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.

sorry, it seems like the export picture has missed.