How to save grayscale image in Pytorch?

Question

I want to save grayscale image in Pytorch, each image has four gray values, 0 , 60 , 120 and 180 . I try the following way to save images, but the saved image is not I expected.

for i, (inputs) in enumerate(test_generator):
    pred = modelPl(inputs.float()).detach()
    fig,ax = plt.subplots(1,1,figsize = (5,5))
    ax.imshow(pred[0,:,:], cmap = "gray")
    print(pred.shape)
    torchvision.utils.save_image(pred, saveTestPath + 'img_{0}.png'.format(i)) 

Output: torch.Size([400, 400])

Expected image:

However, the saved picture is not correct as follows:

Answer 1

It might be that torchvision.utils.save_image requires values to be in range 0 to 1. Your images have values which are greater than 1 and hence the problem.

You can check this by dividing the tensor by 255 (or some appropriate number). You can also try to set normalize=True and see if it can automatically normalize the data for you.