What is the range of depth information in lab

[LGZY432]

def preprocess_frame(self, rgbd):
    rgb = rgbd[:, :, 0:3]
    d = rgbd[:, :, 3] # 84*84
    d = d[16:-16, :] # crop
    d = d[:, 2:-2] # crop
    d = d[::13, ::5] # subsample
    d = d.flatten()
    d = np.power(d/255.0, 10)
    d = np.digitize(d, [0,0.05,0.175,0.3,0.425,0.55,0.675,0.8,1.01])
    d -= 1 
    return rgb, d

d[0-8] or d[1-9] ?

[student-petercai]

What is the meaning of the depth values after this conversion?