calibrateCamera - MSFT LifeCam 3000 HD - Sensor Technical Details

asked 2013-06-26 15:17:06 -0600

pistorinoj
183 ●2 ●8 ●18

I am trying to use the calibrateCamera function to calibrate my MSFT LifeCam 3000 HD webcam.

In order to do that, I understand that need to know fx and fy (the focal lengths of both the x and y axes).

However, I am having a tough time finding that information out.

The only technical data from the spec sheet appears to be:

1) "fixed focus from 0.3 to 1.5mm";

2) "Field of View - 68.5 deg diagonal field of view".

The camera does have a 16:9 aspect ratio.

There is no information about the size of the sensor, manufacturer, etc.

I even tore one of these cameras down but the sensor is tiny and there are no markings on the chip itself.

I am following this example for the calibration process, which I have seen recommended.

Am I doing this right? Any idea on how to get the information?

Thanks for any help.

answered 2013-06-26 18:45:14 -0600

Mathieu Barnachon

4678 ●18 ●53 http://www.math-barnac...

If you used OpenCV to calibrate your camera, you don't need to know the focal, it's calibrateCamera (or findIntrinsicParameters) that will give it to you. I quickly read the tutorial, which is quite similar to the calibration sample in OpenCV, and you only have to provide the number of corners in your chessboard.

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Are you sure? In that tutorial, the following lines appear:

We modify the intrinsic matrix with whatever we do know. The camera’s aspect ratio is 1 (that’s usually the case… If not, change it as required). intrinsic.<float>(0)[0] = 1; intrinsic.<float>(1)[1] = 1; Elements (0,0) and (1,1) are the focal lengths along the X and Y axis.

They are modifying the cameraMatrix. The OpenCV 2.4.5 Camera Calibration and 3D Reconstruction documentation says the same thing about needing to specify some of fx, fy, etc.

pistorinoj ( 2013-06-26 19:17:03 -0600 )edit

The cameraMatrix parameter specify that you have to provide fx/fy only if you used one of these flags: CV_CALIB_USE_INTRINSIC_GUESS or CV_CALIB_FIX_ASPECT_RATIO. It means that you don't want to find intrinsic parameters of your camera (because you already know them).

Mathieu Barnachon ( 2013-06-26 19:48:43 -0600 )edit

Thanks for clearing that up. It is still unclear if the whole thing is working right but at least it is not this issue any more. Thanks again.

pistorinoj ( 2013-06-26 22:34:02 -0600 )edit

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