Vehicle number plate recognition systems are expected to have numerous applications in traffic surveying and monitoring, e.g. finding stolen cars, controlling access to car parks and gathering traffic flow statistics. The Computer Vision Group at the University of Trás-os-Montes e Alto Douro, in collaboration with the Universities of Aveiro and Bristol, has been developing a number plate reading system. The system builds on the experience gained by the Computer Vision Group at the University of Bristol while developing previous transputer based prototypes.

The main tasks of a number plate recognition system are the location of the number plate area in the image, the segmentation of the characters and their identification. These tasks are strongly inter-related, mainly because the way to check if the number plate has been correctly located is based on the result of the character identification process (the result should correspond to a predefined syntax).

For the location of the number plate area in the image, a new line-based method has been developed. The method, instead of looking for character like shapes in the image, takes advantage of the “signature” of the number plate area in a horizontal cross-section of the image. An OCR (Optical Character Recognition) engine has been built, based on the critical points method first proposed by Shchepin & Nepomnyashchii. The syntax checking module is at the moment of a simple nature. It is mainly used to distinguish letters from numbers, in difficult cases (e.g. “B,8” and “O,D”).

The team

J Barroso, L Barbosa, J Bulas Cruz, A Rafael, E L Dagless

This project has also the collaboration of final year students of the Degree in Electrical Engineering in the University of Trás-os-Montes e Alto Douro (UTAD).

References

Barroso J, Bulas-Cruz J, Rafael J & Dagless E L, Identificação Automática de Placas de Matrícula Automóveis, 5.as Jornadas Luso-Espanholas de Engenharia Electrotécnica, 1997, Salamanca, Espanha, Julho (1997).

J. Barroso, A. Rafael, E. L. Dagless and J. Bulas-Cruz, Number plate reading using computer vision, IEEE - International Symposium on Industrial Electronics ISIE’97, Universidade do Minho, Guimarães, Portugal, Julho (1997).

Barroso J, Bulas-Cruz J & Dagless E L, Real-Time Number Plate Reading, 4th IFAC Workshop on Algorithms and Architectures for Real-time Control, Vilamoura, Portugal, Abril (1997).

Barroso J, Identificação Automática de Placas de Matrícula Automóveis, MsC Thesis in Electronic and Telecomunications Engineering, Universidade de Aveiro, Portugal, Dezembro (1995).

Barroso J, Bulas-Cruz J, Rafael J & Dagless E L, Identificação Automática de Placas de Matrícula Automóveis, 4.as Jornadas Luso-Espanholas de Engenharia Electrotécnica, Porto, Portugal, Julho (1995), ISBN 972-752-004-9.

Bulas-Cruz J, Image Processing Applications using a Transputer-based System, PhD Thesis, Universidade de Bristol, UK, Julho (1995).

Other Number Plate Recognition Systems