Optical Character Recognitionon Vehicle Number PlateAvinash Singh Bagri2009MT50541EEL 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 areaRecognizing number plate areaParsing number plate to extract charactersApply OCR to the parsed characters
Extracting Number PlateOne piece of image that will be tested for number plate
Recognizing PlateSearch number plate in the broken pieces of vehicle imageApply peak to valley to the candidate image pieces to further break the image pieceinto possible characterImage piece with maximum peaks in candidate character is selected as the numberplateColumn signature of the number plate image Column signature of the another image piece
Recognition of CharactersMethod of recognition of characters from an image containing thesecharacters is based on object recognition techniques used in Digital ImageProcessing.Two commonly used techniquesTemplate Matching using CorrelationDistance Measurement
Template MatchingTemplate matching using correlationBased on performing correlation between segmented imageA character is required to be recognized and character template imagewhich is used for recognition
CorrelationModified form of convolutionf(x,y): gray scale value at a specific element (x,y) in an imagef(x,y): imageg(x,y) character templateh(x,y) image after correlation.
Result of CorrelationBasic form of convolutionResult is an image, convolution of two matricesThe size of result matrix will be increased from input image matricesDue to which we have to apply some thresh holding on resultant imageNormally value of thresh hold is little less than maximum value of resultantimage.
LimitationsNoise free image with uniform illumination requiredNumbers must be displayed in one line on the number plateProblem associated with template image is proper acquisition of templateimage is required
Referenceshttp://www.sersc.org/journals/IJUNESST/vol6 no1/2.pdfhttp://www.ele.uri.edu/~hansenj/projects/ele585/OCR/OCR.pdfhttp://perun.pmf.uns.ac.rs/radovanovic/dmsem/completed/2006/OCR.pdfhttp://www.nicomsoft.com/optical-character-recognition-ocr-how-it-works/http://www.ancient-asia-journal.com/article/view/aa.06113/25License 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