How to Resize Images with PIL While Maintaining Aspect Ratio?

Resizing Images with PIL While Preserving Aspect Ratio

When creating thumbnails, it can be crucial to maintain the original aspect ratio of images. In this article, we'll explore how to achieve this using the Python Imaging Library (PIL).

Approach:

1. Define Maximum Size: Determine the desired maximum width and height for your thumbnails.
2. Compute Resize Ratio: Calculate the minimum scaling ratio by finding the smaller of the ratios maxwidth/width and maxheight/height.
3. Calculate New Size: Multiply the original size by the computed ratio to obtain the proper size for the thumbnail.

Alternative Method using PIL Library:

PIL provides the Image.thumbnail() method specifically designed for this purpose. It takes the maximum size as an argument and automatically adjusts the image size while maintaining the aspect ratio.

Here's an example from the PIL documentation:

import os, sys
import Image

size = 128, 128

for infile in sys.argv[1:]:
    outfile = os.path.splitext(infile)[0] + ".thumbnail"
    if infile != outfile:
        try:
            im = Image.open(infile)
            im.thumbnail(size, Image.Resampling.LANCZOS)
            im.save(outfile, "JPEG")
        except IOError:
            print "cannot create thumbnail for '%s'" % infile

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