Automatic License Plate Recognition

Shyang Lih Chang*, Li Shien Chen, Yun Chung Chung, Sei Wan Chen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

621 Citations (Scopus)


Automatic license plate recognition (LPR) plays an important role in numerous applications and a number of techniques have been proposed. However, most of them worked under restricted conditions, such as fixed illumination, limited vehicle speed, designated routes, and stationary backgrounds. In this study, as few constraints as possible on the working environment are considered. The proposed LPR technique consists of two main modules: a license plate locating module and a license number identification module. The former characterized by fuzzy disciplines attempts to extract license plates from an input image, while the latter conceptualized in terms of neural subjects aims to identify the number present in a license plate. Experiments have been conducted for the respective modules. In the experiment on locating license plates, 1088 images taken from various scenes and under different conditions were employed. Of which, 23 images have been failed to locate the license plates present in the images; the license plate location rate of success is 97.9%. In the experiment on identifying license number, 1065 images, from which license plates have been successfully located, were used. Of which, 47 images have been failed to identify the numbers of the license plates located in the images; the identification rate of success is 95.6%. Combining the above two rates, the overall rate of success for our LPR algorithm is 93.7%.

Original languageEnglish
Pages (from-to)42-53
Number of pages12
JournalIEEE Transactions on Intelligent Transportation Systems
Issue number1
Publication statusPublished - 2004 Mar


  • Color edge detector
  • Fuzzification
  • License number identification
  • License plate locating
  • License plate recognition (LPR)
  • Self-organizing (SO) character recognition
  • Spring model
  • Topological sorting
  • Two-stage fuzzy aggregation

ASJC Scopus subject areas

  • Automotive Engineering
  • Mechanical Engineering
  • Computer Science Applications


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