python openCV图像处理之角度变换

import cv2  
import numpy as np
img = cv2.imread('demo.jpg')
conners = np.array([[873,1322],[1973,1864],[2645,3152],[857,2568]], dtype = "float32")  #矩形(比如：书)的顶点 tl,tr,br,bl
canvas = np.array([[0,0],[500,0],[500,500],[0,500]], dtype = "float32")      #输出文件的大小
M = cv2.getPerspectiveTransform(conners,canvas) 
result = cv2.warpPerspective(img,M,(0,0))
cv2.imshow("img", result) 
cv2.waitKey(0)