2. Overview
Takes 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 area
is searched again from the image.
If characters are recognized then number plate search is terminated.
3. Steps Involved
Image division into small images
detecting probable number plate area
Recognizing number plate area
Parsing number plate to extract characters
Apply OCR to the parsed characters
6. Recognizing Plate
Search number plate in the broken pieces of vehicle image
Apply peak to valley to the candidate image pieces to further break the image piece
into possible character
Image piece with maximum peaks in candidate character is selected as the number
plate
Column signature of the number plate image Column signature of the another image piece
8. Recognition of Characters
Method of recognition of characters from an image containing these
characters is based on object recognition techniques used in Digital Image
Processing.
Two commonly used techniques
Template Matching using Correlation
Distance Measurement
9. Template Matching
Template 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
10. Correlation
Modified 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.
11. Result of Correlation
Basic 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.
12. Limitations
Noise 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 template
image is required