Opencv Python 简明教程

OpenCV Python - Handling Mouse Events

OpenCV 能够用一个回调函数来注册各种鼠标相关事件。这用于根据鼠标事件的类型来启动一个特定用户定义的动作。

OpenCV is capable of registering various mouse related events with a callback function. This is done to initiate a certain user defined action depending on the type of mouse event.

Sr.No

Mouse event & Description

1

cv.EVENT_MOUSEMOVE When the mouse pointer has moved over the window.

2

cv.EVENT_LBUTTONDOWN Indicates that the left mouse button is pressed.

3

cv.EVENT_RBUTTONDOWN Event of that the right mouse button is pressed.

4

cv.EVENT_MBUTTONDOWN Indicates that the middle mouse button is pressed.

5

cv.EVENT_LBUTTONUP When the left mouse button is released.

6

cv.EVENT_RBUTTONUP When the right mouse button is released.

7

cv.EVENT_MBUTTONUP Indicates that the middle mouse button is released.

8

cv.EVENT_LBUTTONDBLCLK This event occurs when the left mouse button is double clicked.

9

cv.EVENT_RBUTTONDBLCLK Indicates that the right mouse button is double clicked.

10

cv.EVENT_MBUTTONDBLCLK Indicates that the middle mouse button is double clicked.

11

cv.EVENT_MOUSEWHEEL Positive for forward and negative for backward scrolling.

要根据鼠标事件来调用函数，就必须使用 setMouseCallback() 函数来注册。对应的命令如下所示：

To fire a function on a mouse event, it has to be registered with the help of setMouseCallback() function. The command for the same is as follows −

cv2.setMouseCallback(window, callbak_function)

此函数将事件的类型和位置传递给回调函数以进行进一步处理。

This function passes the type and location of the event to the callback function for further processing.

Example 1

以下代码会在窗口图像背景上发生左键双击事件时绘制一个圆：

Following code draws a circle whenever left button double click event occurs on the window showing an image as background −

import numpy as np
import cv2 as cv
# mouse callback function
def drawfunction(event,x,y,flags,param):
   if event == cv.EVENT_LBUTTONDBLCLK:
      cv.circle(img,(x,y),20,(255,255,255),-1)
img = cv.imread('lena.jpg')
cv.namedWindow('image')
cv.setMouseCallback('image',drawfunction)
while(1):
   cv.imshow('image',img)
   key=cv.waitKey(1)
   if key == 27:
      break
cv.destroyAllWindows()

Output

运行以上程序然后在随机位置双击。将会看到类似的输出：

Run the above program and double click at random locations. The similar output will appear −

mouse events

Example 2

根据用户输入（1、2 或 3）交互式绘制矩形、线或圆：

Following program interactively draws either rectangle, line or circle depending on user input (1,2 or 3) −

import numpy as np
import cv2 as cv
# mouse callback function

drawing=True
shape='r'

def draw_circle(event,x,y,flags,param):
   global x1,x2
   if event == cv.EVENT_LBUTTONDOWN:
      drawing = True
      x1,x2 = x,y
   elif event == cv.EVENT_LBUTTONUP:
      drawing = False
      if shape == 'r':
         cv.rectangle(img,(x1,x2),(x,y),(0,255,0),-1)
      if shape == 'l':
         cv.line(img,(x1,x2),(x,y),(255,255,255),3)
      if shape=='c':
         cv.circle(img,(x,y), 10, (255,255,0), -1)
img = cv.imread('lena.jpg')
cv.namedWindow('image')
cv.setMouseCallback('image',draw_circle)
while(1):
   cv.imshow('image',img)
   key=cv.waitKey(1)
   if key==ord('1'):
      shape='r'
   if key==ord('2'):
      shape='l'
   if key==ord('3'):
      shape='c'

   #print (shape)
   if key == 27:
      break
   cv.destroyAllWindows()

如果按下“1”，将在鼠标左键按下和抬起的坐标之间绘制一个矩形。

On the window surface, a rectangle is drawn between the coordinates of the mouse left button down and up if ‘1’ is pressed.

如果用户选择 2，将使用坐标作为端点绘制一条线。

If user choice is 2, a line is drawn using coordinates as endpoints.

如果选择 3 绘制圆，则会在鼠标抬起事件的坐标处绘制一个圆。

On choosing 3 for the circle, it is drawn at the coordinates of the mouse up event.

在成功执行以上程序后，输出将显示如下图像：

Following image will be the output after the successful execution of the above mentioned program −

mouse event