How to auto crop a car image to get the license plate

I want this code to be able to crop a number plate within the bounding box. It has to be done manually atm.

Answer 1

[Image Analyst]

Perhaps this demo will help:

http://www.mathworks.com/help/vision/examples/automatically-detect-and-recognize-text-in-natural-images.html?prodcode=VP&language=en

If you get the letters like it shows, then you can use bwconvhull() and regionprops() to get the bounding box of all the letters it found. Then use imcrop() to crop it out.

[robo kit]

The bounding box did detect each letter on the license plate.. But I have to crop out the license plate first, then the bounding box will specifically detect the numbers. I'll try to do as you said. Get the bounding box of all the letters first, then use imcrop() to crop it out.

[Image Analyst]

Be sure to use bwconvhull() first (after individual letter segmentation) otherwise you'll have a whole bunch of bounding boxes - one for each letter - instead of just one for the whole plate.

Answer 2

[Walter Roberson]

That is not possible as phrased. See http://uk.mathworks.com/matlabcentral/answers/232793-how-to-extract-license-plate and read all of the comments.

[Image Analyst]

It's not possible to manually crop a region? Maybe your definition of manual is different than mine. Or maybe I don't understand "It has to be done manually atm." At first I thought he needed to have it done manually while standing at the Automatic Teller Machine, but then I thought that doesn't sound right, so I just ignored the "atm" word.

[Walter Roberson]

The question is "How to auto crop a car image" where "auto" means "automatically". The "atm" is an abbreviation for "at the moment". So the poster is doing the cropping manually at the moment and wants it done automatically. To which I point out that you cannot do that unless you greatly restrict what license plates look like.

[Image Analyst]

Got it. One more reason why I hate textspeak.

[robo kit]

Thanks for clarifying my question, Mr. Roberson. I haven't read the comments yet, but this video shows the program automatically detects the numbers at the license plate. https://www.youtube.com/watch?v=bnQp7cLk7O0

[Walter Roberson]

And does the video show a case where the license plates are in (for example) Persian? And written in black letters on a black license plate that is mounted on a black car?

[Thorsten]

@Walter: You forgot to add: ... and in absolute darkness... Honestly, license plates are meant to be read. I don't think that there is any legal license plate around in the whole wide world with black letters on a black plate, but you may prove me wrong.

[Image Analyst]

I'm not exactly sure how it works but the automatic plate readers attached to the front of police cars might rely on the police car's headlights to illuminate it. Or maybe they have their own light source to shine out in a particular direction (towards parked cars or straight ahead).