Duk Jun Park Rae-Hong Park Sang Uk Lee Jong-Soo Choi Hierarchical edge detection using the bidirectional information in edge pyramids. 65-75 1994 15 Pattern Recognition Letters 1 http://dx.doi.org/10.1016/0167-8655(94)90102-3 db/journals/prl/prl15.html#ParkPLC94