Visdom- black MNIST images

Hi, I’m having trouble with using Visdom. The ‘data’ is a minibatch of MNIST.
After calling the method ‘images’,
e.g. ‘viz.images(data.reshape(-1,1,28,28), win=‘images’,opts=dict(title=‘images’))’ ,
the export is full of black images and I cannot figure out why this is happening.

Are you able to visualize these images in e.g. matplotlib?
Also, did you normalize or processed these images in some way?

Yes, I checked the data of dataset with matplotlib.pylot.imshow and it works well, the handwritten number can be shown.
The processing code and export are shown in the uploaded pictures.
(upload://xv6FEc0q0KLJLDECVDhIWajBW1a.png)

sorry, it seems like the export picture has missed.