Plot a black-and-white binary map in matplotlib

Question

I\'m using python to simulate some automation models, and with the help of matplotlib I\'m producing plots like the one shown below.

Answer 1

There is an alternative method to Yann's answer that gives you finer control. Matplotlib's imshow can take a MxNx3 matrix where each entry is the RGB color value - just set them to white [1,1,1] or black [0,0,0] accordingly. If you want three colors it's easy to expand this method.

import matplotlib.pyplot as plt
import numpy as np

# Z is your data set
N = 100
Z = np.random.random((N,N))

# G is a NxNx3 matrix
G = np.zeros((N,N,3))

# Where we set the RGB for each pixel
G[Z>0.5] = [1,1,1]
G[Z<0.5] = [0,0,0]

plt.imshow(G,interpolation='nearest')
plt.show()

Answer 2

You can change the color map you are using via the cmap keyword. The color map 'Greys' provides the effect you want. You can find a list of available maps on the scipy website.

import matplotlib.pyplot as plt
import numpy as np

np.random.seed(101)
g = np.floor(np.random.random((100, 100)) + .5)

plt.subplot(211)
plt.imshow(g)
plt.subplot(212)
plt.imshow(g, cmap='Greys',  interpolation='nearest')
plt.savefig('blkwht.png')

plt.show()

which results in: