def cvt_tform_mat_for_cv2(trans):
    """
    Convert Transform Matrix 'trans' into 'cv2_trans' which could be directly
    used by cv2.warpAffine():

            u = src_pts[:, 0]
            v = src_pts[:, 1]
            x = dst_pts[:, 0]
            y = dst_pts[:, 1]
            [x, y].T = cv_trans * [u, v, 1].T

    :param trans: 3x3 np.array, transform matrix from uv to xy
    :returns: cv2_trans: transform matrix from src_pts to dst_pts, could be
    used for cv2.warpAffine(), 2x3 np.array
    """
    cv2_trans = trans[:, 0:2].T

    return cv2_trans