Compact and Accurate Early Vision Processing in the Harmonic Space

The efficacy of anisotropic versus isotropic filtering is analyzed with respect to general phase-based metrics for early vision attributes. We verified that the spectral information content gathered through oriented frequency channels is characterized by high compactness and flexibility, since a wide range of visual attributes emerge from different hierarchical combinations of the same channels. We observed that it is preferable to construct a multichannel, multiorientation representation, rather than using a more compact representation based on an isotropic generalization of the analytic signal. The complete harmonic content is then combined in the phase-orientation space at the final stage, only, to come up with the ultimate perceptual decisions, thus avoiding an "early condensation" of basic features. The resulting algorithmic solutions reach high performance in real-world situations at an affordable computational cost.