The treatment and diagnostic method known in medicine as PhotoDerm is actually based in a concept in physics known as photometric stereo, which gives the ability to estimate local surface orientation by using several images of the same surface taken from the same viewpoint but under illumination from different directions. Woodham first introduced it. The light sources are ideally point sources some distance away in different directions, so that in each case there is a well-defined light source direction from which to measure surface orientation. Therefore, the change of the intensities in the images depends on both local surface orientation and illumination direction.
Photometric stereo is a way in which the ill-posed problems in shading from shading can be resolved. It uses several images of the same surface under different illumination directions. The advantages of photometric stereo are:
1) Unlike single image shape from shading algorithms, photometric stereo makes no assumption of the smoothness of the surface, which it makes it quite useful in determining surfaces so individual as the skin.
The system triggers up to 16 lights, one at a time, synchronized with a high-speed video camera to capture views of a surface under various lighting directions. Photometric stereo is used to extract surface normals, and reflectance transformations to relight objects by introducing specular highlights.
In the past, ...