Multi-scale phase-based local features

Local feature methods suitable for image feature based object recognition and for the estimation of motion and structure are composed of two steps, namely the ´where´ and ´what´ steps. The ´where´ step (e.g., interest point detector) must select image points that are robustly localizable under common image deformations and whose neighborhoods are relatively informative. The ´what´ step (e.g., local feature extractor) then provides a representation of the image neighborhood that is semi-invariant to image deformations, but distinctive enough to provide model identification. We present a quantitative evaluation of both the ´where´ and the ´what´ steps for three recent local feature methods: a) phase-based local features (Carneiro and Jepson, 2002), b) differential invariants (Schmid and Mohr, 1997), and c) the scale invariant feature transform (SIFT) (Lowe, 1999). Moreover, in order to make the phase-based approach more comparable to the other two approaches, we also introduce a new form of multi-scale interest point detector to be used for its ´where´ step. The results show that the phase-based local features lead to better performance than the other two approaches when dealing with common illumination changes, 2D rotation, and sub-pixel translation. On the other hand, the phase-based local features are somewhat more sensitive to scale and large shear changes than the other two methods. Finally, we demonstrate the viability of the phase-based local feature in a simple object recognition system.