Lossless Location Coding for Image Feature Points

Image retrieval research activity has moved its focus from global descriptors to local descriptors of feature point such as SIFT. Currently MPEG is working on standardization of effective coding of location and local descriptors of feature point in the context mobile based image search driven application in the name of MPEG-7 CDVS (Compact Descriptor for Visual Search). While CDVS is dealing with lossy compression of location information, this paper presents various lossless compression methods of locations and provides comparative experimental results for applications requiring fine matching precision. Among 4 methods presented in this paper, Experimental results show that Block-based lossless location coding using circular scan order method shows the best compression results with compression ratio achieving 2.5 to 1 with reference to Fixed-Length lossless location coding method.