Creating Thumbnails in Python Using Pillow (PIL)

7

The Pillow library (formerly known as PIL – Python Imaging Library) is a powerful tool for image processing in Python.

One of its useful features is the ability to create thumbnails, which helps in reducing image size while maintaining aspect ratio.

This tutorial covers:
Installing Pillow
Loading and displaying images
Creating thumbnails while preserving aspect ratio
Customizing thumbnail size and quality
Batch processing multiple images

By the end of this guide, you’ll be able to efficiently generate thumbnails using Python.

Installing Pillow

To work with images in Python, install Pillow using pip:

pip install pillow

Once installed, you can verify the installation by importing the module:

from PIL import Image

Loading and Displaying an Image

Before creating a thumbnail, let's learn how to load and display an image using Pillow.

Example: Open and Display an Image

from PIL import Image

# Open an image file
img = Image.open("example.jpg")

# Show the image
img.show()

This code opens an image file named example.jpg and displays it using the default image viewer.

Creating a Simple Thumbnail

To create a thumbnail, we use the thumbnail() method, which resizes the image while maintaining its aspect ratio.

Example: Generate a Thumbnail

from PIL import Image

# Open an image file
img = Image.open("example.jpg")

# Define thumbnail size (width, height)
thumbnail_size = (200, 200)

# Create thumbnail (maintains aspect ratio)
img.thumbnail(thumbnail_size)

# Save the thumbnail
img.save("example_thumbnail.jpg")

# Show the thumbnail
img.show()

How it Works

• thumbnail((200, 200)) resizes the image so that neither width nor height exceeds 200px.
• The aspect ratio is preserved, so the thumbnail might not be exactly 200×200 but fits within that size.
• The thumbnail is saved as “example_thumbnail.jpg”.

Best for: Generating responsive images for web applications.

Customizing Thumbnail Quality

By default, Pillow compresses images while saving. You can improve image quality by specifying the JPEG quality.

Example: Saving Thumbnail with Higher Quality

img.save("example_thumbnail.jpg", quality=95, optimize=True)

Options Explained

• quality=95: Controls compression (default is 75, range 1-100).
• optimize=True: Reduces file size without losing much quality.

Use this when saving thumbnails for high-resolution displays.

Cropping Thumbnails to Exact Size

If you want an exact square thumbnail (e.g., 200x200px), you need to crop the image instead of using thumbnail().

Example: Creating a Fixed-Size Square Thumbnail

from PIL import Image

# Open image
img = Image.open("example.jpg")

# Define target size
thumb_size = (200, 200)

# Get original width and height
width, height = img.size

# Calculate cropping box for a centered crop
left = (width - min(width, height)) / 2
top = (height - min(width, height)) / 2
right = (width + min(width, height)) / 2
bottom = (height + min(width, height)) / 2

# Crop to a square
img_cropped = img.crop((left, top, right, bottom))

# Resize to target size
img_cropped = img_cropped.resize(thumb_size)

# Save the square thumbnail
img_cropped.save("example_square_thumbnail.jpg")

# Show the final image
img_cropped.show()

How it Works

• Crops the centered portion of the image to make it square.
• Resizes the cropped image to exact dimensions (200x200px).

Useful for profile pictures, product thumbnails, or social media images.

Converting to Different Formats

You may need to save thumbnails in different formats like PNG, JPEG, or WEBP.

Example: Save as PNG or WEBP

img.save("example_thumbnail.png", format="PNG")
img.save("example_thumbnail.webp", format="WEBP", quality=90)

WEBP format is useful for websites as it provides smaller file sizes without much loss in quality.

Batch Processing Multiple Images

If you have multiple images in a folder, you can automate thumbnail generation.

Example: Creating Thumbnails for All Images in a Folder

import os
from PIL import Image

# Input and output directories
input_folder = "images/"
output_folder = "thumbnails/"

# Thumbnail size
thumbnail_size = (200, 200)

# Ensure output folder exists
os.makedirs(output_folder, exist_ok=True)

# Process all images in the input folder
for filename in os.listdir(input_folder):
    if filename.endswith((".jpg", ".jpeg", ".png", ".webp")):
        img_path = os.path.join(input_folder, filename)
        img = Image.open(img_path)

        # Create and save thumbnail
        img.thumbnail(thumbnail_size)
        img.save(os.path.join(output_folder, filename))

        print(f"Thumbnail saved: {filename}")

print("Batch processing complete!")

How it Works

• Loops through all .jpg, .jpeg, .png, .webp files in the folder.
• Generates thumbnails and saves them in the thumbnails/ directory.

Perfect for large-scale thumbnail processing!

Creating Watermarked Thumbnails

You can add a watermark to a thumbnail to protect your images.

Example: Adding a Watermark

from PIL import Image, ImageDraw, ImageFont

# Open image
img = Image.open("example.jpg")

# Create thumbnail
img.thumbnail((300, 300))

# Load font (use a TTF font)
font = ImageFont.truetype("arial.ttf", 20)

# Create draw object
draw = ImageDraw.Draw(img)

# Position for watermark
text = "Sample"
text_width, text_height = draw.textsize(text, font=font)
position = (img.width - text_width - 10, img.height - text_height - 10)

# Apply watermark
draw.text(position, text, font=font, fill=(255, 255, 255, 128))

# Save image
img.save("example_watermarked_thumbnail.jpg")

# Show image
img.show()

Great for branding and protecting content!

Summary

Feature	Method
Basic Thumbnail	thumbnail((width, height))
Higher Quality	save(quality=95, optimize=True)
Exact Size Crop	crop((left, top, right, bottom))
Different Formats	save(format=”PNG”)
Batch Processing	os.listdir() & thumbnail()
Watermarking	ImageDraw.text()

Conclusion

Using Pillow (PIL), we can resize, crop, and process images for thumbnails.
The thumbnail() method is efficient and maintains aspect ratio.
Automate thumbnail generation using batch processing.
Save in different formats (JPEG, PNG, WEBP) for flexibility.
Add watermarks for branding.

Now you can create thumbnails efficiently in Python! Let me know if you need any modifications or advanced techniques.