An efficient method to improve the accuracy of Vietnamese vehicle license plate recognition in unconstrained environment

Abstract

Background: Most previous studies in automatic license plate recognition (ALPR) focused on recognizing license plate (LP) in constrained environment where cameras are installed in front of LPs and other conditions such as lighting, weather, and image quality are satisfied. Besides, recent studies on ALPR in Vietnam have conducted in small datasets and have not covered various cases of Vietnamese LPs.Aim: To develop a model for ALPR that is effective in unconstrained environment in Vietnam.Method: We propose two improvements: We apply the idea of the key-point detection problem for LP detection part, and use a segmentation free approach based on encoder decoder network for the LP optical character recognition (OCR) part. We train and evaluate models in a large dataset collected from unconstrained environment.Results: Our results show improvements in LP detection accuracy with mean IOU mIOU = 95.01% and precision P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">75</inf> = 99, 5%. The accuracy in LP OCR was up to Acc <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">seq</inf> = 99.28% at sequence level and Acc <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">char</inf> = 99.7% at character level.Conclusion: We provide a large dataset of Vietnamese LP images that can be effectively used to evaluate ALPR systems in Vietnam, and proposes improvement techniques to tackle problems of ALPR in unconstrained environment in Vietnam.