How to build colorbars without attached plot in matplotlib?

A colorbar in matplotlib is typically attached to a plot to show the color mapping. However, you can create standalone colorbars without any attached plot using ColorbarBase. This is useful for legends or reference scales.

Creating a Basic Standalone Colorbar

Use ColorbarBase to create a colorbar without an associated plot ?

import matplotlib.pyplot as plt
import matplotlib as mpl

# Set figure size
plt.rcParams["figure.figsize"] = [7.00, 3.50]
plt.rcParams["figure.autolayout"] = True

# Create figure and subplot
fig, ax = plt.subplots()

# Adjust layout to make room for colorbar
fig.subplots_adjust(bottom=0.5)

# Create normalization (data range)
norm = mpl.colors.Normalize(vmin=5, vmax=10)

# Create standalone colorbar
cb = mpl.colorbar.ColorbarBase(ax, cmap=mpl.cm.cool, norm=norm, orientation='horizontal')

# Add label
cb.set_label('Temperature (°C)')

plt.show()

Vertical Colorbar Example

Create a vertical standalone colorbar with custom positioning ?

import matplotlib.pyplot as plt
import matplotlib as mpl

# Create figure
fig = plt.figure(figsize=(6, 8))

# Create axis for colorbar
ax = fig.add_axes([0.3, 0.1, 0.4, 0.8])  # [left, bottom, width, height]

# Define normalization and colormap
norm = mpl.colors.Normalize(vmin=0, vmax=100)
cmap = mpl.cm.viridis

# Create vertical colorbar
cb = mpl.colorbar.ColorbarBase(ax, cmap=cmap, norm=norm, orientation='vertical')

# Customize colorbar
cb.set_label('Intensity (%)', rotation=270, labelpad=15)
cb.set_ticks([0, 25, 50, 75, 100])

plt.show()

Multiple Colorbars

Create multiple standalone colorbars in the same figure ?

import matplotlib.pyplot as plt
import matplotlib as mpl
import numpy as np

fig = plt.figure(figsize=(10, 3))

# First colorbar
ax1 = fig.add_subplot(131)
norm1 = mpl.colors.Normalize(vmin=-1, vmax=1)
cb1 = mpl.colorbar.ColorbarBase(ax1, cmap=mpl.cm.RdBu, norm=norm1)
cb1.set_label('Correlation')

# Second colorbar
ax2 = fig.add_subplot(132)
norm2 = mpl.colors.Normalize(vmin=0, vmax=10)
cb2 = mpl.colorbar.ColorbarBase(ax2, cmap=mpl.cm.plasma, norm=norm2)
cb2.set_label('Energy (eV)')

# Third colorbar with discrete colors
ax3 = fig.add_subplot(133)
colors = ['red', 'orange', 'yellow', 'green', 'blue']
cmap3 = mpl.colors.ListedColormap(colors)
norm3 = mpl.colors.BoundaryNorm(range(len(colors)+1), len(colors))
cb3 = mpl.colorbar.ColorbarBase(ax3, cmap=cmap3, norm=norm3)
cb3.set_label('Categories')

plt.tight_layout()
plt.show()

Key Parameters

Conclusion

Use ColorbarBase to create standalone colorbars without plots. This is perfect for creating legends, reference scales, or when you need colorbars independent of data visualization.