Edges Are Not Just Steps

Images contain step edges, line features and many feature types that are somewhere between the two. Traditional gradient based edge operators are tuned to detect step edges, and hence are unable to properly detect and localize other feature types. The Phase Congruency detector is used as a tool to identify the different feature types found in images. It is shown that there is a continuum of feature types between step edges and lines, and that most images have a broad distribution of all these feature types. It is concluded that in typical images gradient based operators detect and localize only a small fraction of features correctly.