How do I resize an image using PIL and maintain its aspect ratio?

Question

Is there an obvious way to do this that I'm missing? I'm just trying to make thumbnails.

Accepted Answer

Define a maximum size. Then, compute a resize ratio by taking `min(maxwidth/width, maxheight/height)`.

The proper size is `oldsize*ratio`.

There is of course also a library method to do this: the method `Image.thumbnail`. Below is an (edited) 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
```

How do I resize an image using PIL and maintain its aspect ratio?

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