Global shape from shading for an endoscope image

Abstract

Okatani andD eguchi proposeda local Shape from Shading (SFS) methodf or endoscope images by assuming the point light, which is close to the projection center, to be at the projection center. We extended andmo difiedth eir methodan d deviseda global SFS algorithm for the reconstruction of the complex shape of an internal organ. Since the surface of an organ is not Lambertian in general, we obtained the bi-directional reflection distribution function (BRDF) curve by calibration using a robot arm to achieve accurate endoscope orientation and positioning. Inspiredb y the idea of Kimmel and Bruckstein, global SFS method is based on the identification of singular points on the distance map, which each has the surface normal pointing towards the light source. Equal distance contours are propagated from each singular point using a level set methodto get a local distance map of the surface. This is repeatedfor all singular points. After that, a set of local distance maps are selectedto be mergedto gether to construct a global distance map using a new scheme. The shape of the object can then be obtainedf rom the global distance map. Simulated and real experiments were performed to verify the algorithm. Experimental result of global SFS from a single real endoscope image of a human lung is quite good.