Python – Custom continuous color map in matplotlib

colormapmatplotlibpython

I have read some questions on this subject but I have been unable to find a specific answer to my question.

Let consider the image below:

Color map example

My goal is just to change the limit colors of the map, e.g. in this case the color map goes from dark red to dark blue, let's say I would like it to go from dark green to dark blue. Specifically, I would it to go from colors #244162 to #DCE6F1 (tonalities of blue) in the same continuous way as in the example above.

How is it possible to do this?

[EDIT]

I have tried the following code:

import matplotlib.pyplot as plt
import matplotlib.colors as clr

some_matrix = ...
cmap = clr.LinearSegmentedColormap('custom blue', ['#244162','#DCE6F1'], N=256)
plt.matshow(some_matrix, cmap=cmap)

But I get the error message TypeError: list indices must be integers, not unicode.

Best Answer

LinearSegmentedColormap doesn't take a list of colours, it takes the following argument:

a dictionary with a red, green and blue entries. Each entry should be a list of x, y0, y1 tuples, forming rows in a table. Entries for alpha are optional.

So, you either need to define a dictionary as above, or in your case, I think you just want to use the LinearSegmentedColormap.from_list() method:

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

some_matrix = np.random.rand(10,10)

cmap = clr.LinearSegmentedColormap.from_list('custom blue', ['#244162','#DCE6F1'], N=256)

plt.matshow(some_matrix, cmap=cmap)

plt.show()

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