A Bucket Grid Structure to Speed Up Table Lookup in Gauge-Based Photometric Stereo

In this paper, we show how to speed up the table lookup step in gauge-based multi-image photometric stereo. In that step, one must find a pixel of a gauge object, of known shape and color, whose appearance under m different illumination fields is similar to that of a given scene pixel. This search reduces to finding the closest match to a given m- vector in a table with a thousand or more m-vectors. Our speed-up method exploits the fact that the table is in fact a fairly flat two-dimensional manifold in m-dimensional space, so that the search can be efficiently solved with a two-dimensional bucket grid structure.