Automatic Number Plate Recognition (ALPR)

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Abstract

Automatic number plate recognition (ANPR) is the method of extraction of vehicle number plate information from an image or a sequence of images. The extracted data can be used in many applications, such as toll booths and vehicle parking areas where payment can be done electronically and traffic surveillance systems. The images are taken by the ANPR systems using either a color , black and white or an infrared camera, depending on which different techniques are applied for extraction of information. The quality of image plays a vital role in the successful extraction of license data. For ANPR to be a real life application it has to quickly and successfully process license plates under different environmental conditions, such as day …show more content…

The license plates can be partially occluded by dirt,
lighting, and towing accessories on the car. In this paper, we
present a comprehensive review of the state-of-the-art techniques
for ALPR. We categorize different ALPR techniques according
to the features they used for each stage, and compare them in
terms of pros, cons, recognition accuracy, and processing speed.
Future forecasts of ALPR are given at the end.

I. Introduction
AUTOMATIC license plate recognition (ALPR) plays an important role in numerous real-life applications, such
as automatic toll collection, traffic law enforcement, parking lot access control, and road traffic monitoring [1]–[4].
ALPR recognizes a vehicle’s license plate number from an
image or images taken by either a color, black and white,
or infrared camera. It is fulfilled by the combination of a
lot of techniques, such as object detection, image processing,
and pattern recognition. ALPR is also known as automatic
vehicle identification, car plate recognition, automatic number
plate recognition, and optical character recognition (OCR) for
cars. The variations of the plate types or environments cause
challenges in the detection and recognition of license plates.
They are summarized as follows.
1) Plate …show more content…

Two characters are grouped together if the gap between the bounding boxes found along the x and y coordinate are less than (p1* h) and (p2*h) where h is height of the bounding box and p1 , p2 are system parameters. Here it is noteworthy that these gaps are the actual gaps present between the two individual characters in the number plates along x axis and y axis accordingly. The gap between the characters along x axis varies in a finite range while the gaps along the y axis are fixed for a dual line license plate as is seen in the image below. But for the case of tilted license plates the gap along y axis also changes in accordance to the the angle of

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