Matlab detectCheckerboardPoints imperfection (vs. opencv), how to improve it's accuracy?

Question

Chen ZHANG 2016-12-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/316315-matlab-detectcheckerboardpoints-imperfection-vs-opencv-how-to-improve-it-s-accuracy

编辑： Chen ZHANG 2016-12-10

PS: I've posted the same question here: http://stackoverflow.com/questions/41064292/matlab-detectcheckerboardpoints-imperfection

NOTE: For some reason, I have to use the image I posted below. How can I succeed this job in Matlab?

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I'm recently using the Matlab Single Camera Calibration App algorithm to calibrate the camera intrinsics and extrinsics. On finding corners of the chessboard, many times `detectCheckerboardPoints` function of Matlab out performs (accuracy) the opencv api `cv::findChessboardCorners`, yet on some pictures, Matlab behaves strange.

E.g., in the following image, corners between board squares are clear to see, while matlab finds redundant ones on strange places:

1. original image: //there should be 5*8=40 inner corner points

2. corner points found on the undistorted image: //6*9=54 found

3. points found on the original image: //6*10=60...

The matlab code snippet is simple as below:

    img=imread(fn);
    [imUndist, newOrig]=undistortImage(img, cameraParams);
    [pxs, bdsize]=detectCheckerboardPoints(imUndist); %or detect on 'img' directly
    imMarked=insertMarker(imUndist, pxs);
    imshow(imMarked);

4. corners detected with `opencv` (code below) on this image is much precise:

//opencv code:

    Mat img = imread(fpath);
    int ww = 8, hh = 15;
    cv::Size bsz(ww, hh);
    vector<Point2f> ptvec;
    bool found = cv::findChessboardCorners(img, bsz, ptvec, CALIB_CB_ADAPTIVE_THRESH + CALIB_CB_NORMALIZE_IMAGE);
    cv::drawChessboardCorners(img, bsz, ptvec, found);
    imshow("img", img);
    waitKey();