Python Opencv提取图片中某种颜色组成的图形的方法

import cv2
import matplotlib.pyplot as plt
imagepath = r'tear/11.jpg'
image = cv2.imread(imagepath)
height,width,channel = image.shape
for i in range(height):
  for j in range(width):
    b,g,r = image[i,j]
    if((r-b)>30 and (r-g)>30): #对蓝色进行判断，30不错
      b=0
      g=0
      r=0
    else:
      b=255
      g=255
      r=255
        
    image[i,j]=[r,g,b]
plt.figure(figsize=(20,10))
plt.imshow(image)
plt.show()