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OpenCV中的投影变换
source link: https://xugaoxiang.com/2022/07/16/opencv-projective-transform/
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前面介绍的仿射变换(平移、缩放、旋转等)都是在二维空间中进行物体变换，如果是在三维空间中发生了旋转，那么这种变换就是投影变换。投影变换需要先计算投影变换矩阵
cv2.getPerspectiveTransform(src, dst)其中，src 和 dst 都是 4x2 的二维矩阵(ndarray)，每一行都是一个坐标，分别代表左上、右上、左下、右下四个点，数据类型是32位浮点型，函数的返回值就是投影变换矩阵，它是一个 3x3 矩阵。也就是说，src 经过了变换矩阵就得到了 dst
得到了变换矩阵，就可以进行投影变换了，方法是
cv2.warpPerspective(src, M, dsize[, dst[, flags[, borderMode[, borderValue]]]])src：原图M：一个3x3的变换矩阵dsize: 输出图像的尺寸大小
import cv2
import numpy as np
imgname = "lenna.png"
image = cv2.imread(imgname, cv2.IMREAD_COLOR)
height, width = image.shape[:2]
src = np.array([[0, 0], [width-5, 0], [0, height-5], [width-5, height-5]], np.float32)
dst = np.array([[100,100], [width/3, 10], [100, height-5], [width-5, height-5]], np.float32)
M = cv2.getPerspectiveTransform(src, dst)
dst = cv2.warpPerspective(image, M, (width, height), borderValue=125)
cv2.imshow("dst image", dst)
cv2.imshow("original image", image)
cv2.waitKey(0)
cv2.destroyAllWindows()
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