Simple Shape-from-shading in the Dental and Medical Measurement Context

Stereo-photogrammetric intra-oral measurement of teeth has been reported previously to be worthwhile to dental research, but inherently difficult because of the lack of optical texture in the dental surfaces. Shape-from-shading (SFS) from single imagery suggests itself as an alternative technique for dental measurement simply because a lack of texture is a fundamental necessity for shape-from-shading measurement. Furthermore, because a number of areas of the human body, notably the back which is of interest in scoliosis studies, can lack strong texture, shape-from-shading is an attractive prospect for various other medical measurement tasks involving human body surfaces. Despite some immediate attractiveness, shape-from-shading has difficulties which may effectively preclude reliable measurement by single images in real medical situations, and the prospective medical user of SFS needs to be aware of certain challenges. Despite these problems, in certain cases where the object is defined by simple shapes, such as may be encountered in incisor teeth and other common external body areas, some three-dimensional results can be achieved. This paper examines some of the possibilities and pitfalls with dental and medical body measurement using simple shape-from-shading, and shows some result from imagery obtained on extracted teeth, on living teeth in the mouth and in other human measurement cases, in which the gaol is to obtain useful, precise, three-dimensional surface data.