Fighting Rabbits

{{ object.image|make_thumbnail:'100x200' }}

import os
import Image
 
from django.template import Library, Node
from django.template import Variable, resolve_variable
from django.core.urlresolvers import reverse
from django.contrib.contenttypes.models import ContentType
 
register = Library()
 
def make_thumbnail(file, size='200x200'):
    """
    Example:
    <img src="object.get_image_url" alt="original image" />
    <img src="object.image|make_thumbnail" alt="image resized to default 200x200 format" />
    <img src="object.image|make_thumbnail:'200x300'" alt="image resized to 200x300" />
 
    The filter is applied to a image field (not the image url get from
    get_image_url method of the model), supposing the image filename is
    "image.jpg", it checks if there is a file called "image_200x200.jpg" or
    "image_200x300.jpg" on the second case, if the file isn't there, it resizes
    the original image, finally it returns the proper url to the resized image.
    """
 
    if file:
        # defining the size
        x, y = [int(x) for x in size.split('x')]
        # defining the filename and the miniature filename
        basename, format = file.path.rsplit('.', 1)
        baseurl, _format = file.url.rsplit('.', 1)
        miniature_filename = basename + '_' + size + '.' +  format
        miniature_url = baseurl + '_' + size + '.' +  format
 
        # if the image wasn't already resized, resize it
        if not os.path.exists(miniature_filename):
            image = Image.open(file.path)
            pw = image.size[0]
            ph = image.size[1]
            nw = x
            nh = y
            pr = float(pw) / float(ph)
            nr = float(nw) / float(nh)
 
            if image.mode not in ('L', 'RGB'):
                image = image.convert('RGB')
 
            if pw == nw and ph == nh:
                pass
            else:
                if pr > nr:
                    # image aspect is wider than destination ratio
                    tw = int(round(nh * pr))
                    image = image.resize((tw, nh), Image.ANTIALIAS)
                    l = int(round(( tw - nw ) / 2.0))
                    image = image.crop((l, 0, l + nw, nh))
                elif pr < nr:
                    # image aspect is taller than destination ratio
                    th = int(round(nw / pr))
                    image = image.resize((nw, th), Image.ANTIALIAS)
                    t = int(round(( th - nh ) / 2.0))
                    image = image.crop((0, t, nw, t + nh))
                else:
                    # image aspect matches the destination ratio
                    image = image.resize(size, Image.ANTIALIAS)
            image.save(miniature_filename, image.format)
        return miniature_url
 
    return ''
 
register.filter(make_thumbnail)

{% load thumbs_filter %}
{{ object.image|make_thumbnail:'100x200' }}