How to create a custom diverging colormap in matplotlib?

Question

I want to create a colormap similar to "RdBu" in matplotlib.

I want to make the colormap in this sequence light blue->dark blue-> black(center)->dark red->light red. Something like this.

So it is similar to "RdBu" but white changes to black & dark colors interchanged with light colors. So it is just inverting the "RdBu" colors. I don't know how to do it.

Yes I tried using it, But I couldn't get the result I wanted. — DataNoob

swatchai swatchai · Accepted Answer · 2020-11-17T16:19:30

I just tried to create a colormap to meet my requirements recently. Here is my attempt to build the colormap you need. I know it is not perfect. But it show you how to get started.

import matplotlib
import matplotlib.cm as cm
from matplotlib.colors import Normalize
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import ListedColormap

# create sample data set
# both will be: 0 - 1
x = np.random.rand(400)
y = np.random.rand(400)
# for realistic use
# set extreme values -900, +900 (approx.)
rval = 900
z = ((x+y)-1)*rval

# set up fig/ax for plotting
fig, ax = plt.subplots(figsize=(5, 5))

# option: set background color
ax.set_facecolor('silver')

# the colormap to create
low2hiColor = None

# create listedColormap
bottom = cm.get_cmap('Blues', 256)
top = cm.get_cmap('Reds_r', 256)
mycolormap = np.vstack((bottom(np.linspace(0.25, 1, 64)),
                        np.array([
                        [0.03137255, 0.08823529, 0.41960784, 1.],
                        [0.02137255, 0.04823529, 0.21960784, 1.],
                        [0.01137255, 0.02823529, 0.11960784, 1.],
                        [0.00037255, 0.00823529, 0.00960784, 1.],
                        #[0.00000255, 0.00000529, 0.00060784, 1.],
                        ])
                       ))
mycolormap = np.vstack((mycolormap,
                        np.array([
                        #[0.00060784, 0.00000529, 0.00000255, 1.],
                        [0.00960784, 0.00823529, 0.00037255, 1.],
                        [0.11960784, 0.02823529, 0.01137255, 1.],
                        [0.21960784, 0.04823529, 0.02137255, 1.],
                        [0.41960784, 0.08823529, 0.03137255, 1.],
                        ])
                       ))
mycolormap = np.vstack((mycolormap,
                        top(np.linspace(0, 0.75, 64)),
                       ))

low2hiColor = ListedColormap(mycolormap, name='low2hiColor')

# colorbar is created separately using pre-determined `cmap`
minz = -900 #min(z)
maxz = 900  #max(z)
norm_low2hiColor = matplotlib.colors.Normalize(minz, maxz)

# plot dataset as filled contour
norm1 = matplotlib.colors.Normalize(minz, maxz)
cntr1 = ax.tricontourf(x, y, z, levels=64, cmap=low2hiColor, norm=norm1)

gridlines = ax.grid(b=True)  # this plot grid

cbar= plt.colorbar( cntr1 ) 
plt.title("Light-Dark Blue Black Dark-Light Red")
plt.show()

The sample plot:

How to create a custom diverging colormap in matplotlib?

1 Answers