On the Rayleigh nature of Gabor filter outputs

Texture has been recognized as an important visual primitive in image analysis. A widely used texture descriptor, which is part of the MPEG-7 standard, is that computed using multiscale Gabor filters. The high dimensionality and computational complexity of this descriptor adversely affect the efficiency of content-based retrieval systems. We propose a modified texture descriptor that has comparable performance, but with nearly half the dimensionality and less computational expense. This gain is based on a claim that the distribution of (absolute values of) filter outputs have a strong tendency to be Rayleigh. Experimental results show that the dimensionality can be reduced by almost 50%, with a tradeoff of less than 3% on the error rate. Furthermore, it is easy to compute the new feature using the old one, without having to repeat the computationally expensive filtering step. We also propose a new normalization method that improves similarity retrieval and indexing efficiency.