本代码python opencv运行，用鼠标在原图上面依次左击点三个点，左上，左下，右下。然后设定固定窗口大小，比如384128大小。
就是把在原图上面点击的三个点映射到384128大小图像上来。不管你原图选中多大面积的图像都会映射到我们设定的大小上面来。
这里就是仿射变换的原理映射。通过三对点映射关系求得仿射变换矩阵。然后通过矩阵来弄图像。
这里需要注意的是大图上面的点可以映射到截取的小图上面，同样的，小图上面的点也可以映射到大图上！
下面代码就是：
import cv2
import numpy as npdef OnMouseEvent( event, x, y, flags, param):global lbtDownPosglobal posglobal pointListimg = paramignoreEvent = [cv2.EVENT_MBUTTONDOWN, cv2.EVENT_MBUTTONUP, cv2.EVENT_MBUTTONDBLCLK, cv2.EVENT_MOUSEWHEEL,cv2.EVENT_MOUSEHWHEEL,cv2.EVENT_MOUSEMOVE,cv2.EVENT_LBUTTONDBLCLK, cv2.EVENT_RBUTTONDBLCLK, cv2.EVENT_RBUTTONDOWN, cv2.EVENT_RBUTTONUP] # 需要忽略的鼠标事件needRecordEvent = [ cv2.EVENT_LBUTTONDOWN, cv2.EVENT_LBUTTONUP] # 需要记录当前信息的鼠标事件if event == cv2.EVENT_LBUTTONDOWN:pos = (x,y)print("---1 pos 》OnMouseEvent EVENT_LBUTTONDOWN:",pos)n = len(pointList)if True:if len(pointList) <= 3:pointList.append(pos)cv2.putText(img, '.', (x - 10, y), fontFace=cv2.FONT_HERSHEY_SIMPLEX, fontScale=3, color=(255, 0, 0))cv2.putText(img, f'select point{n}:({x},{y})', (x + 20, y), fontFace=cv2.FONT_HERSHEY_SIMPLEX,fontScale=0.3, color=(255, 0, 0))def getPoint(imgfile):global posglobal pointListpointList = []img = cv2.imread(imgfile)cv2.putText(img, 'https://www.cnblogs.com/yanghailin/', (100, 120), fontFace=cv2.FONT_HERSHEY_SIMPLEX,fontScale=0.5, color=(255, 0, 0))imgbak = np.array(img)rows,cols = img.shape[:2]rows = 128cols = 384winName = 'select three point'cv2.namedWindow(winName)cv2.setMouseCallback(winName, OnMouseEvent, img)print("请将要单独放大的部分从其左上角、左下角、右下角分别鼠标左键点击选择三个点，选择后在图像上有提示信息，选择完成后按ESC退出")while True:#通过鼠标左键点击选择三个点，分别代表要映射到左上、左下和右下三个点cv2.imshow(winName, img)ch = cv2.waitKey(100)if ch == 27: breakdestPoint = [(0,0),(0,rows),(cols,rows)]if len(pointList)==3:pts1 = np.float32(pointList)pts2 = np.float32(destPoint)M = cv2.getAffineTransform(pts1, pts2)print("=========M===========")print(M)dst = cv2.warpAffine(imgbak, M, (cols, rows))# b = np.array([cols/2,rows/2,1])# b = np.array([rows / 2, cols / 2, 1])b = np.array([1760 / 2 + 100, 540 / 2 + 40, 1])a = np.matmul(M,b) #a = M * b img384 = M * img1760 --->大图映射到小图cv2.circle(imgbak, (int(b[0]), int(b[1])), 8, (0, 255, 255), -1)cv2.circle(dst, (int(a[0]), int(a[1])), 4, (0, 255, 255), -1)# M_i = []M_i = cv2.invertAffineTransform(M)b = np.array([384 / 2 + 0, 128 / 2 + 0, 1])a = np.matmul(M_i, b) # a = M * b img1760 = M * img384 --->小图映射到大图cv2.circle(dst,(int(b[0]),int(b[1])),8,(255,0,0),-1)cv2.circle(imgbak, (int(a[0]),int(a[1])), 12, (255, 0, 0), -1)cv2.imshow(winName, dst)cv2.imshow("src", imgbak)ch = cv2.waitKey(0)else:print("没有选择足够的点")getPoint("/data_1/1.jpeg")鼠标左击分别点左上，左下，右下。然后按esc键。
下图可以看到我们在原图上面设定的点可以正确映射到小图，反之也是可以。都能对应上。