How to calibrate the Kinect camera?

Question

Camera calibration is the process of estimating intrinsic and/or extrinsic parameters. Intrinsic parameters deal with the camera's internal characteristics, such as, its focal length, skew, distortion, and image center. Extrinsic parameters describe its position and orientation in the world. Knowing intrinsic parameters is an essential first step for 3D computer vision, as it allows you to estimate the scene's structure in Euclidean space and removes lens distortion, which degraces accuracy.

I'm using the Kinect for Computer Vision but I need to calibrate it. I've already read some articles about Kinect calibration but I didn't understand very clearly.

I want to start from nothing. Because I need to know how the calibration is done.

How do I do this?

Thanks.

Answer 1

The Kinect is slightly different than your standard camera. There is a customized toolbox here http://www.ee.oulu.fi/~dherrera/kinect/

I'd suggest your read the paper and try to understand what calibration is.

In very simplistic terms you need calibration so that other geometric algorithms can work. The vast majority of geometry-based algorithms in vision assume the pinhole camera model. That is, the center of the camera is a tiny pinhole and rays reflecting off of objects travel in straight lines.

However, a pinhole camera is not practical to manufacture. You can make a pinhole camera at home, but the image quality won't be good.

People use lenses to deal with this. But, lenses are imperfect and they have distortion.

Distortion means that pixel coordinates do not correspond to straight lines anymore. So, many of the algorithms fail to compute the right thing.

Camera intrinsic calibration corrects the distortion in the lens so that the projection is as close to a pinhole as possible.

The Kinect has two cameras. The RGB camera, and the IR camera. Both are factory calibrated, but you can get better results customized for the sensor you use using the toolbox above.

HTH

Answer 2

Thulio, for calibrating the color camera of Kinect have a look at: camera calibration toolbox. Basically you need to print a chessboard pattern on paper, glue it on a planar surface, take a lot of Kinect color pictures and load it with the toolbox to get your camera parameters. I suspect that somebody else may have done that before you (most Kinects will have the same intrinsic parameters, I guess).