How to find pixel co-ordinates of corners of a square pattern?

This may not be a programmi开发者_如何学编程ng related but possibly programmers would be in the best position to answer it.

For camera calibration I have a 8 x 8 square pattern printed on sheet of paper. I have to manually enter these co-ordinates into a text file. The software would then pick it up from there and compute the calibration parameters.

Is there a script or some software that I can run on these images and get the pixel co-ordinates of the 4 corners of each of the 64 squares?

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You can do this with a traditional chessboard pattern (i.e. black and white squares with no gaps) using cvFindChessboardCorners(). You can read more about the function in the OpenCV API Reference and see some sample code in O'Reilly's OpenCV Book or elsewhere online. As an added bonus, OpenCV has built-in functions that calculate the intrinsic parameters of the camera and an array of extrinsic parameters for the multiple views of a planar calibration object.

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I would:

• apply threshold and get binarized image.
• apply SobelX filter to image. You get an image with the vertical lines. This belong to the sides of the squares that are almost vertical. Keep this as image1.
• apply SobelY filter to image. You get an image with the horizontal lines. This belong to the sides of the squares that are almost horizontal. Keep this as image2.
• make (image1 xor image2). You get a black image with white pixels indicating the corner positions.

Hope it helps.

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I'm sure there are many computer vision libraries with varying capabilities and licenses out there, but one that I can remember off the top of my head is ARToolKit, which should be able to recognize this pattern. And if that's not possible, it comes with a set of very good patterns that are tailored so that they can be recognized even if they're partially obscured.

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I don't know ARToolKit (although i've heard a lot about it) but with OpenCV this processing is trivial.