What are good algorithms for vehicle license plate detection? [closed]

Answer 1

Here's how I suggest you should do this task. Read my detailed answer here.

1. Convert to Grayscale.
2. Gaussian Blur with 3x3 or 5x5 filter.

3. Apply Sobel Filter to find vertical edges.

   Sobel(gray, dst, -1, 1, 0)

4. Threshold the resultant image to get a binary image.
5. Apply a morphological close operation using suitable structuring element.
6. Find contours of the resulting image.
7. Find minAreaRect of each contour. Select rectangles based on aspect ratio and minimum and maximum area.
8. For each selected contour, find edge density. Set a threshold for edge density and choose the rectangles breaching that threshold as possible plate regions.
9. Few rectangles will remain after this. You can filter them based on orientation or any criteria you deem suitable.
10. Clip these detected rectangular portions from an image after adaptiveThreshold of the original (grayscale) image and apply OCR.

Answer 2

UK already has a system that does that. I recall seeing a TV show in which they demonstrated they can find a car within London within 10 minutes (assuming they know the number and the car is driving around) Just reading Wikipedia gives you the pointers you need to start thinking about the issue: http://en.wikipedia.org/wiki/Automatic_number_plate_recognition