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Phones & BG

Posted By: Henrik Bukkjaer
Date: Friday, 16 April 2010, at 7:22 a.m.

In Response To: Phones & BG (Timothy Chow)

Tim, the PP projection on a wall you mention is a bit difficult. But if I recall correctly, that challenge is due to the fact that you are using a camera to find the laser spot, not because the projection plane and the perceived image plane are different. It's sort of like the challenges Chase is pointing out in his bus examples. You don't know anything about the background, so it's difficult to filter out, your don't know the texture of it, so edge detection will probably not work too well, etc. In Chase's example, you don't even know the shape or color of what you're looking for.

That's not the case with the BG board.

Johnny Lee that I referred to earlier, did the PowerPoint thing with the wii remote, since it's cheap and rely on infrared camera - so if you use an infrared pointer, it will easily be able to filter that out!

As for the different perspectives / planes (when you tilt the camera, or go too close with a zoom), that should be fixed rather straight forward with holography calculations.

The Huff transform I mentioned earlier is really named Hough transform (in cas you were looking for descriptions of it). I think that would work together with edge detection...

So, really, if you can spot the corners of your board, then you should be able to square it up, and use any combination of a wide variety of computer vision techniques to locate the checkers. (Especially if you already know the color of the checkers).

I guess you'd find all you need to do this, in the OpenCV library.

Anyway, I've NOT really given too much thought into this, so I might be off. But I just think, if your camera (and a hell of a lot of image programs) can detect red eyes in a photo, then it should be fairly easy to spot a known shape (which is also round) on a known background.

/Henrik

A few links to what I've been referring to:

http://en.wikipedia.org/wiki/Homography

http://en.wikipedia.org/wiki/Hough_transform

Plane/perspective calculations: http://johnnylee.net/projects/thesis/ (where you will see that the calculations are so fast to perform, that they can be done real time with a moving plane!)

Interactive whiteboard: http://johnnylee.net/projects/wii/ (just because you referred to that power point problem Tim!)

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