Remove a section of a colormap

Question

I really like the "RdBu_r" colormap, but I want to cutout the white part between the blues and reds. Is there an easy way to do this?

Answer 1

Yes, but in your case, it's probably easier to make a colormap that interpolates between blue and red instead.

For example:

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

cmap = LinearSegmentedColormap.from_list('name', ['red', 'blue'])

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

Note that you could substitute the exact RGB values if you wanted a shade of red that isn't an HTML color name.

However, if you did want to "cut out the middle" of another colormap, you'd evaluate it on a range that didn't include the middle and create a new colormap:

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

# Remove the middle 40% of the RdBu_r colormap
interval = np.hstack([np.linspace(0, 0.3), np.linspace(0.7, 1)])
colors = plt.cm.RdBu_r(interval)
cmap = LinearSegmentedColormap.from_list('name', colors)

# Plot a comparison of the two colormaps
fig, axes = plt.subplots(ncols=2)
data = np.random.random((10, 10))

im = axes[0].imshow(data, cmap=plt.cm.RdBu_r, vmin=0, vmax=1)
fig.colorbar(im, ax=axes[0], orientation='horizontal', ticks=[0, 0.5, 1])
axes[0].set(title='Original Colormap')

im = axes[1].imshow(data, cmap=cmap, vmin=0, vmax=1)
fig.colorbar(im, ax=axes[1], orientation='horizontal', ticks=[0, 0.5, 1])
axes[1].set(title='New Colormap')

plt.show()