Marin's profile - activity

I cannot really see a difference in the undistorted output whether I use one calibration result or the other, so you were right!

That's good to hear. I'll do some extra testing to see if the rectified image is indeed correct and accept your answer if that is the case. Thanks!

I'm trying to calibrate the camera of a Blackberry Playbook tablet. To do this I shot several videos of both a chessboard and an asymmetric circles pattern. I film the pattern from different angles and sides. Using OpenCV, I find a frame that contains the pattern and then I skip a number of frames (equivalent to 0.25-1.0 seconds) for the next input. I use a total of 30 frames. This consistently gives me a reprojection error of about 0.24-0.30, which is reasonable I guess.

My problem is that when I change the amount of frames skipped or the calibration pattern the distortion coefficients change dramatically. I thought it might be caused by motion blur of the camera, but I can't really detect it with my own eyes and I do not move the camera quite gently.

What could I be doing wrong?

Here are some calibration results, taken from output .yml files written using FileStorage:

distCoeffs: [ 7.8525429419470660e-02, -3.0960261342412626e-01, 
             -8.6524434042007194e-04, -1.5106802929380169e-03,
              2.4943420525237567e-01 ]
reprojectionError: 2.5980283849938213e-01

distCoeffs: [ 9.5072469884162333e-02, -4.0909425759139262e-01,
             -1.4098479752338933e-03, -8.5000416228384647e-03,
             4.9234810766112463e-01 ]
reprojectionError: 2.9590490979407219e-01

distCoeffs: [ 8.4964364149716379e-02, -2.6207341751103475e-01,
             -4.4505493959335414e-04, -5.4369272625535434e-03,
              4.7645565934149210e-02 ]
reprojectionError: 2.4693283075662995e-01

distCoeffs: [ -2.4401111960459070e-03, 7.7251179587715735e-01,
              -3.4754734701746902e-03, -5.5816510106682163e-03,
              -3.8066475946718032e+00 ]
reprojectionError: 2.4246869857561970e-01

I call calibrateCamera a total of 4 times with the following flags (I thought this would increase the accuracy, but the results don't change between calibration passes):

flags = 0;
flags = CALIB_USE_INTRINSIC_GUESS | CALIB_FIX_PRINCIPAL_POINT;
flags = CALIB_USE_INTRINSIC_GUESS | CALIB_FIX_ASPECT_RATIO;
flags = CALIB_USE_INTRINSIC_GUESS;