python opencv鼠标事件如何实现画框圈定目标获取坐标信息

# -*- coding: utf-8 -*-
"""
Created on Tue Dec 27 09:32:02 2016

@author: http://blog.csdn.net/lql0716
"""
import cv2
import numpy as np

current_pos = None
tl = None
br = None

#鼠标事件
def get_rect(im, title='get_rect'): # (a,b) = get_rect(im, title='get_rect')
 mouse_params = {'tl': None, 'br': None, 'current_pos': None,
 'released_once': False}

 cv2.namedWindow(title)
 cv2.moveWindow(title, 100, 100)

 def onMouse(event, x, y, flags, param):

 param['current_pos'] = (x, y)

 if param['tl'] is not None and not (flags & cv2.EVENT_FLAG_LBUTTON):
  param['released_once'] = True

 if flags & cv2.EVENT_FLAG_LBUTTON:
  if param['tl'] is None:
  param['tl'] = param['current_pos']
  elif param['released_once']:
  param['br'] = param['current_pos']

 cv2.setMouseCallback(title, onMouse, mouse_params)
 cv2.imshow(title, im)

 while mouse_params['br'] is None:
 im_draw = np.copy(im)

 if mouse_params['tl'] is not None:
  cv2.rectangle(im_draw, mouse_params['tl'],
  mouse_params['current_pos'], (255, 0, 0))

 cv2.imshow(title, im_draw)
 _ = cv2.waitKey(10)

 cv2.destroyWindow(title)

 tl = (min(mouse_params['tl'][0], mouse_params['br'][0]),
 min(mouse_params['tl'][1], mouse_params['br'][1]))
 br = (max(mouse_params['tl'][0], mouse_params['br'][0]),
 max(mouse_params['tl'][1], mouse_params['br'][1]))

 return (tl, br) #tl=(y1,x1), br=(y2,x2)

#读取摄像头/视频，然后用鼠标事件画框 
def readVideo(pathName, skipFrame): #pathName为视频文件路径，skipFrame为视频的第skipFrame帧
 cap = cv2.VideoCapture(0) #读取摄像头
 if not cap.isOpened(): #如果为发现摄像头，则按照路径pathName读取视频文件
 cap = cv2.VideoCapture(pathName) #读取视频文件，如pathName='D:/test/test.mp4'
 c = 1

 while(cap.isOpened()):
 ret, frame = cap.read()
 gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
 if(c>=skipFrame):
  mask = np.zeros(gray.shape, dtype=np.uint8) #掩码操作，该矩阵与图片大小类型一致，为初始化全0像素值，之后对其操作区域赋值为1即可
  if(c==skipFrame):
  (a,b) = get_rect(frame, title='get_rect') #鼠标画矩形框
  img01, img02 = frame, frame
  gray01, gray02 = gray, gray
  else:
  img1, img2 = prev_frame, frame
  gray1, gray2 = prev_frame, frame
  cv2.imshow('frame', frame)
 c = c + 1
 prev_gray = gray
 prev_frame = frame
 if cv2.waitKey(1) & 0xFF == ord('q'): #点击视频窗口，按q键退出
  break
 cap.release()
 cv2.destroyAllWindows()