Number Plate Recognition
Azhar Sabah Abdulaziz
Summary
Number Plate Recognition (NPR) systems are used to extract the licence number of
vehicles from an image or video stream. In both cases, pattern recognition is applied
to locate the number plate, and character recognitions used for reading the licence
number. Different NPR systems have been implemented with varying levels of
occupancy and complexity.
Plate extraction is the most important and complicated step in the NPR system. The
aim of this project is to design a system that has an acceptance rate of successful plate
recognition and a low complexity. Many studies have been conducted that suggest
using a combination of both edge detection and image morphological analysis; in
order to reduce the computational expense. Edge Map Statistics (EMS) is a novel
method that was proposed first in this thesis; it was simulated and had a short
computational time compared to other methods. However, it could not be adopted
because it had an inadequate accuracy and did not respond very well to images o0f
different illustration. EMS might be considered to be an approximation of the Hough
transform and it was applied on the edge map after connected component analysis.
The adopted algorithm for plate extraction was the Multiple Morphological Filtration
(MMF) method; which has a slightly larger computational expense than the EMS, but
it is more accurate,. It is based on a set of morphological operations that are applied
to the edge map. In MMF, the irrelevant objects are detected by their lo9cation and
connectivity information; leaving the plate region as the highest contrast object from
the remaining components. The final step of the NPR system is the optical Character
Recognition (OCR) which is preceded by pre-processing operations applied on the
extracted plate in order to improve discriminating characters from the number plate
background. While the characters were segmented using connected component
analysis, Hamming distance was used for matching those characters with the database
as a final recognition step
Experiments have shown the advantages of combining connected component analysis
with the morphological operations in pattern recognition problems. This combination
simplifies the classification methodology and reduces the overall complexity greatly.