Recognition and retrieval of textured images using gradient indexing

We investigate the use of gradient indexing for texture discrimination. From a histogram of its gradient field, a texture can be recognized. We find that gradient indexing is insensitive to the number of bins and to the choice of the gradient operator. We also find that the gradient direction and magnitude are both important in recognizing different textures. We further propose a modified gradient indexing technique called local activity spectrum, which has improved performance