VEHICLE LICENSE PLATE DETECTION AND RECOGNITION
Table Of Contents
- TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................................................................................................... II LIST OF FIGURES ...................................................................................................................... V
ABSTRACT .................................................................................................................................... VII
Chapter ONE
INTRODUCTION
- AND BACKGROUND ................................................................... 1
- 1.1Research Topic and Objectives ................................................................................................. 1
- 1.2Challenges ......................................................................................................................... 2
- 1.3Background and Related Work ............................................................................................... 3 1.
- 3.1License Plate Detection ....................................................................................................... 4 1.
- 3.2Character Segmentation ....................................................................................................... 13 1.
- 3.3License Plate Recognition ..................................................................................................... 15
- 1.4Overview of Our Methods ...................................................................................................... 16 2 LICENSE PLATE DETECTION ................................................................................................ 18
- 2.1Scanning Window ............................................................................................................... 18
- 2.2HOG Features .................................................................................................................... 20 2.
- 2.1Feature Extraction Procedure (for Dense-HOG) .............................................................. 21 2.
- 2.2Implementation .............................................................................................................. 24
- 2.3Support Vector Machine ......................................................................................................... 24
- 2.4Non-maximum Suppression ..................................................................................................... 26
- 2.5Refinement of the Algorithm................................................................................................. 29
2.
- 5.1Edge Information.............................................................................................................. 29 2.
- 5.2Scale Adaption..................................................................................................................... 30
- 2.6Results and Discussion ........................................................................................................... 30
- 2.7Summary ............................................................................................................................. 31 3 LICENSE PLATE RECOGNITION ............................................................................................ 32
- 3.1License Plate Alignment Using Color Information................................................................... 34 3.
- 1.1License Plate Alignment Without Angles.............................................................................. 34 3.
- 1.2License Plate Alignment With Angles............................................................................ 38
- 3.2Plate Binarization Using K-means Clustering........................................................................... 40 3.
- 2.1K-means Clustering.............................................................................................................. 41
- 3.3Character Segmentation Using an Innovative Histogram-based Model ................................. 43
- 3.4Digit Characters and Capital Letters Recognition Using Simple Robust Features .................. 48 3.
- 4.1Using Bag-of-words Model: Voting Schemes........................................................................ 49 3.
- 4.2Using SVM Classifier.......................................................................................................... 53
- 3.5Data set and Results ............................................................................................................ 54
- 3.6Summary.................................................................................................................................... 57 4 REAL TIME EMBEDDED SYSTEM ............................................................................................ 58
- 4.1Hardware Part...................................................................................................................... 58
- 4.2Software Part.........................................................................................................................59 4.
- 2.1The Main Board Side............................................................................................................. 59 4.
- 2.2The Child Board Side........................................................................................................ 60
- 4.3Implementation..................................................................................................................... 62 4.
- 3.1Kernel Module................................................................................................................... 62 4.
- 3.2Main Board Program.......................................................................................................... 63 4.
- 3.3Socket and TCP................................................................................................................. 63 4.
- 3.4Child Board Program........................................................................................................ 64
- 4.4Results and Discussion.................................................................................................................................... 64 5 CONCLUSIONS AND FUTURE WORK ................................................................................. 66 REFERENCES .............................................................................................................................. 67
Thesis Abstract
Abstract
Vehicle license plate detection and recognition have gained significant attention in recent years due to their applications in various fields such as law enforcement, parking management, and traffic control. This research focuses on the development of an efficient system for accurately detecting and recognizing license plates from images or videos. The proposed system utilizes advanced image processing and deep learning techniques to first detect the presence of a license plate in an image or video frame. This initial step involves pre-processing the image to enhance the features of the license plate, followed by applying object detection algorithms to locate the plate within the image. Once the license plate is successfully detected, the system then employs optical character recognition (OCR) algorithms to extract the alphanumeric characters from the plate. This process involves segmenting the characters, enhancing their visibility, and utilizing machine learning models to recognize and interpret the characters accurately. The system is designed to be robust and efficient, capable of handling various challenges such as different lighting conditions, varying plate sizes and styles, and potential occlusions. To improve the accuracy and performance of the system, extensive training and testing of the deep learning models are conducted using large datasets of license plate images. The output of the system includes the recognized characters from the license plate, which can be further processed for various applications such as automated toll collection, parking access control, and vehicle tracking. The system's performance is evaluated based on metrics such as detection accuracy, recognition rate, and processing speed to ensure its effectiveness in real-world scenarios. Overall, the proposed system offers a comprehensive solution for vehicle license plate detection and recognition, leveraging the latest advancements in image processing and deep learning technologies. By accurately identifying license plates and extracting the relevant information, the system contributes to enhancing the efficiency and security of transportation systems and related services.
Thesis Overview
<p><b>1.0 INTRODUCTION AND BACKGROUND </b></p><p><b>1.1 Research Topic and Objectives </b></p><p>License Plate Recognition (LPR) is a problem aimed at identifying vehicles by detecting
and recognizing its license plate. It has been broadly used in real life applications such as traffic
monitoring systems which include unattended parking lots, automatic toll collection, and
criminal pursuit [5].
The target of this thesis is to implement a vehicle retrieval system for a Chinese
surveillance camera, by detecting and recognizing Chinese license plates. It will be useful for
vehicle registration and identification, and therefore may further contribute to the possibility of
vehicle tracking and vehicle activity analysis. </p><p>The proposed method includes two main steps: </p><p>1) License Plate Detection: Using SVM classifier with HOG features based on a sliding
window scheme, scan possible regions detected by edge information, and obtain license plate
candidates. Then apply Non-Maximum Suppression (NMS) to finalize the plate locations. </p><p>2) License Plate Recognition: The detected license plate will be aligned first, after which
its pixels can be successfully clustered by k-means into two classes: background pixels , and the
foreground pixels, e.g., the pixels of the characters. The plate is segmented afterwards, into
character patches that will be recognized using SVM classifier individually. </p><p><b>1.2 Challenges </b></p><p>The first challenge is plate variation. The plate can be various in location, quantity, size,
color, font, occlusion, inclination, and plates may contain frames or screws [1]. The second
challenge is environmental variation which includes change in illumination and background.
Weather conditions, lighting conditions, and even camera conditions may contribute to the
difficulty of this problem.
For Chinese license plates, the font is fixed except vanity plates designed by individuals,
which is very rare. Fig.1.1 shows some Chinese license plates from several provinces. The
challenge from the font is relieved while all the other challenges like variation in plate location,
plate quantity, its size, color, occlusion, and inclination still remains. The weather condition
where the images in the dataset are captured is various too. Images are captured in the daytime as
well as at night; the weather can be sunny or it can be rainy.
<br></p><p>
<b>1.3 Background and Related Work </b></p><p>License plate recognition (LPR) system contribute to applications such as traffic
surveillance, traffic law enforcement, automatic toll collection, vehicle parking identification,
and vehicle access control in a restricted area. Typically, an LPR system is composed of License
plate detection (LPD), license plate character segmentation (LPS) and License plate character
recognition (LPR).
License plate detection is commonly the first procedure in a LPR system. It aims at
locating the license plate, which provides the following LPR procedure with accurate region
information. Instead of processing every pixel in the input image of the system, which is very
time consuming, license plate detection is a necessary process before license plate recognition.
Methods on LPD can be classified into such categories based on the color level: 1) Binary
Image processing; 2) Gray-Level Processing; 3) Color Processing; 4) Classifiers [3]. While
based on the information used to detect the license plate, the LPD methods can be categorized
into six classes: 1) using edge information; 2) using global image information; 3) using texture
features; 4) using color features; 5) using character features; 6) combing two or more features [1].
<br></p><p>
1.<b>3.1 License Plate Detection </b></p><p><b>A. Using Edge or Boundary Information.</b></p><p><b> a. Filters </b></p><p>In [6]-[9], Sobel filter is used to detect edges, by which the boundaries of license plates
are represented due to color transition between the license plate and the car body. Two horizontal
lines are located when performing horizontal edge detection, and two vertical lines are located
when performing vertical edge detection. The rectangle is fixed when two set of lines are located
both at the same time. While in 2003, F. Kahraman [2] et al. applied Gabor filters to detect
license plate regions which achieved a good performance when images are of a fixed angle.
Gabor filters are helpful in analyzing textures as they are sensitive to textures with different
scales and directions.
b. Edge Detection
Based on the intuitive that the license plate is of some shape, most likely rectangular,
whose aspect ratio is known, methods are commonly used to extract plates from all possible
rectangles. Edge Detection methods are such ones to find the rectangles [10]-[13]. Edges can be
detected only vertically or horizontally, and can be statistically analyzed to determine license
plate candidate regions [12]. A fast vertical edge detection algorithm (VEDA) was proposed in
[14] for license plate detection, which is declared to be faster than Sobel operator by around
seven to nine times
<br></p>