已知这些png图片都是以黑色为背景，以rgb(128,0,0)为mask的图片。这个怎么注解图片？？？

[gg22mm]

已知这些png图片都是以黑色为背景，以rgb(128,0,0)为mask的图片。这个怎么注解图片？？？

import cv2
import numpy as np

ann_img = np.zeros((30,30,3)).astype('uint8')
ann_img[ 3 , 4 ] = 1 # this would set the label of pixel 3,4 as 1
ann_img[ 0 , 0 ] = 2 # this would set the label of pixel 0,0 as 2

cv2.imwrite( "ann_1.png" ,ann_img )

上面的代码怎么写呢？？？