1. HSV颜色过滤

　　HSV颜色模型，共色调、饱和度、值三个参数

  　　H是色调，S是饱和度， S = 0时，只有灰度，V是明度

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:#ESC键退出
        break
cv.destroyAllWindows()

　　inRange() 将保留范围内的颜色通道，其余均置0

　　将RGB转为HSV

>>> green = np.uint8([[[0,255,0 ]]])
>>> hsv_green = cv.cvtColor(green,cv.COLOR_BGR2HSV)
>>> print( hsv_green )
[[[ 60 255 255]]]

　　[H-10, 100,100] and [H+10, 255, 255] 作为the lower bound和 upper bound 

　　imread的参数

　　plt xticks用法