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My task is to pin-point where is the plate number in an image. The image does not only contain the plate number. It may contain the whole car or anything. I used gaussian blur then grayscale then contrast then laplacian of gaussian to detect the edges.

Now, I am at loss on how to detect where is the plate number in the image. I am not going to read the license number, just make the system know where is the license number.

Can you direct me to a study regarding this? Or perhaps the algorithm that can be used to do this.

Thank you!

jilles de wit
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Eunichi
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    There seem to be a lot of duplicates about this topic here on SO, just search for license plate: http://stackoverflow.com/questions/981378/how-to-recognize-vehicle-license-number-plate-anpr-from-an-image http://stackoverflow.com/questions/4707607/what-are-good-algorithms-for-vehicle-license-plate-detection – bjoernz Jul 31 '12 at 11:35
  • I've searched but didn't find the first link you gave. Thank you! That is what I am looking for. – Eunichi Jul 31 '12 at 15:16

4 Answers4

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I think a more robust way to tackle this is a train a detector if you have enough training images of the license plate in different scenarios. Few things you can try is Haar cascade classifier in Opencv library. It does a multiscale detection of learned patterns.

Krish
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Using some feature recognition algorithm e.g. SIFT would be a good starting point. Do you need real-time recognition or not? I recommend trying to tighten search space first, for example by filtering out regions from the image (is your environment controlled or not?). There is an article about recognising license plates using SIFT here (I just skimmed it but it looks reasonable).

WebMonster
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You could try edge detection or some form of Hough transforms.

For example, do edge detection and then look for rectangles (or if the images aren't straight on, parallelograms) in the image. If you know that the plates will all be the same shape and size ratios, you can use that to speed up your search.

EDIT:

Found this for you.

Community
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Bill
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License-plates or number plates of vehcles come with 2 striking properties.

  1. They have specified color pattern (Black letters on white, yellow or gray background)
  2. Aspect ratio

These properties can be used to extract only the license plate. First threshold the image using adaptive thresholding. Then find contours in the image with aspect ratio in a close range to standard value. This method should work for most of the cases. You can also try erosion followed by dilation of thresholded image to remove noise.

Abhiram
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