How to process the array correctly

[Fly_jia]

import numpy as np
from timeit import default_timer as timer

mask = np.load('mask.npy', allow_pickle=True)

cell_mask_new_all = mask[:, :, :].astype(np.uint8)
cell_mask_one = cell_mask_new_all[:,:,186]

cell_mask_two = np.uint8(mask[:, :, 186])


t_1 = timer()
image_cell_mask_one = cell_mask_one*255
t_2 = timer()
print('image_cell_mask_one time:', t_2 - t_1)

t_3 = timer()
image_cell_mask_two = cell_mask_two*255
t_4 = timer()
print('image_cell_mask_two time:', t_4 - t_3)

I found a very interesting question. As you see, I use different code to get Cell_mask_one and Cell_mask_two, but the time of they multiply 255 is very difference.

I can not upload the img, and Write it out by hand。

t_1 = timer()
image_cell_mask_one = cell_mask_one*255
t_2 = timer()
print('image_cell_mask_one time:', t_2 - t_1)
0.04487754100409802

t_3 = timer()
image_cell_mask_two = cell_mask_two*255
t_4 = timer()
print('image_cell_mask_two time:', t_4 - t_3)
0.002681313009816222

The memory of data is almost 898mb，I can't upload here. I put the data at the google drive.
https://drive.google.com/file/d/1LyJxMiW...sp=sharing
Would you help me?Thanks.