Shading and Lighting Normalization

Now that pose variation has been considered, we turn our attention to the next most prominent source of variance in facial appearance that we wish to eliminate: lighting. Lighting can cause radical changes in the intensities of an image by varying from severe darkness to extreme brightness. Furthermore, lighting might be directional and cause one side of the face to be brighter than the other. Varying and nonuniform lighting need to be compensated for so that the large amount of variance they account for can be removed for recognition. Illumination corrections will be applied via histogram fitting.