Planar Shape Databases With Affine Invariant Search

Abstract

this paper we show how images in a database can be provided with additional information allowing viewpoint invariant shape query. Viewpoint invariance allows to compensate for affine or projective distortions, and is achieved by the usage of invariant reference frames. Those frames serve as a canonical coordinate system, common for all shapes in the database; in this system their similarity can be estimated and neighbourhood relationships can be established for subsequent search. The contributions of this work are twofold: first, the construction of such reference frames is done by combining different types of local invariant properties of the curve. Second, in the context of search operations, an important speed-up is introduced by means of momentbased indexing. Both strategies are tested on a database of trademarks. The database contains images of supermarket box packages with trademarks placed on their flat sides. Section 2 briefly describes the method for computing viewpoint-independent shape similarity. Section 3 presents the search mechanism, including indexing speed-up routine, and an evaluation of the results