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A colormap is a simple way to map data values ​​to colors. Inverting a colormap means reversing the colormap for each value. Suppose we have a colormap where lower values ​​are mapped to yellow and higher values ​​are mapped to red. By inverting colormap, lower values ​​are now mapped to red and higher values ​​are mapped to yellow. This tutorial explains various ways to invert a colormap in Python Matplotlib.

Colormaps in Python Matplotlib

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(9)
y = [9, 2, 8, 4, 5, 7, 6, 8, 7]

plt.scatter(x, y, c=y, cmap="viridis")
plt.xlabel("X")
plt.ylabel("Y")
plt.title("Scatter Plot with Virdis colormap")
plt.colorbar()
plt.show()

It creates a scatter plot with its y values ​​mapped to viridisthe colormap. This means that points with low y values ​​will appear dark blue, points with high y values ​​will appear yellow, and points in between will appear blue and green.

We can also see a colorbar on the right side of the plot, which shows the color mapping for different values ​​of y.

_rInverse color mapping in Matplotlib Python using

In Matplotlib, we can _rinvert a colormap by adding at the end of the colormap name, for example cmap='viridis_r'will simply invert viridisthe colormap.

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(9)
y = [9, 2, 8, 4, 5, 7, 6, 8, 7]

plt.scatter(x, y, c=y, cmap="viridis_r")
plt.xlabel("X")
plt.ylabel("Y")
plt.title("Scatter Plot with Inverse Virdis colormap")
plt.colorbar()
plt.show()

It creates a scatter plot with the y values ​​mapped to the inverted viridiscolormap, so that the higher value points in the plot get dark blue and the lower value points get yellow.

We can also see that in this example the colorbar on the right has inverted colors.

matplotlib. colors.Colormap.reversed()Invert Colormap in Matplotlib Python

Another way to invert a Colormap in Python is to use matplotlib.color.Colormap.reversed()the method to create an inverted Colormap.

import numpy as np
import matplotlib.pyplot as plt
from matplotlib import cm

x = np.arange(9)
y = [9, 2, 8, 4, 5, 7, 6, 8, 7]

initial_cmap = cm.get_cmap("viridis")
reversed_cmap = initial_cmap.reversed()

plt.scatter(x, y, c=y, cmap=reversed_cmap)
plt.xlabel("X")
plt.ylabel("Y")
plt.title("Scatter Plot with Inverse Virdis colormap")
plt.colorbar()
plt.show()

It also creates a scatter plot with the y values ​​mapped to the inverted viridiscolormap. reversed()The method inverts the colormap object to which it is applied.

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

x = np.arange(9)
y = [9, 2, 8, 4, 5, 7, 6, 8, 7]

initial_cmap = cm.get_cmap("viridis")
reversed_cmap = ListedColormap(initial_cmap.colors[::-1])

plt.scatter(x, y, c=y, cmap=reversed_cmap)
plt.xlabel("X")
plt.ylabel("Y")
plt.title("Scatter Plot with Inverse Virdis colormap")
plt.colorbar()
plt.show()

It also creates a scatter plot with the y values ​​mapped to the inverted viridiscolormap. Any colormap is just a list of colors. We can cmap. colorsaccess the color list of a colormap using cmap. We then invert the list and finally convert the inverted list back to a colormap using the function matplotlib.colsfrom the package .ListedColormap()