Rotationally invariant texture based features

Content-based retrieval is ultimately dependent on the features used for the annotation of data and its efficiency is dependent on the invariance and robust properties of these features. For texture-based features an important form of invariance is rotational invariance. Novel rotationally invariant texture-based features are introduced that are extracted from a polar Fourier transform (PFT). The PFT is similar to the discrete Fourier transform in two dimensions but uses transform parameters radius and angle rather than the Cartesian co-ordinates. The PFT is discretised appropriately across the angular and radial frequency space with the transform magnitudes forming the rotationally invariant features. These features although rotationally invariant, capture the angular distribution together with the radial distribution of frequency within texture. Preliminary results show the method to give better results than rotationally variant and invariant Gabor filter schemes