Real-time radial symmetry for speed sign detection

Algorithms for classifying road signs have a high computational cost per pixel processed. A promising approach to real-time sign detection is to reduce the number of pixels to be classified as being a particular sign to a minimum by some form of sign detection on the image using less time expensive algorithms. In this paper, we adapt the fast radial symmetry detector to the image stream from a camera mounted in a car eliminate almost all non-sign pixels from the image stream. We then are able to apply normalised cross-correlation to classify the signs. This method is suitable for circular signs only; we apply it to Australian speed signs in this paper. Our results show that it is robust to a broad range of lighting conditions. Also, as the method is fast, there is no need to make unrealistically strict assumptions about image structure.