鼠标事件：
首先创建一个鼠标回调函数，当鼠标事件发生时触发执行。鼠标事件可以是与鼠标相关的任何事，如left-button down, left-button up, left-button double-click等对每个鼠标事件，它都会给出发生时坐标（x,y）。有了这些事件和坐标，可以通过鼠标对图像进行各种处理。
列出所有的可行事件
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']
'''创建鼠标回调函数有特定格式，不同的回调函数只有功能不同。
示例一：下列假设我们的鼠标事件双击时是画个圆,且显示出位置坐标。
# -*- coding: utf-8 -*-import cv2
import numpy as np# mouse callback function
def draw_circle(event, x, y, flags, param):if event == cv2.EVENT_LBUTTONDBLCLK:cv2.circle(img, (x,y), 10, (200,230,180,0.1),-1)cv2.putText(img, '(' + str(x) + ',' + str(y) + ')',org=(x+10,y+10),fontFace=cv2.FONT_HERSHEY_SIMPLEX,fontScale=0.3,color=(0,0,255))# create a image, a window and bing the function to window
img = cv2.imread('../image/girl001.png')
cv2.namedWindow('image',cv2.WINDOW_NORMAL)
cv2.setMouseCallback('image', draw_circle)while True:cv2.imshow('image', img)if cv2.waitKey(30) & 0xFF == 27:break
cv2.destroyAllWindows()
示例而：拖动鼠标画图
import cv2
import numpy as npdrawing = 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 drawing(event,x,y,flags,param):global ix,iy,drawing,modeif event == cv2.EVENT_LBUTTONDOWN:drawing = Trueix,iy = x,yelif event == cv2.EVENT_MOUSEMOVE:if drawing is True:if mode is 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:drawing = Falseif mode is True:cv2.rectangle(img,(ix,iy),(x,y),(0,255,0),-1)else:cv2.circle(img, (x, y), 5, (0, 0, 255), -1)img = cv2.imread('../image/girl001.png')
cv2.namedWindow('image')
cv2.setMouseCallback('image',drawing)while True:cv2.imshow('image',img)k = cv2.waitKey(1) & 0xFFif k == ord('m'):mode = not modeelif k == 27:break
cv2.destroyAllWindows()
