1 调程序中的127可以提取多少颜色，有时候有毛边；

2 png是带透明度的图，有颜色的部分设置透明度255就是完全不透明，原来白色的部分设置透明度0就是完全透明；

python
import cv2
import numpy as np
inputimg = 'minio.png'
thresh=180
img1 = cv2.imread(inputimg, 0)
ret, thresh1 = cv2.threshold(img1, 127, 255, cv2.THRESH_BINARY)
img = cv2.imread(inputimg)
b, g, r = cv2.split(img)
b[thresh1 > thresh] = 0
g[thresh1 > thresh] = 0
r[thresh1 > thresh] = 0
alpha_channel = np.zeros(b.shape, dtype=b.dtype)
alpha_channel[thresh1 < thresh] = 255
img = cv2.merge([b, g, r, alpha_channel])
cv2.imwrite("res.png", img)