初识OpenCV-Python - 003:Mouse as a paint-brush

Posted 2020-11-16 august2019

此次学习了如何在OpenCV中使用鼠标事件。主要使用cv2.setMouseCallback()函数来调用鼠标事件。

首先，鼠标有如下事件：

>>> import cv2
>>>events = [i for i in dir(cv2) if ‘EVENT‘ in i]
>>>print(events)
[‘EVENT_FLAG_ALTKEY‘, ‘EVENT_FLAG_CTRLKEY‘, ‘EVENT_FLAG_LBUTTON‘, ‘EVENT_FLAG_MBUTTON‘, ‘EVENT_FLAG_RBUTTON‘, ‘EVENT_FLAG_SHIFTKEY‘, ‘EVENT_LBUTTONDBLCLK‘, ‘EVENT_LBUTTONDOWN‘, ‘EVENT_LBUTTONUP‘, ‘EVENT_MBUTTONDBLCLK‘, ‘EVENT_MBUTTONDOWN‘, ‘EVENT_MBUTTONUP‘, ‘EVENT_MOUSEHWHEEL‘, ‘EVENT_MOUSEMOVE‘, ‘EVENT_MOUSEWHEEL‘, ‘EVENT_RBUTTONDBLCLK‘, ‘EVENT_RBUTTONDOWN‘, ‘EVENT_RBUTTONUP‘]

然后使用鼠标事件画图code:

import cv2
import numpy as np

drawing = False # true if mouse is pressed
mode = True # if True, draw rectangle. Press ‘m‘ to toggle to curve
ix,iy = -1,-1

# mouse callback function
def draw_circle(event,x,y,flags,param): #draw_circle函数需要5个函数，所以即使这里并没有使用到flags和param，我们还是要加上它
    global ix,iy,drawing,mode

    if event == cv2.EVENT_LBUTTONDOWN: #如果按下了鼠标，那么将drawing设置为True，从而开始画图
        drawing = True
        ix,iy = x,y

    elif event == cv2.EVENT_MOUSEMOVE: #如果移动鼠标，并且鼠标是按下的状态，那么就开始画图,如果mode是True，那么画矩形，否则画圆形
        if drawing == True:
            if mode == True:
                cv2.rectangle(img,(ix,iy),(x,y),(0,255,0),-1)
            else:
                cv2.circle(img,(x,y),5,(0,0,255),-1)

    elif event == cv2.EVENT_LBUTTONUP: #如果释放鼠标左键，那么不是画图状态
        drawing = False

img = np.zeros((512,512,3), np.uint8) #设置画布
cv2.namedWindow(‘image‘) 
cv2.setMouseCallback(‘image‘,draw_circle) #引用鼠标回调函数

while(1): #一直循环
    cv2.imshow(‘image‘,img)
    k = cv2.waitKey(1) & 0xFF
    if k == ord(‘m‘): #按下m改变画图类型
        mode = not mode
    elif k == 27: #按下Esc退出程序
        break

code结果: