value of a selected background pixel. Then, for each pixel, the processing means calculates a transparency value that is a function of the distance value of the corresponding transformed pixel. The transparency value is used to calculate how much of the backing color should be subtracted. The foreground image can then be composited with a replacement background using the same transparency values.