Custom Colormap in Python

Question

I would like to create my own custom colour map in python, I looked into some of the online examples and found out the commands

from matplotlib import cm 
import matplotlib.pyplot as plt 
from matplotlib.colors import LinearSegmentedColormap

cdict1 = {'red':   ((0.0, 0.0, 0.0),
                    (0.5, 0.0, 0.1),
                    (1.0, 1.0, 1.0)),

         'green': ((0.0, 0.0, 0.0),
                   (1.0, 0.0, 0.0)),

         'blue':  ((0.0, 0.0, 1.0),
                   (0.5, 0.1, 0.0),
                   (1.0, 0.0, 0.0))
         }

blue_red1 = LinearSegmentedColormap('BlueRed1', cdict1)
plt.imshow(big,interpolation='nearest',  cmap=blue_red1, aspect='auto')
plt.colorbar()
plt.show()

With the above command I get a colour map which is (Red - Black - Blue), Where red being maximum and blue being minimum. I would like to create a colour map which is (Black - White - Black). Could someone tell me what should be done or any other method ?

Answer 1

For what it's worth, there's also a simpler method.

The full form of LinearSegmentedColormap gives you the ability to have "hard" stops and gradients in the same colormap, so it's necessarily complex. However, there's a convenience constructor for simple cases such as what you describe.

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap

cmap = LinearSegmentedColormap.from_list('mycmap', ['black', 'white', 'black'])

fig, ax = plt.subplots()
im = ax.imshow(np.random.random((10, 10)), cmap=cmap, interpolation='nearest')
fig.colorbar(im)
plt.show()