Methods for Indexing Stripes in Uncoded Structured Light Scanning Systems

This paper presents robust methods for determining the order of a sequence of stripes captured in an uncoded structured light scanning system, i.e. where all the stripes are projected with uniform colour, width and spacing. A single bitmap image shows a pattern of vertical stripes from a projected source, which are deformed by the surface of the target object. If a correspondence can be determined between the projected stripes and those captured in the bitmap, a spatial measurement of the surface can be derived using standard rangefinding methods. Previous work has uniquely encoded each stripe, such as by colour or width, in order to avoid ambiguous stripe identification. However, colour coding suffers due to uneven colour reflection, and a variable width code reduces the measured resolution. To avoid these problems, we simplify the projection as a uniform stripe pattern, and devise novel methods for correctly indexing the stripes, including a new common inclination constraint and occlusion classification. We give definitions of patches and the continuity of stripes, and measure the success of these methods. Thus we eliminate the need for coding, and reduce the accuracy required of the projected pattern; and, by dealing with stripe continuity and occlusions in a new manner, provide general methods which have relevance to many structured light problems.