基于python的opencv实现简单的颜色分割

import cv2 as cv
from cv2 import blur
import numpy as np

bird = cv.imread("./img/bird.png")
if bird is None:
    print("路径问题")
else:
    blur = cv.blur(bird,(5,5))
    hsv = cv.cvtColor(blur,cv.COLOR_BGR2HSV)

    low_blue = np.array([55,0,0])
    high_blue = np.array([118,255,255])
    #可实现二值化功能（类似threshold()函数）可以同时针对多通道进行操作
    mask = cv.inRange(hsv,low_blue,high_blue)
    res = cv.bitwise_and(bird,bird,mask=mask)
    cv.imshow("img",res)

cv.waitKey()

不理解的地方： mask = cv.inRange(hsv,low_blue,high_blue)得到黑白图，数值的设置原则是什么

最终得到