Angle vertex and bisector geometric model for triangular road sign detection

We present a new transformation for angle vertex and bisector detection. The vertex and bisector transformation (VBT) takes the image gradient as input and outputs two arrays, accumulating evidence of respectively angle vertex and angle bisector. A geometric model of the gradient orientation is implemented using a pair-wise voting scheme: normal vectors of two adjacent sides of a triangle have a specific relationship depending on the corresponding vertex angle. Our approach is able to accurately detect vertices and bisectors of a triangular road sign in a 360 × 270 image in about 50 ms with no particular optimization. We tested our approach on a 48 images database containing 40 triangular signs with different colors and orientations (red intersection and give way warnings, blue pedestrian crossing): 33 are correctly detected (82%) and 7 are missed with 2 false positives.