Invariant-Based Shape Retrieval in Pictorial Databases

One of the strongest cues for retrieval of content information from images is shape. However, due to the wide range of transformations that an object might undergo, this is also the most difficult one to handle. It seems that shape retrieval is one of the major barriers nowadays to image databases being commonly used. We present an approach for shape retrieval from pictorial databases which is based on invariant features of the image. In particular we use a combination of semi-local multivalued invariant signatures and global features. Spatial relations and global properties are used to eliminate nonrelevant images before similarity is computed. The advantages of the proposed approach are its ability to handle images distorted by different viewpoint transformations, its ability to retrieve images even in situations in which part of the shape is missing (i.e., in case of occlusion or sketch-based queries), and its ability to support efficient indexing. We have implemented our approach in a heterogeneous database having a SQL-like user interface augmented with sketch-based queries. The system is built on top of a commercial database system and can be activated from the Web. We present experimental results demonstrating the effectiveness of the proposed approach.