Published on Dec 12, 2015
Automatic Number Plate Recognition or ANPR is a technology that uses pattern recognition to 'read' vehicle number plates.
" work by tracking vehicles' travel time between two fixed points, and therefore calculate the average speed
"In simple terms ANPR cameras 'photograph' the number plates of the vehicles that pass them. This 'photograph' is then fed in a computer system to find out details about the driver and owner of the vehicle and details about the vehicle itself
"ANPR consists of cameras linked to a computer.
"As a vehicle passes, ANPR 'reads' Vehicle Registration Marks - more commonly known as number plates - from digital images, captured through cameras located either in a mobile unit, in-built in traffic vehicles or via Closed Circuit Television (CCTV).
"The digital image is converted into data, which is processed through the ANPR system.
ANPR is used for Detecting crime through the use of intelligence monitoring.
o Identifying stolen vehicles.
o Detecting vehicle document crime
o electronic toll collection etc.
There are six primary algorithms that the software requires for identifying a licence plate:
1.Plate localisation - responsible for finding and isolating the plate on the picture
2.Plate orientation and sizing - compensates for the skew of the plate and adjusts the dimensions to the required size
3.Normalisation - adjusts the brightness and contrast of the image
4.Character segmentation - finds the individual characters on the plates
5.Optical character recognition
6.Syntactical/Geometrical analysis - check characters and positions against country specific rules
oPoor image resolution, usually because the plate is too far away but sometimes resulting from the use of a low-quality camera.
oBlurry images, particularly motion blur and most likely on mobile units
oPoor lighting and low contrast due to overexposure, reflection or shadows
oAn object obscuring the plate, quite often a tow bar, or dirt on the plate
oA different font, popular for vanity plates