How to improve stereo camera calibration?

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Priya on 10 Feb 2016
Commented: Priya on 23 Feb 2016
Hi, I am working on 3D reconstruction. I am using logitech c615 web cameras fixed at distance of 5.5 cm. The distance between the cameras and checkboard patterns is approximately 80 cms. while using stereo calibration app for finding the parameters, mean projection error was 0.21 pixel. But the rectified images come as blank with some parts on the corners. When tried showing with output view as full, it gives the error as memory out... The rectified images appear as below:
</matlabcentral/answers/uploaded_files/45082/rectified%20image%20in%20app.png> The calibration images are attached hereby. (Already posted a q for the same concern.Thanks for ur help Dima . I have tried using first camera being on left of the second. and also tried with distance between the cam and target being larger. I got the result as above)
Thanks for your help in adv!!!

Accepted Answer

Dima Lisin
Dima Lisin on 10 Feb 2016
Edited: Dima Lisin on 10 Feb 2016

Hi Priya,

To fix this problem you have to take more calibration images with the checkerboard close to the edges of the image. It would also be good to take images of the checkerboard at varying distances.

In the images you have the checkerboard is mainly in the center, so that you do not have any points close to the top and the bottom of your field of view. As a result, you do not get a good estimate of the distortion coefficients.

I tried a simple experiment. I used only the left images to calibrate the left camera separately, using the Camera Calibrator app. Then I undistorted one of the images using the undistortImage function and setting the output view to 'full'. This is what I got:

The warping you see indicates that you need to have more data points to get a better estimate of the lens distortion. And that means taking more images. Generally, this is a good way to see if you have accurate calibration. Even if you have low reprojection errors, you may have problems like this, when you do not have good coverage of the field of view.

Priya on 23 Feb 2016
Hi Dima,
I have mailed the calibration images.Thank you in advance.

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