1. A method, comprising: chromatic classifying pixels of a digital image by, transforming a chromatic domain of definition of pixels from a three-dimensional space into a respective two-dimensional normalized space; defining a reference model of classification by analyzing a plurality of images of distinct types of subjects, generating distinct collections of samples with respective coordinates in the normalized two-dimensional space for each of a number of chromatic classes corresponding to real subjects; and classifying pixels by evaluating, based on the reference model and for each image pixel to be classified: a membership class; and a membership level within the membership class, wherein said reference model is defined by a parametric membership function continuous on said normalized two-dimensional space for each of said chromatic classes, parameters of which are determined by processing the collection of two-dimensional samples of each of said chromatic classes, said chromatic classifying, transforming, defining and evaluating being performed by one or more configured processing devices.