Matplotlib ImageGrid | Data Visualization Tutorial

Introduction

This tutorial will demonstrate how to use Matplotlib's ImageGrid to create a grid of images with shared x and y axes. The tutorial will cover two demos:

Demo 1 shows how to add a colorbar at each axis.
Demo 2 shows how to add a shared colorbar.

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Import necessary libraries

We will use Matplotlib's ImageGrid to create the grid of images. We will also use numpy to generate sample data and cbook to access a sample dataset.

import matplotlib.pyplot as plt
import numpy as np
from matplotlib import cbook
from mpl_toolkits.axes_grid1 import ImageGrid

Define a function to add inner titles to the axes

The function add_inner_title will be used to add titles to the images.

def add_inner_title(ax, title, loc, **kwargs):
    from matplotlib.offsetbox import AnchoredText
    from matplotlib.patheffects import withStroke
    prop = dict(path_effects=[withStroke(foreground='w', linewidth=3)],
                size=plt.rcParams['legend.fontsize'])
    at = AnchoredText(title, loc=loc, prop=prop,
                      pad=0., borderpad=0.5,
                      frameon=False, **kwargs)
    ax.add_artist(at)
    return at

Prepare the sample data

We will use the get_sample_data function from cbook to obtain sample data. We will then prepare the images to be displayed in the grid.

Z = cbook.get_sample_data("axes_grid/bivariate_normal.npy")
extent = (-3, 4, -4, 3)
ZS = [Z[i::3, :] for i in range(3)]
extent = extent[0], extent[1]/3., extent[2], extent[3]

Demo 1 - Colorbar at each axis

We will create a grid of 3 images with a colorbar at each axis using the following code:

grid = ImageGrid(
    fig, 211, nrows_ncols=(1, 3), axes_pad=0.05, label_mode="1", share_all=True,
    cbar_location="top", cbar_mode="each", cbar_size="7%", cbar_pad="1%")
grid[0].set(xticks=[-2, 0], yticks=[-2, 0, 2])

for i, (ax, z) in enumerate(zip(grid, ZS)):
    im = ax.imshow(z, origin="lower", extent=extent)
    cb = ax.cax.colorbar(im)
    ## Changing the colorbar ticks
    if i in [1, 2]:
        cb.set_ticks([-1, 0, 1])

for ax, im_title in zip(grid, ["Image 1", "Image 2", "Image 3"]):
    add_inner_title(ax, im_title, loc='lower left')

We create a grid of 3 images using ImageGrid.
We set the cbar_mode to "each" to add a colorbar at each axis.
We set the share_all parameter to True to share the x and y axes across all the images.
We set the cbar_location parameter to "top" to position the colorbars at the top.
We set the xticks and yticks for the first image.
We loop through each image and add the image to the axis using imshow.
We add a colorbar to each axis using ax.cax.colorbar.
We set the colorbar ticks for the second and third images.
We add a title to each image using add_inner_title.

Demo 2 - Shared colorbar

We will create a grid of 3 images with a shared colorbar using the following code:

grid2 = ImageGrid(
    fig, 212, nrows_ncols=(1, 3), axes_pad=0.05, label_mode="1", share_all=True,
    cbar_location="right", cbar_mode="single", cbar_size="10%", cbar_pad=0.05)
grid2[0].set(xlabel="X", ylabel="Y", xticks=[-2, 0], yticks=[-2, 0, 2])

clim = (np.min(ZS), np.max(ZS))
for ax, z in zip(grid2, ZS):
    im = ax.imshow(z, clim=clim, origin="lower", extent=extent)

## With cbar_mode="single", cax attribute of all axes are identical.
ax.cax.colorbar(im)

for ax, im_title in zip(grid2, ["(a)", "(b)", "(c)"]):
    add_inner_title(ax, im_title, loc='upper left')

We create a grid of 3 images using ImageGrid.
We set the cbar_mode to "single" to add a shared colorbar.
We set the share_all parameter to True to share the x and y axes across all the images.
We set the cbar_location parameter to "right" to position the colorbar at the right.
We set the xticks and yticks for the first image.
We loop through each image and add the image to the axis using imshow.
We set the clim parameter to ensure that all images use the same color scale.
We add a shared colorbar to the axis using ax.cax.colorbar.
We add a title to each image using add_inner_title.

Display the plot

We will use plt.show() to display the plot.

plt.show()

Summary

This tutorial demonstrated how to use Matplotlib's ImageGrid to create a grid of images with shared x and y axes. We covered two demos: Demo 1 showed how to add a colorbar at each axis, and Demo 2 showed how to add a shared colorbar.

Matplotlib ImageGrid Demos for Shared Axes