Multiple images in subplot grid in Matplotlib

Introduction

We use multiple images in a subplot grid to compare pictures side by side easily. It helps us see differences or patterns quickly.

Comparing photos from different cameras or settings.

Showing steps of an image processing task.

Displaying different views of the same object.

Presenting multiple charts or heatmaps together.

Visualizing results from different experiments.

Syntax

Matplotlib

import matplotlib.pyplot as plt

fig, axes = plt.subplots(nrows, ncols)

for i, ax in enumerate(axes.flat):
    ax.imshow(image_list[i])
    ax.axis('off')

plt.show()

plt.subplots(nrows, ncols) creates a grid of plots.

Use axes.flat to loop through all subplot axes easily.

Examples

Two images side by side in one row.

Matplotlib

fig, axes = plt.subplots(1, 2)
axes[0].imshow(img1)
axes[1].imshow(img2)
plt.show()

Four images in a 2x2 grid with axes turned off.

Matplotlib

fig, axes = plt.subplots(2, 2)
for i, ax in enumerate(axes.flat):
    ax.imshow(images[i])
    ax.axis('off')
plt.show()

Sample Program

This code creates 4 colored square images and shows them in a 2x2 grid with titles and no axes.

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

# Create 4 simple images with different colors
images = []
colors = [(1, 0, 0), (0, 1, 0), (0, 0, 1), (1, 1, 0)]  # Red, Green, Blue, Yellow
for color in colors:
    img = np.ones((10, 10, 3)) * color
    images.append(img)

fig, axes = plt.subplots(2, 2, figsize=(6, 6))
for i, ax in enumerate(axes.flat):
    ax.imshow(images[i])
    ax.axis('off')
    ax.set_title(f'Image {i+1}')

plt.tight_layout()
plt.show()

Important Notes

Use ax.axis('off') to hide axis ticks and labels for cleaner image display.

Adjust figsize to control the overall size of the subplot grid.

Use plt.tight_layout() to prevent overlapping titles or images.

Summary

Multiple images can be shown in a grid using plt.subplots().

Loop through axes with axes.flat to place images easily.

Turn off axes and add titles for better presentation.

Practice

1. What is the main purpose of using plt.subplots when displaying multiple images in a grid?

easy

A. To change the color of images

B. To load images from files automatically

C. To create a grid of axes where each image can be shown separately

D. To save images to disk

Solution

1. Step 1: Understand the role of plt.subplots

   plt.subplots creates a figure and a grid of axes (subplots) to place multiple plots or images.

2. Step 2: Connect to displaying images

   Each axis in the grid can show one image, so it helps organize multiple images neatly.

3. Final Answer:

   To create a grid of axes where each image can be shown separately -> Option C

4. Quick Check:

   plt.subplots = grid for images [OK]

Hint: Remember: plt.subplots makes the grid for multiple images [OK]

Common Mistakes:

• Thinking plt.subplots loads or saves images
• Confusing plt.subplots with image display functions
• Assuming plt.subplots changes image colors

2. Which of the following is the correct way to loop through all axes in a subplot grid to plot images?

easy

A. for ax in axes.flat:

B. for ax in axes.grid():

C. for ax in axes.loop():

D. for ax in axes.images():

Solution

1. Step 1: Identify the axes object type

   When plt.subplots creates multiple axes, they are stored in an array or matrix.

2. Step 2: Use axes.flat to flatten the array for looping

   axes.flat lets you loop over all axes in a simple 1D way.

3. Final Answer:

   for ax in axes.flat: -> Option A

4. Quick Check:

   axes.flat loops all axes [OK]

Hint: Use axes.flat to loop all subplot axes easily [OK]

Common Mistakes:

• Using non-existent methods like axes.grid()
• Trying to loop axes directly without flattening
• Confusing axes with image objects

3. What will be the output of this code snippet?

import matplotlib.pyplot as plt
import numpy as np
images = [np.random.rand(5,5) for _ in range(4)]
fig, axes = plt.subplots(2, 2)
for ax, img in zip(axes.flat, images):
    ax.imshow(img, cmap='gray')
    ax.axis('off')
plt.show()

medium

A. A single image shown in one plot

B. A 2x2 grid showing 4 random grayscale images without axes

C. An error because axes.flat is not iterable

D. A 2x2 grid with empty plots and no images

Solution

1. Step 1: Understand the code flow

   Four random 5x5 images are created and stored in a list. A 2x2 subplot grid is created.

2. Step 2: Loop through axes and images

   Each axis in the 2x2 grid shows one image with grayscale colormap and axes turned off.

3. Final Answer:

   A 2x2 grid showing 4 random grayscale images without axes -> Option B

4. Quick Check:

   Loop + imshow + axis off = grid of images [OK]

Hint: Loop axes.flat with images to plot all in grid [OK]

Common Mistakes:

• Expecting only one image to show
• Thinking axes.flat is not iterable
• Forgetting to turn axes off

4. Identify the error in this code that tries to display 3 images in a 2x2 grid:

fig, axes = plt.subplots(2, 2)
images = [img1, img2, img3]
for i in range(3):
    axes[i].imshow(images[i])
    axes[i].axis('off')

medium

A. axis('off') is not a valid method

B. images list is empty

C. imshow cannot display images in subplots

D. axes is a 2D array, so axes[i] causes an error

Solution

1. Step 1: Check the type of axes

   plt.subplots(2, 2) returns a 2D array of axes, so axes[i] is invalid indexing.

2. Step 2: Correct way to access axes

   Use axes.flat[i] or flatten axes before indexing to access each subplot.

3. Final Answer:

   axes is a 2D array, so axes[i] causes an error -> Option D

4. Quick Check:

   axes 2D array needs flat for 1D access [OK]

Hint: Use axes.flat to index subplots in 1D [OK]

Common Mistakes:

• Indexing 2D axes array as 1D
• Assuming images list is empty
• Misusing axis('off') method

5. You want to display 6 images in a 2x3 grid with titles on each subplot. Which code snippet correctly does this?

hard

A. fig, axes = plt.subplots(2, 3)
for ax, img, i in zip(axes.flat, images, range(6)):
ax.imshow(img)
ax.set_title(f'Image {i+1}')
ax.axis('off')

B. fig, axes = plt.subplots(3, 2)
for i in range(6):
axes[i].imshow(images[i])
axes[i].title(f'Image {i}')
axes[i].axis('off')

C. fig, axes = plt.subplots(2, 3)
for i in range(6):
axes[i].imshow(images[i])
axes[i].set_title('Image')
axes[i].axis('off')

D. fig, axes = plt.subplots(2, 3)
for ax, img in zip(axes, images):
ax.imshow(img)
ax.set_title('Image')
ax.axis('off')

Solution

1. Step 1: Create correct subplot grid

   plt.subplots(2, 3) creates 2 rows and 3 columns, perfect for 6 images.

2. Step 2: Loop through axes.flat and images with index

   Using axes.flat flattens the 2D axes array for easy looping. Adding index with range(6) helps set titles.

3. Step 3: Set image, title, and turn off axes

   Each axis shows one image, sets a title with number, and hides axis ticks.

4. Final Answer:

   fig, axes = plt.subplots(2, 3) for ax, img, i in zip(axes.flat, images, range(6)): ax.imshow(img) ax.set_title(f'Image {i+1}') ax.axis('off') -> Option A

5. Quick Check:

   axes.flat + set_title + axis off = correct grid [OK]

Hint: Use axes.flat and zip(images, range) for titles [OK]

Common Mistakes:

• Indexing 2D axes as 1D without flat
• Using wrong subplot shape for 6 images
• Calling non-existent title() method