[FIXED] how to extract a subset of a colormap as a new colormap in matplotlib?

Issue

I would like to use a colormap from matplotlib e.g. CMRmap. But I don't want to use the "black" color at the beginning and the "white" color at the end. I'm interested to plot my data using the in-between colors. I think ppl use it quite often but I was searching over internet and could not manage to find any simple solution. I'll appreciate if someone suggest any solution.

Solution

The staticmethod colors.LinearSegmentedColormap.from_list can be used to create new LinearSegmentedColormaps. Below, I sample the original colormap at 100 points between 0.2 and 0.8:

cmap(np.linspace(0.2, 0.8, 100))

and use these colors to generate a new colormap:

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

def truncate_colormap(cmap, minval=0.0, maxval=1.0, n=100):
    new_cmap = colors.LinearSegmentedColormap.from_list(
        'trunc({n},{a:.2f},{b:.2f})'.format(n=cmap.name, a=minval, b=maxval),
        cmap(np.linspace(minval, maxval, n)))
    return new_cmap

arr = np.linspace(0, 50, 100).reshape((10, 10))
fig, ax = plt.subplots(ncols=2)

cmap = plt.get_cmap('jet')
new_cmap = truncate_colormap(cmap, 0.2, 0.8)
ax[0].imshow(arr, interpolation='nearest', cmap=cmap)
ax[1].imshow(arr, interpolation='nearest', cmap=new_cmap)
plt.show()

The plot on the left shows the image using the original colormap (in this example, jet). The plot on the right shows the same image using new_cmap.

Answered By - unutbu