How can we know the camera sensor size from the calibration matrix?
I already have the calibration matrix. But the focal length is in pixels form.
The "focal length" in the calibration matrix is not actually expressed in pixels. It is in fact a ratio that relates the sensor size in the real world to the size of a pixel in the image. It relates the focal length of the lens to distances in the image using a scaling factor in each dimension. More details in this article.
As Zaphod says, you can get a decent approximation combining the calibration matrix with a known focal length for the lens in mm.
A more precise method: open the box, read the serial type number of the CCD, look it up on the interwebs. There are only a handful of CCD manufacturers, and they all publish their spec sheets on the web. Here is an example.
来源：https://stackoverflow.com/questions/16952880/use-calibration-matrix-to-know-ccd-sensor-size