In this paper we propose an image retrieval scheme based on projectively invariant features. Since cross-ratio is the fundamental invariant feature under projective transformations for points, we use that as the basic feature parameter. We compute the cross-ratios of point sets in quadruplets and a discrete representation of the distribution of the cross-ratio is obtained from the computed values. The distribution is used as the feature for retrieval purposes. The method is very effective in retrieving images having similar planar 3D structures like buildings.
S. Rajashekhar, Subhasis Chaudhuri, Vinay P. Nambo