NWPU Dataset --- How to reproduce luminance level labels?

[genesis9329]

Could you share the official code about how to assign luminance level label, please?
I tried to reproduce luminance level label of 0113.jpg according to your paper:

import cv2
import numpy as np

img_path = "/home/datasets/NWPU-Crowd/images/0113.jpg"
img = cv2.imread(img_path) #shape=(H,W,C)

yuv = cv2.cvtColor(img, cv2.COLOR_BGR2YUV)
yuv_normalized = yuv.astype(np.float32)/255.0
lumin = np.mean(yuv_normalized[:,:,0])
if lumin <= 0.25:
    label = 0
elif lumin <= 0.5:
    label = 1
elif lumin <= 0.75:
    label = 2

print("lumin =", lumin)
print("label =", label)

the output is "lumin = 0.21811360026165477", which should be assigned label "0” according to the paper, but in train.txt, "1" is assigned to 0113.jpg.
And many other images have a similar problem, so I'm wondering whether my code is wrong or threshold settings are different.