calibrator.py 文件源码

def _get_corners(img, board, refine = True, checkerboard_flags=0):
    """
    Get corners for a particular chessboard for an image
    """
    h = img.shape[0]
    w = img.shape[1]
    if len(img.shape) == 3 and img.shape[2] == 3:
        mono = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    else:
        mono = img
    (ok, corners) = cv2.findChessboardCorners(mono, (board.n_cols, board.n_rows), flags = cv2.CALIB_CB_ADAPTIVE_THRESH |
                                              cv2.CALIB_CB_NORMALIZE_IMAGE | checkerboard_flags)
    if not ok:
        return (ok, corners)

    # If any corners are within BORDER pixels of the screen edge, reject the detection by setting ok to false
    # NOTE: This may cause problems with very low-resolution cameras, where 8 pixels is a non-negligible fraction
    # of the image size. See http://answers.ros.org/question/3155/how-can-i-calibrate-low-resolution-cameras
    BORDER = 8
    if not all([(BORDER < corners[i, 0, 0] < (w - BORDER)) and (BORDER < corners[i, 0, 1] < (h - BORDER)) for i in range(corners.shape[0])]):
        ok = False

    if refine and ok:
        # Use a radius of half the minimum distance between corners. This should be large enough to snap to the
        # correct corner, but not so large as to include a wrong corner in the search window.
        min_distance = float("inf")
        for row in range(board.n_rows):
            for col in range(board.n_cols - 1):
                index = row*board.n_rows + col
                min_distance = min(min_distance, _pdist(corners[index, 0], corners[index + 1, 0]))
        for row in range(board.n_rows - 1):
            for col in range(board.n_cols):
                index = row*board.n_rows + col
                min_distance = min(min_distance, _pdist(corners[index, 0], corners[index + board.n_cols, 0]))
        radius = int(math.ceil(min_distance * 0.5))
        cv2.cornerSubPix(mono, corners, (radius,radius), (-1,-1),
                                      ( cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 30, 0.1 ))

    return (ok, corners)