opencv 颜色空间转换、颜色追踪

opencv 有150种空间转换方法，我们只研究最长用的两种：
1.BGR->灰色 flag=BGR2GRAY
2.BGR->HSV flag=BGR2HSV
函数使用
cvtColor(img,flag)

import cv2 as cv
flags = [i for i in dir(cv) if i.startswith('COLOR_')]
print( flags )  # 查看所有转换模式

在HSV中表示一种颜色比在BGR中更容易

import cv2 as cv
import numpy as np
cap = cv.VideoCapture(0)
while(1):
    # Take each frame
    _, frame = cap.read()
    # Convert BGR to HSV
    hsv = cv.cvtColor(frame, cv.COLOR_BGR2HSV)
    # define range of blue color in HSV
    lower_blue = np.array([110,50,50])
    upper_blue = np.array([130,255,255])
    # Threshold the HSV image to get only blue colors
    mask = cv.inRange(hsv, lower_blue, upper_blue)
    # Bitwise-AND mask and original image
    res = cv.bitwise_and(frame,frame, mask= mask)
    cv.imshow('frame',frame)
    cv.imshow('mask',mask)
    cv.imshow('res',res)
    k = cv.waitKey(5) & 0xFF
    if k == 27:
        break
cv.destroyAllWindows()

参考文献：
https://docs.opencv.org/3.4.3/df/d9d/tutorial_py_colorspaces.html
https://blog.csdn.net/qq_41905045/article/details/81324671