mat jpeg or tiff) by its colour. It uses a simple form of the
technique known as Support Vector Machine, adapted to this particular
problem. The original colour variables (<code>R, G, B</code>) are transformed into
colour proportions (<code>r, g, b</code>), and the resulting two dimensional plane,
defined by any convenient pair of the transformed variables is divided in
several subsets (categories) by one or more straight lines (rules) selected
by the user. Finally, the pixels belonging to each category are