OpenCV 图像的几何变换

一、图像缩放

1.API

cv2.resize(src, dsize, fx=0,fy=0,interpolation = cv2.INTER_LINEAR)

参数：

①src ：输入图像

②dsize：绝对尺寸

③fx，fy：相对尺寸

④interpolation：插值方法

2.代码演示

import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt

img = cv.imread('Genshin.jpeg', -1)
cv.imshow('image', img)
[rows, cols] = img.shape[:2]
res_1 = cv.resize(img, (2*cols, 2*rows), interpolation=cv.INTER_CUBIC)
cv.imshow('image', res_1)
cv.waitKey()
res_2 = cv.resize(img, None, fx=0.5, fy=0.5)
cv.imshow('image', res_1)
cv.waitKey()

二、图像平移

1.API

cv2.warpAffine(img, M, dsize)

参数：

①img：输入图像

②M：2×3移动矩阵，为np.float32类型

③dsize：输出图像的大小

2.代码演示

import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt

img = cv.imread('Genshin.jpeg', -1)
cv.imshow('image', img)
[rows, cols] = img.shape[:2]
M = np.float32([[1, 0, 100], [0, 1, 50]])
dst = cv.warpAffine(img, M, (cols, rows))
cv.imshow('image', dst)
cv.waitKey()

三、图像旋转

1.API

cv2.getRotationMatrix2D(center, angle, scale)
cv.warpAffine()

参数：

①center：旋转中心

②angle：旋转角度

③scale：缩放比例

返回值：

M：旋转矩阵

2.代码演示

import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt

img = cv.imread('Genshin.jpeg', -1)
cv.imshow('image', img)
[rows, cols] = img.shape[:2]
M = cv.getRotationMatrix2D((cols/2, rows/2), 120, 1)
dst = cv.warpAffine(img, M, (cols, rows))
cv.imshow('image', dst)
cv.waitKey()

四、仿射变换

1.API

cv2.getAffineTransform()
cv2.warpAffine()

2.代码演示

import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt

img = cv.imread('Genshin.jpeg', -1)
cv.imshow('image', img)
[rows, cols] = img.shape[:2]
pts1 = np.float32([[50, 50], [200, 50], [50, 200]])
pts2 = np.float32([[100, 100], [200, 50], [100, 250]])
M = cv.getAffineTransform(pts1, pts2)
dst = cv.warpAffine(img, M, (cols, rows))
cv.imshow('image', dst)
cv.waitKey()

五、透射变换

1.API

cv2.getPerspectiveTransform()
cv2.warpPerspective()

2.代码演示

import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt

img = cv.imread('Genshin.jpeg', -1)
cv.imshow('image', img)
img = cv.resize(img, None, fx=0.5, fy=0.5)
[rows, cols] = img.shape[:2]
pts1 = np.float32([[56, 65], [368, 52], [28, 138], [389, 390]])
pts2 = np.float32([[100, 145], [300, 100], [80, 290], [310, 300]])
T = cv.getPerspectiveTransform(pts1, pts2)
dst = cv.warpPerspective(img, T, (cols, rows))
cv.imshow('image', dst)
cv.waitKey()

六、图像金字塔

1.API

cv2.pyrUp(img) #对图像进行上采样
cv2.pyrDown(img) #对图像进行下采样

2.代码演示

import cv2 as cv
import numpy as np
import matplotlib.pyplot as plt

img = cv.imread('Genshin.jpeg', -1)
cv.imshow('image', img)
img = cv.pyrDown(img)
img = cv.pyrDown(img)
img = cv.pyrDown(img)
cv.imshow('image', img)
cv.waitKey()