Bulk update image sizes in a directory

This script takes a specified directory, looks for images based on their file extensions (.png, .jpg, .jpeg, and more), and resizes them to a user-configurable width while maintaining their aspect ratio. The script then saves them to a target directory, rather than overwriting the original file, so you can confirm everything looks good.


Aside from having Python installed, this script requires the Pillow library, which is a fork of PIL (Python Imaging Library). Example command for installation using Homebrew below.

brew install Pillow


import argparse
from PIL import Image
import os

def resize_images(input_directory, output_directory, new_width):
	Resize images in the specified input directory to a specified new width if they are wider than new_width,
	maintaining the aspect ratio, and save them to the output directory.
	# Create the output directory if it doesn't exist
	if not os.path.exists(output_directory):

	for filename in os.listdir(input_directory):
		if filename.lower().endswith(('.png', '.jpg', '.jpeg', '.gif', '.webp')):
			input_path = os.path.join(input_directory, filename)
			output_path = os.path.join(output_directory, filename)

			with Image.open(input_path) as img:
				# Only resize if the image is wider than the specified width
				if img.width > new_width:
					# Calculate the new height to maintain the aspect ratio
					new_height = int((new_width / img.width) * img.height)
					# Resize the image with high-quality resampling
					img = img.resize((new_width, new_height), Image.Resampling.LANCZOS)
					# Save the resized image
					print(f"Resized and saved: {filename}")
					print(f"Skipped resizing: {filename}")

	print("Processing completed.")

if __name__ == "__main__":
	parser = argparse.ArgumentParser(description="Resize images to a specified width while maintaining aspect ratio, only if they are wider than the specified width.")
	parser.add_argument('input_directory', type=str, help='Directory containing the images.')
	parser.add_argument('output_directory', type=str, help='Directory to save the resized or copied images.')
	parser.add_argument('new_width', type=int, help='New width for the images.')
	args = parser.parse_args()
	resize_images(args.input_directory, args.output_directory, args.new_width)


The command takes three parameters:

  • input_directory: Directory containing the images to resize.
  • output_directory: Directory where resized images will be saved.
  • new_width: New width for the images.
python3 resize_images.py path/to/input/directory path/to/output/directory 800

This script can be easily adjusted to support other image file extensions supported by the Python Imaging Library. Reach out if you have any questions or recommendations for improvements.