Characterization of keypoints in images.

In this contribution we investigate the performance of steerable functions to characterize keypoints. Steerable functions were introduced recently by Perona as an efficient method to calculate the response of a filter in a continuum of orientations, scales, and other parameters. For the analysis of points with events at multiple orientations, functions with a high orientational resolution are needed. We discuss criteria to judge the quality of a function to serve for orientation analysis. To handle line as well as edge junctions, we use a complex function with the real and imaginary part approximately in quadrature. An associated one-sided function allows to distinguish between terminating and nonterminating edges and lines. To analyze thick lines and blurred edges the function is also steered in scale