Python getOptimalNewCameraMatrix（）返回roi的（0,0,0,0）

我已经提供了下面所有的代码，以防我遗漏了一个明显的问题。讨论中的片段是最后一行，roi变量返回为（0,0,0,0），我一辈子都不知道为什么。同样的代码在其他程序中似乎运行良好，我做错了什么

import numpy as np
import cv2
import glob

# termination criteria
criteria = (cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_MAX_ITER, 30, 0.001)

# prepare object points, like (0,0,0), (1,0,0), (2,0,0) ....,(6,5,0)
objp = np.zeros((6*7,3), np.float32)
objp[:,:2] = np.mgrid[0:7,0:6].T.reshape(-1,2)

# Arrays to store object points and image points from all the images.
objpoints = [] # 3d point in real world space
imgpoints = [] # 2d points in image plane.

img = cv2.imread('left01.jpg')
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)

# Find the chess board corners
ret, corners = cv2.findChessboardCorners(gray, (7,6),None)


print ret
# If found, add object points, image points (after refining them)

if ret == True:
    objpoints.append(objp)
    cv2.cornerSubPix(gray,corners,(11,11),(-1,-1),criteria) # tutorial was wrong here
    imgpoints.append(corners)

    # Draw and display the corners
    cv2.drawChessboardCorners(img, (7,6), corners,ret) # tutorial was also wrong here
    cv2.imshow('img',img)
    cv2.waitKey(500)
    cv2.destroyAllWindows()

ret, mtx, dist, rvecs, tvecs = cv2.calibrateCamera(objpoints, imgpoints, gray.shape[::-1],None,None)

img = cv2.imread('left12.jpg')
h,  w = img.shape[:2]
newcameramtx, roi=cv2.getOptimalNewCameraMatrix(mtx,dist,(w,h),1,(w,h))