  We show that for a plane imaged by an endoscope the specular isophotes are
concentric circles on the scene plane, which appear as nested ellipses in the
image. We show that these ellipses can be detected and used to estimate the
plane's normal direction, forming a normal reconstruction method, which we
validate on simulated data. In practice, the anatomical surfaces visible in
endoscopic images are locally planar. We use our method to show that the
surface normal can thus be reconstructed for each of the numerous specularities
typically visible on moist tissues. We show results on laparoscopic and
colonoscopic images.
