Correction and Extraction of Perspectively Distorted License Plates Using Scan Line Based Generalized Symmetry Transform

Dong-Su KIM; Il CHOI; Sung-Il CHIEN

Correction and Extraction of Perspectively Distorted License Plates Using Scan Line Based Generalized Symmetry Transform

Dong-Su KIM, Il CHOI, Sung-Il CHIEN

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This paper presents a method of extracting car license plates captured from the arbitrary directions by using symmetry features. The generalized symmetry transform (GST) produces continuous features of symmetry between two points by combining locality constraint and reflectional symmetry, but its time complexity of GST is increased by the second power of the radius of a searching window. To achieve considerable reduction of this time complexity, we propose a scan line based GST (SLGST) which calculates the symmetry between a pair of edge pixels along the scan lines. Instead of calculating the global symmetry of a license plate, we assign the symmetry contribution acquired from SLGST to the corner point estimated from two edge points and their gradient orientations. The right angle tuned SLGST (RATSLGST) is newly proposed to detect the right angle corners more effectively. Image normalization by image warping is adopted to make such segmentation of license plate and later identification much easier. We also adopt the verifier that evaluates a candidate license plate to enhance extraction rate. Our experiments show that the proposed method for extracting perspectively distorted license plates is fairly reliable.

Publication: IEICE TRANSACTIONS on Information Vol.E85-D No.11 pp.1776-1783

Publication Date: 2002/11/01

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Type of Manuscript: Special Section PAPER (Special Issue on Information System Technologies for ITS)

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Dong-Su KIM, Il CHOI, Sung-Il CHIEN, "Correction and Extraction of Perspectively Distorted License Plates Using Scan Line Based Generalized Symmetry Transform" in IEICE TRANSACTIONS on Information, vol. E85-D, no. 11, pp. 1776-1783, November 2002, doi: .
Abstract: This paper presents a method of extracting car license plates captured from the arbitrary directions by using symmetry features. The generalized symmetry transform (GST) produces continuous features of symmetry between two points by combining locality constraint and reflectional symmetry, but its time complexity of GST is increased by the second power of the radius of a searching window. To achieve considerable reduction of this time complexity, we propose a scan line based GST (SLGST) which calculates the symmetry between a pair of edge pixels along the scan lines. Instead of calculating the global symmetry of a license plate, we assign the symmetry contribution acquired from SLGST to the corner point estimated from two edge points and their gradient orientations. The right angle tuned SLGST (RATSLGST) is newly proposed to detect the right angle corners more effectively. Image normalization by image warping is adopted to make such segmentation of license plate and later identification much easier. We also adopt the verifier that evaluates a candidate license plate to enhance extraction rate. Our experiments show that the proposed method for extracting perspectively distorted license plates is fairly reliable.
URL: https://global.ieice.org/en_transactions/information/10.1587/e85-d_11_1776/_p

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@ARTICLE{e85-d_11_1776,
author={Dong-Su KIM, Il CHOI, Sung-Il CHIEN, },
journal={IEICE TRANSACTIONS on Information},
title={Correction and Extraction of Perspectively Distorted License Plates Using Scan Line Based Generalized Symmetry Transform},
year={2002},
volume={E85-D},
number={11},
pages={1776-1783},
abstract={This paper presents a method of extracting car license plates captured from the arbitrary directions by using symmetry features. The generalized symmetry transform (GST) produces continuous features of symmetry between two points by combining locality constraint and reflectional symmetry, but its time complexity of GST is increased by the second power of the radius of a searching window. To achieve considerable reduction of this time complexity, we propose a scan line based GST (SLGST) which calculates the symmetry between a pair of edge pixels along the scan lines. Instead of calculating the global symmetry of a license plate, we assign the symmetry contribution acquired from SLGST to the corner point estimated from two edge points and their gradient orientations. The right angle tuned SLGST (RATSLGST) is newly proposed to detect the right angle corners more effectively. Image normalization by image warping is adopted to make such segmentation of license plate and later identification much easier. We also adopt the verifier that evaluates a candidate license plate to enhance extraction rate. Our experiments show that the proposed method for extracting perspectively distorted license plates is fairly reliable.},
keywords={},
doi={},
ISSN={},
month={November},}

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TY - JOUR
TI - Correction and Extraction of Perspectively Distorted License Plates Using Scan Line Based Generalized Symmetry Transform
T2 - IEICE TRANSACTIONS on Information
SP - 1776
EP - 1783
AU - Dong-Su KIM
AU - Il CHOI
AU - Sung-Il CHIEN
PY - 2002
DO -
JO - IEICE TRANSACTIONS on Information
SN -
VL - E85-D
IS - 11
JA - IEICE TRANSACTIONS on Information
Y1 - November 2002
AB - This paper presents a method of extracting car license plates captured from the arbitrary directions by using symmetry features. The generalized symmetry transform (GST) produces continuous features of symmetry between two points by combining locality constraint and reflectional symmetry, but its time complexity of GST is increased by the second power of the radius of a searching window. To achieve considerable reduction of this time complexity, we propose a scan line based GST (SLGST) which calculates the symmetry between a pair of edge pixels along the scan lines. Instead of calculating the global symmetry of a license plate, we assign the symmetry contribution acquired from SLGST to the corner point estimated from two edge points and their gradient orientations. The right angle tuned SLGST (RATSLGST) is newly proposed to detect the right angle corners more effectively. Image normalization by image warping is adopted to make such segmentation of license plate and later identification much easier. We also adopt the verifier that evaluates a candidate license plate to enhance extraction rate. Our experiments show that the proposed method for extracting perspectively distorted license plates is fairly reliable.
ER -