Practical methods for speeding-up the pairwise nearest neighbor method

Timo Kaukoranta University of Turku Turku Center for Computer Science Department of Computer Science Lemminkäisenkatu 14A FIN-20520 Turku, Finland Abstract. The pairwise nearest neighbor (PNN) method is a simple and well-known method for codebook generation in vector quantization. In its exact form, it provides a good-quality codebook but at the cost of high run time. A fast exact algorithm was recently introduced to implement the PNN an order of magnitude faster than the original O(N3K) time algorithm. The run time, however, is still lower bounded by O(N2K), and therefore, additional speed-ups may be required in applications where time is an important factor. We consider two practical methods to reduce the amount of work caused by the distance calculations. Through experiments, we show that the run time can be reduced to 10 to 15% that of the original method for data sets in color quantization and in spatial vector quantization. © 2001 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.1412423]