We propose a method, based on finite-dimensional linear models of reflectance and illumination, which allows the transformation of chromatic images into color constant images. This proves to be useful in applications where either there is no information on the illuminant present in the scene, or when such information is confounded by the existence of inter-reflections between objects. This method is aimed at computations taking place beyond the sensory level of vision systems, and may use inputs corrected by sensors. In contrast to previous work, we show that good results can be obtained using a 3-receptor system and some knowledge about the spectral properties of natural materials and illuminants. In the method developed, an estimate of illuminant in the scene is computed, which allows the computation of color constant descriptors of the pixel values in the image. In addition, we show a method of computing the actual reflect ances of the materials in the scene out of the computed color descriptors.