仿射变换:
仿射变换是一种二维坐标到二维坐标之间的线性变换,并保持二维图形的“平直性”。转换前平行的线,在转换后依然平行。如下图:
import cv2
import numpy as np
from matplotlib import pyplot as plt
img = cv2.imread('lena.jpg', 1)
rows,cols,channel = img.shape
pts1 = np.float32([[50,50],[200,50],[50,200]])
pts2 = np.float32([[10,100],[200,50],[100,250]])
M = cv2.getAffineTransform(pts1,pts2)
dst = cv2.warpAffine(img,M,(cols,rows))
plt.subplot(121),plt.imshow(img),plt.title('Input')
plt.subplot(122),plt.imshow(dst),plt.title('Output')
plt.show()
透视变换:
透视变换需要3×3的变换矩阵,直线在变换后还是保持直线。为了构造变换矩阵,你需要输入图像的4个点和对应的要输出图像的4个点;要求这4个点其中3个点不共线。使用cv2.getPerspectiveTransform函数构造透视变换矩阵。代码:
import cv2
import numpy as np
from matplotlib import pyplot as plt
img = cv2.imread('sudu.jpg', 1)
rows,cols,ch = img.shape
pts1 = np.float32([[56,65],[368,52],[28,387],[389,390]])
pts2 = np.float32([[0,0],[300,0],[0,300],[300,300]])
M = cv2.getPerspectiveTransform(pts1,pts2)
dst = cv2.warpPerspective(img,M,(300,300))
plt.subplot(121),plt.imshow(img),plt.title('Input')
plt.subplot(122),plt.imshow(dst),plt.title('Output')
plt.show()
还可以参考:仿射变换和透视变换
还可以用下面代码鼠标获取四个点进行仿射变换:
# -*- coding: utf-8 -*-
import numpy as np
import cv2
def gen_point(event,x,y,flags,param):
if event == cv2.EVENT_LBUTTONDBLCLK:
print (x,y)
# img = np.zeros((512,512,3),np.uint8)
img = cv2.imread("lp.jpg")
cv2.namedWindow('image', 2)
cv2.setMouseCallback('image',gen_point)
while(1):
cv2.imshow('image',img)
if cv2.waitKey(20) & 0xFF == 27:
break
cv2.destroyAllWindows()