Ph.D. Theses

1998

This work addresses several issues in the field of computer vision. In particular, attention is focussed on the problem of the representation of an object from its appearance in an image. Several advances are proposed for the representation of planar shapes, which are thus suitable for representing planar and faceted objects. The representation developed is employed for content-based retrieval from an image database. The proposed projectively invariant description for groups of planar disjoint contours as a simultaneous polar reparametrization of multiple curves. Its origin is an invariant point and, for each ray orientation, the cross-ratio of the intersections with the closest curves gives the radius. The sequence of cross-ratio values for all orientations forms a signature. With respect to other methods, this representation is less reliant on individual curve properties, both for the construction of the reference frame and for the calculation of the signature. At the same time, this representation is local and integrates information from multiple curves, guaranteeing robustness to curve discontinuities and partial occlusions. Chromatic information is introduced into the representation and offers two advantages. First, the representation provides a more complete description of the shape and thus becomes more discriminative. Secondly, the chromatic description is illumination invariant under a diagonal chromaticity model and one more acquisition variable is therefore removed. The proposed representation was originally developed for planar shapes, but an extension has been proposed and validated for trihedral corners. [truncated]