Cv2.fillpoly coco annotator segment coordinate conversion to mask image

The following implements a split single channel mask Image generation .
One 、 About arr
1, arr Is a polygonal x y Coordinate array,
[144.7, 134.2] Is a point of this polygon x y coordinate .
arr2 It's from another polygon x y Coordinate array.
2, The data type should be set to np.int32, Otherwise, it will report a mistake .
3, Pass in fillPolly Add brackets before making parameters , Otherwise, it will report a mistake .
Two 、 About fillPoly
fillPoly Of color Parameters , If it is to generate a single channel , Just fill in the number ,
(255,0,0) No mistake. , But easy to follow 3 Channel confusion .
cv2 Of color yes brg The order of .
3、 ... and 、 About channel
We must unify ,
The generated image is a single channel ,
When reading in, it is also a single channel reading .
If it's generated 3 passageway ,
Read in is a single channel read in ,
The number read in will be wrong .

import numpy as np
import cv2
import os

arr = np.array([[144.7, 134.2], [185.5, 132.3], [183.9, 149.6], [142.1, 150.0], [141.7, 143.0], [144.7, 137.3]], dtype=np.int32)
arr2 = np.array([[140.9, 183.4], [186.6, 181.1], [186.6, 188.8], [188.9, 198.4], [196.6, 220.3], [197.0, 236.4], [192.0, 246.0], [190.8, 255.2], [154.0, 257.9], [147.0, 216.8], [140.9, 198.0], [141.3, 183.8]], dtype=np.int32)
h, w = 288, 384
pth = r"F:\vscode_files\project\segment_side"
mask = np.zeros((h, w), dtype=np.int32)
cv2.fillPoly(mask, [arr], color=255)
cv2.fillPoly(mask, [arr2], color=255)
#  This sentence can also be used in the above two lines  cv2.fillPoly(mask, [arr, arr2], color=255)
cv2.imwrite(os.path.join(pth, "2400.png"), mask)

Single channel read in code ：

mask_img = cv2.imread(r"F:\vscode_files\project\segment_side\2400.png", cv2.IMREAD_GRAYSCALE)
print(mask_img.shape) # (288, 384)
print(mask_img)
list_ = []
for i in range(h):
    for j in range(w):
        if mask_img[i][j] not in list_:
            list_.append(mask_img[i][j])
print(list_)

output:

(288, 384)
[[0 0 0 ... 0 0 0]
 [0 0 0 ... 0 0 0]
 [0 0 0 ... 0 0 0]
 ...
 [0 0 0 ... 0 0 0]
 [0 0 0 ... 0 0 0]
 [0 0 0 ... 0 0 0]]
[0, 255]