An invariant scheme for exact match retrieval of symbolic images based upon principal component analysis

In this paper, an important aspect in creating a symbolic image database (SID), useful for exact match retrieval is addressed. The problem in conventional pairwise spatial relationships (particularly the 9DLT matrix) based approach for representing symbolic images in SID is discussed. An efficient method specifically for exact match retrieval, invariant to image transformations is proposed. In order to take care of image transformations, a new concept called direction of reference is introduced. The relative spatial relationships existing among the components present in an image are perceived with respect to the direction of reference and preserved by a set of triples. The proposed method is based upon principal component analysis (PCA). The first principal component vector (PCV) of the set of triples corresponding to an image is computed and stored as the representative of that image. The PCVs corresponding to n images to be archived in the SID are stored in a sorted order. A methodology for exact match retrieval is also presented in this paper. The presented retrieval algorithm takes O(log n) search time in the worst case, with the help of the binary search technique, where n is the number of symbolic images stored in the SID.