We have developed a method for measuring the shape of an object by integration of geometry-based and photometry-based methods for shape measurement. A major feature is that it does not need precise knowledge of surface reflectance of the object surface even though it uses photometric stereo.
The geometry-based method measures the object shape based on standard stereo. For example, a projector is used to project a series of structured patterns onto the object, and their projections are captuerd by a camera, from which the object shape is computed by triangulation. The photometry-based method measures the object shape based on photometric stereo; multiple images of the object are captured while changing illumination directions, from which the surface orientation of each poing on the object surface is computed. Their integration is performed as shown in the illustration below.
A highlight of our method is that it does not need a precise knowledge of reflectance property of the object surface nor a precise knowledge of illumination, which is usually necessary in standard photometric stereo. This is made possible by our theoretical anlyses as to what information can be derived from the images when no precise knowledge of surface reflectance/illumination is available.
Takayuki Okatani and Koichiro Deguchi, Optimal Integration of Photometric and Geometric Surface Measurements Using Inaccurate Reflectance/Illumination Knowledge, CVPR2012. [PDF]