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.

Answer 1

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.ANTIALIAS)             im.save(outfile, "JPEG")         except IOError:             print "cannot create thumbnail for '%s'" % infile 

Answer 2

This script will resize an image (somepic.jpg) using PIL (Python Imaging Library) to a width of 300 pixels and a height proportional to the new width. It does this by determining what percentage 300 pixels is of the original width (img.size[0]) and then multiplying the original height (img.size[1]) by that percentage. Change "basewidth" to any other number to change the default width of your images.

from PIL import Image  basewidth = 300 img = Image.open('somepic.jpg') wpercent = (basewidth/float(img.size[0])) hsize = int((float(img.size[1])*float(wpercent))) img = img.resize((basewidth,hsize), Image.ANTIALIAS) img.save('somepic.jpg')