[SOLVED] Defining the midpoint of a colormap in matplotlib

Defining the midpoint of a colormap in matplotlib

I want to set the middle point of a colormap, i.e., my data goes from -5 to 10 and I want zero to be the middle point. I think the way to do it is by subclassing normalize and using the norm, but I didn't find any example and it is not clear to me, what exactly have I to implement?

Solution

With matplotlib version 3.4 or later, the perhaps simplest solution is to use the new CenteredNorm.

Example using CenteredNorm and one of the diverging colormaps:

import matplotlib.pyplot as plt
import matplotlib as mpl

plt.pcolormesh(data_to_plot, norm=mpl.colors.CenteredNorm(), cmap='coolwarm')

Being simple, CenteredNorm is symmetrical, so that if the data goes from -5 to 10, the colormap will be stretched from -10 to 10. If you want a different mapping on either side of the center, so that the colormap ranges from -5 to 10, use the TwoSlopeNorm as described in @macKaiver's answer.