How to plot a probability map in python?

I am not that much expert in python, still learning.

I have a probability map (values between range 0 and 1) 'prop' saved in np.array with the shape (3, 256, 256),

that prob(0,256,256) is the probability of each pixel belonging to class 0 , prob(1,256,256) for class 1 and prob(2,256,256) for class 2.

I tried to plot this:

plt.imshow(prob[1,:,:])
plt.show()

but the output is a black image, I do not see any output. I wanted to plot the image of each class separately. If I am not mistaken this is called heatmap. Could someone please guide me with this? I do not know how to visualize this array.