Search code examples
pythonmatplotlibcolorbarimshow

Log labels on colorbar

I have a logarithmic imshow figure, and when the colorbar is created, its axis labels and ticks are logarithmic, but because of the short range (0-50) of the values, the colorbar looks like this:

enter image description here

and I would like it to instead show as 0, 5, 10, 20, 50 spaced along the axis (logarithmic spacing).

Solution

  • Use the LogFormatter class and set labelOnlyBase to False:

    import matplotlib.pyplot as plt
import numpy as np
import matplotlib.colors
from matplotlib.ticker import LogFormatter 

np.random.seed(2023)  # for reproducible sample data
A = np.random.rand(50,50)*50
plt.imshow(A, norm=matplotlib.colors.LogNorm())
formatter = LogFormatter(10, labelOnlyBase=False) 
cb = plt.colorbar(ticks=[1,5,10,20,50], format=formatter)
plt.show()

    enter image description here