Polygonal symmetry transform for detecting rectangular traffic signs

We present a new symmetry transform finding rectangles based on a gradient and corner information of images. We succeed the Fast Radial Symmetry Transform (FRST) finding radial objects with low cost and high accuracy. But FRST focused on using image gradient to find small circle shapes so that FRST can not detect larger polygonal shapes well. Our transform used image gradient and image corner to construct polygonal symmetry maps and extract regions of interest from images. We referred the set of polygon features as the Polygonal Symmetry Transform (PST). Then PST has large coverage with the advantages of FRST. To verify PST, we designed a polygon detectors which finds the road traffic sign such as radial and polygonal shapes. Our detector extracted regions of interest from real road images and calculated performances including detection rate for traffic signs and processing time per image in our experiments.