Methods and apparatus for defining contours in colored images

Apparatus for defining a contour in a coloured image to separate a selected region having a selected colour or colours from other regions wherein a colour component content of each pixel of said coloured image is defined by digital data at a first resolution, the apparatus comprising a first store for storing said digital data at said first resolution;

• and processing means for
• a) Defining at least one region of said coloured image containing colours which are to be located in said selected region;
• b) For each of said pixels in said defined region(s) deriving a digital colour component representation at a second resolution higher than said first resolution by combining said colour component content of one or more adjacent pixels with said colour content of said pixel;
• c) Designating each of said digital colour component representations at a second resolution derived in step b as a "selected colour value";
• and,
• d) Performing an edge following algorithm to define said contour within said coloured image including deriving said digital colour component representation at said second resolution for each of said pixels under consideration in the same manner as in step (b), determining whether each of said digital colour component representations at a second resolution is one of said selected colour values, and designating one of said pixels as lying on said contour by reference to the arrangement of neighbouring pixels having said selected colour values.