I am trying to calibrate OpenCv with aim to pull object cordinates from the camera once calibrated using OpenCvSharp.

I have processed my image and as an example see the attached

However, when I run (on the example attached image)

// Detect chessboard corners
Point2f[] corners;
bool found = Cv2.FindChessboardCorners(
    grayImage,
    new Size(numCornersX, numCornersY),
    out corners,
    ChessboardFlags.AdaptiveThresh | ChessboardFlags.FilterQuads
);

found is always being returned as false? I have tried many different values in for numCornersX and numCornersY. I have been currently trying 9 for both in am attempt to see if I can get it to detect anything.

Can anyone advise me how I can proceed with this? I think the hols in the middle is possibly causing issues. Is there any way around this?