Systematic Phase-based interpretation of early vision processing
by
Giulia Gastaldi
Department of Biophysical and Electronic Engineering (DIBE) at the University of Genoa, Italy
Coauthors: Sabatini, S. P., Solari, F., Chessa, M.

The goal of early vision is to extract as much information as possible about the structural properties of the visual signal without resorting to any a priori knowledge.

Considering the space/spatial-frequency duality the receptive fields of the primary visual cortex cells can be represented as a set of independent channels selectively sensitive to different limited ranges of spatial frequencies. Therefore, it is formally possible to derive a complete harmonic representation (phase, energy, and orientation) of any visual stimulus, by defining the associated analytic signal in a combined space-frequency domain through filtering operations with complex-valued band-pass kernels with different orientations.

In the last two decades the popularity of phase information, as a robust feature descriptor, has risen by relating perceptual features on measures of the local phase properties of the visual signal. Yet, the problem of interaction among oriented frequency channels has never been systemathically analyzed. On the basis of the fact that the extraction of local phase information in two dimensions is intrinsically an anisotropic problem, we consider local image orientation as an integral part of the harmonic representation. We verified that interactions across orientation channels must be considered to properly obtain reliable visual features.

Date received: March 13, 2008