活动图与状态图：UML中流程图的精细化表达——专业解析系统动态性与状态变迁

在日常生活，总是离不开火，有时候我们需要预防火灾发生，但是我们又不可能一直盯着，这时候我们就需要一款程序帮我们盯着，一旦发生火灾从而告知我们，今天就带大家编写这么一款应用。

安装需要的库

pip install opencv-python

代码实现

import cv2         # Library for openCV

# To access xml file which includes positive and negative images of fire. 
# (Trained images) File is also provided with the code.
fire_cascade = cv2.CascadeClassifier('fire_detection.xml') 

vid = cv2.VideoCapture(0)

while(True):
    # Value in ret is True # To read video frame
    ret, frame = vid.read() 
    # To convert frame into gray color
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY) 
    # to provide frame resolution
    fire = fire_cascade.detectMultiScale(frame, 1.2, 5) 

    ## to highlight fire with square 
    for (x,y,w,h) in fire:
        cv2.rectangle(frame,(x-20,y-20),(x+w+20,y+h+20),(255,0,0),2)
        roi_