Wrong distortion parameters in camera calibration

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Hope you are doing well. I have calibrated my Raspberry Pi V2 camera using single camera calibrator app in MATLAB. I tried to do everything as per instructions provided here. However, the distortion parameters seem to be incorrect, since when I apply these distortion parameters (i.e., try to undistort the images using
), the image gets cropped and surrounded by barrel-like black borders. For clarification, I have attached a sample image before and after being undistorted.
Ideas are much appreciated!

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Bjorn Gustavsson
Bjorn Gustavsson 2021년 9월 27일
After quickly looking at the amount of distortion noticeable it seems pretty small - open the images in gimp (for example, comercial software also available) and add lines to the edge of the table on the left it is perhaps a small difference corrected for in the undistorted version, but at this resolution it is difficult to tell (you might have raw-images with higher resolution). When I try to image the difference between the grayscale version (gIm1 = double(rgb2gray(Im1))); etc) it is still difficult to tell. The undistortion is just a re-interpolation of the image as it would've been captured with an ideal plain pin-hole camera (no half-spherical beads only the pin-hole). Therefore, for pincushion-distortion images the lines-of-sight along edges of the ideal plain pinhole-cameras fall outside the field-of-view of pincushion-distorting optics, and the image intensities of the corresponding pixels are set to zero.
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Mohammad Hussein Yoosefian
Mohammad Hussein Yoosefian 2021년 9월 27일
Thank you for your fast reply. Good tip. The next step is to detect Harris corners. If I use the raw undistorted image, the most powerful corners would always locate at the black border (due to high intensity difference between dark and bright pixels of the border). Therefore, I think the best measure to take is to crop the undistorted image. Appreciate your consideration!

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