License Plate Blurring

[Otheus Shelling]

Thanks to the project devs for making this unique tool available. 

How might I use it to automate blurring of plates? I have hundreds of videos from my helmet-cam, but in order for me to publish them (ie, YouTube) publically, the (European) laws require I blur-out any license plates (and faces, but those are rare, and relatively easy with YouTube). 

I imagine I can use the detect-region option and feed the output into another program that overlays a blur or mask. But I've no idea where to get started.

[Matt]

Yes, you can run OpenALPR as a library.  The results that come back will contain the x/y location of each detected plate.  You can use this to add blurring to the video output.

You may need to interpolate the position of the plate between frames.  If, for example, OpenALPR detects the plate in 23 frames out of 25, those 2 frames still should get blurred.

[Otheus Shelling]

Thanks, that gets me a step closer.  Do I get x/y as a center with a radius? Or some kind of rough polygon?  If there are multiple plates, do I get multiple pairs for reach frame? 

Any chance you can tell me what kind of software I would fee that data into?

[Matt]

Yes, you would get the x/y coordinates of the license plate polygon (top-left, top-right, bottom-right, bottom-left).  Multiple plates will return multiple results for each frame.

If I were doing this, I'd probably:

1. Analyze the video with OpenALPR and get results for each frame
2. Group the similar plates together across frames based on similarity of text content
3. Interpolate the positions of those plate groups for all frames (e.g., OpenALPR sees the plate in frame 1, 2, 3, and 5, this would fill in the position for frame 4)
4. Do a gaussian blur or some other visual effect over the polygon, and save the frames
5. Remix with FFMPEG