Image clustering for estimation of illumination spectra

This disclosure concerns processing of electronic images, such as hyperspectral or multispectral images. A processor performs a method for estimating an illumination spectrum of an image which defines an input spectrum for each point of the image. The processor determines for each point of a first set of points a measure of variation in relation to the input spectrum of that point. The processor then selects one point from the first set based on the measure of variation. The processor determines a cluster of points based on the input spectrum of the selected point and determines an estimate for the illumination spectrum based on the input spectra of points in the cluster. Since the processor selects a point based on the measure of variation and then determines a cluster based on that point, it performs better than using other methods where the cluster is determined based on a random starting point, for example.