Physics-based colour image segmentation for scenes containing vegetation and soil

Colour segmentation of images containing vegetation and soil is the theme of this work. Physics-based reflection models are used to develop an algorithm for separating object pixel clusters in the three-dimensional red, green and blue colour space. The dichromatic reflection model that is used as the basis for this algorithm, defines a plane in which the pixels from an object of a given colour will lie. The illuminant colour and the intrinsic body colour of the object determine the parameters of the dichromatic plane. Scenes containing objects that differ in colour, form multiple dichromatic planes in RGB space but the illuminant vector is common to all planes. The algorithm therefore counts the number of image pixels that intersect with a plane formed by the illuminant vector and its normal as the plane is rotated around the illuminant vector. In images comprising two objects that differ in colour, vegetation and soil for example, the method produces a bimodal histogram where the two modes correspond to clusters of pixels from the two objects. Data on plant reflectance spectra can be used to identify which of the clusters is vegetation. The performance of the method is assessed using receiver operator characteristic curves and the probability of misclassification is measured. (C) 2001 Elsevier Science B.V. All rights reserved.