Optical Character Recognition on Vehicle Number Plate

Avinash Singh Bagri

2009MT50541

EEL 709Dr Sumeet Agarwal

OverviewTakes image of the car and searches for the number plate in the image.

Once the probable number plate area is located it is given to OCR.

If OCR doesn’t recognize the characters from the image number plate areais searched again from the image.

If characters are recognized then number plate search is terminated.

Steps InvolvedImage division into small imagesdetecting probable number plate area

Recognizing number plate area

Parsing number plate to extract characters

Apply OCR to the parsed characters

Example

Original Image

Binarised image

Inverted binarised image

Extracting Number Plate

One piece of image that will be tested for number plate

Recognizing PlateSearch number plate in the broken pieces of vehicle image

Apply peak to valley to the candidate image pieces to further break the image pieceinto possible character

Image piece with maximum peaks in candidate character is selected as the numberplate

Column signature of the number plate image Column signature of the another image piece

Parsing plate

Images of all characters

Recognition of CharactersMethod of recognition of characters from an image containing these characters is based on object recognition techniques used in Digital Image Processing.

Two commonly used techniquesTemplate Matching using Correlation

Distance Measurement

Template MatchingTemplate matching using correlation

Based on performing correlation between segmented image

A character is required to be recognized and character template image which is used for recognition

CorrelationModified form of convolution

f(x,y): gray scale value at a specific element (x,y) in an image

f(x,y): image

g(x,y) character template

h(x,y) image after correlation.

Result of CorrelationBasic form of convolution

Result is an image, convolution of two matrices

The size of result matrix will be increased from input image matrices

Due to which we have to apply some thresh holding on resultant image

Normally value of thresh hold is little less than maximum value of resultant image.

LimitationsNoise free image with uniform illumination required

Numbers must be displayed in one line on the number plate

Problem associated with template image is proper acquisition of templateimage is required

Referenceshttp://www.sersc.org/journals/IJUNESST/vol6 no1/2.pdf

http://www.ele.uri.edu/~hansenj/projects/ele585/OCR/OCR.pdf

http://perun.pmf.uns.ac.rs/radovanovic/dmsem/completed/2006/OCR.pdf

http://www.nicomsoft.com/optical-character-recognition-ocr-how-it-works/

http://www.ancient-asia-journal.com/article/view/aa.06113/25

License Plate Number Recognition - New Heuristics and a Comparative Study of Classifiers (2F79e4150656ca79aeb9.pdf)

Kwaśnicka H. and WawrzyniakLicense B.; Plate Localization and Recognition in Camera Pictures

Thank you