Improving pan-European speed-limit signs recognition with a new “global number segmentation” before digit recognition

In this paper, we present an improved European speed-limit sign recognition system based on an original ldquoglobal number segmentationrdquo (inside detected circles) before digit segmentation and recognition. The global speed-limit sign detection and correct recognition rate, currently evaluated on videos recorded on a mix of French and German roads, is around 94%, with a misclassification rate below 1%, and not a single validated false alarm in several hours of recorded videos. Our greyscale-based system is intrinsically insensitive to colour variability and quite robust to illumination variations, as shown by an on-road evaluation under bad weather conditions (cloudy and rainy) which yielded 84% good detection and recognition rate, and by a first night-time on-road evaluation with 75% correct detection rate. Due to recognition occurring at digit level, our system has the potential to be very easily extended to handle properly all variants of speed-limit signs from various European countries. Regarding computation load, videos with images of 640 times 480 pixels can be processed in real-time at ~20 frames/s on a standard 2.13 GHz dual-core laptop.