Step 2. Discretized edge detectors. Assuming that is subdivided into pixels , , , the test functions , are specified through Display Formula
(2) and are supported on features and consisting of five or seven vertically adjacent pixels, respectively. Following the strategy described in eca, six different edge detectors , , , , , and (“quadratic measure filters") are defined as discretizations of the integrals Display Formula
(3)with , , and .