Morphological methods for detection and classification of edges in range images

Range images provide an explicit encoding of the shape and geometric structure of the objects in the image from the point of view of the sensor. Since morphological methods are inherently geometric in nature, they are ideally suited for the analysis of range images. However, morphological edge operators meant for intensity images cannot be used to detect edges in range images because roof and crease edges do not correspond to depth discontinuity. In this paper two schemes for detection and classification of edges in range images based on morphological operations are presented. The first method uses the residues of openings and closings to detect roof and crease edges. Directional sensitivity to edges is incorporated by using structuring elements oriented in different directions. The second method employs the residues of dilation and erosion at multiple scales and provides a richer description of the surface structure at each point in the image by classifying each pixel as belonging to one of the eight possible structure types: positive roof, negative roof, positive crease, negative crease, top of step, base of step, ramp, and constant surface. Several examples, including some involving the fusion of edge information from registered range/intensity images, are presented.