The procedure aims at identifying, extracting and classifying visually important features on the image plane, such as regions of homogeneous colour and chromatic transitions. Well established principles of colour theory and graph theory are combined to obtain a unified representation of a colour picture. The picture is represented by means of a weighted graph, constructed so as to reflect the specification of the colour space employed as well as important relationships between picture elements. A spanning tree of the graph is obtained by iteratively minimising a specific picture distortion measure. Each partition comprises disjoint regions containing elements with similar attributes. Region contours defined by such partitions form a hierarchy. It is shown that, when texture is combined with colour as joint similarity attributes of regions, an improved hierarchical description of contours is possible.<<ETX>>