Creating a Colormap Legend in Matplotlib

Question

Hi fellow Stackers!

I am using imshow() in matplotlib like so:

import numpy as np
import matplotlib.pyplot as plt
mat = '''SOME MATRIX'''
plt.imshow(mat, origin="lower", cmap='gray', interpolation='nearest')
plt.show()

How do I add a legend showing the numeric value for the different shades of gray. Sadly, my googling has not uncovered an answer :(

Thank you in advance for the help.

Vince

Answer 1

As usual, I figure it out right after I ask it ;). For posterity, here's my stab at it:

m = np.zeros((1,20))
for i in range(20):
    m[0,i] = (i*5)/100.0
print m
plt.imshow(m, cmap='gray', aspect=2)
plt.yticks(np.arange(0))
plt.xticks(np.arange(0,25,5), [0,25,50,75,100])
plt.show()

I'm sure there exists a more elegant solution.

Vince

Answer 2

There's a builtin colorbar() function in pyplot.