How do I convert a numpy array to (and display) an image?

Use plt.imshow to create the figure, and plt.show to display it:

from matplotlib import pyplot as plt
plt.imshow(data, interpolation='nearest')
plt.show()

For Jupyter notebooks, add this line before importing matplotlib:

%matplotlib inline 

For interactive plots in Jupyter [demo], install ipyml pip install ipympl, then use:

%matplotlib widget 

You could use PIL to create (and display) an image:

from PIL import Image
import numpy as np

w, h = 512, 512
data = np.zeros((h, w, 3), dtype=np.uint8)
data[0:256, 0:256] = [255, 0, 0] # red patch in upper left
img = Image.fromarray(data, 'RGB')
img.save('my.png')
img.show()

Note: both these APIs have been first deprecated, then removed.

Shortest path is to use scipy, like this:

# Note: deprecated in v0.19.0 and removed in v1.3.0
from scipy.misc import toimage
toimage(data).show()

This requires PIL or Pillow to be installed as well.

A similar approach also requiring PIL or Pillow but which may invoke a different viewer is:

# Note: deprecated in v1.0.0 and removed in v1.8.0
from scipy.misc import imshow
imshow(data)

Using pillow's fromarray, for example:

from PIL import Image
from numpy import *

im = array(Image.open('image.jpg'))
Image.fromarray(im).show()