Django - Create thumbnail on model save. Creates a thumbnail when saving a model by cropping it to square and resizing to 280x280. The thumbnail is not created if the original image is smaller than 280x280, doesn't exist, or if a thumbnail already exists.

gistfile1.py

from cStringIO import StringIO
from django.core.files.base import ContentFile
from django.db import models
from PIL import Image
 
class SomeModel(models.Model):
    image = models.ImageField(upload_to='images', blank=True)
    thumbnail = models.ImageField(upload_to='thumbnails', blank=True)
 
    def create_thumbnail(self):
        # Don't do anything if there is no image to thumbnail.
        # Also, don't overwrite an existing thumbnail
        # (prevents a new thumbnail from being created every save).
        if not self.image or self.thumbnail:
            return
 
        image = Image.open(self.image.file)
 
        # If the image is smaller than 280 x 280,
        # don't bother creating a thumbnail.
        width, height = image.size
        if width < 280 or height < 280:
            return
 
        # Crop as little as possible to square, keeping the center.
        if width > height:
            delta = width - height
            left = int(delta / 2)
            upper = 0
            right = height + left
            lower = height
        else:
            delta = height - width
            left = 0
            upper = int(delta / 2)
            right = width
            lower = width + upper
        image = image.crop((left, upper, right, lower))
 
        # Create the thumbnail as a 280 x 280 square.
        image.thumbnail((280, 280), Image.ANTIALIAS)
 
        # Save the thumbnail in the FileField.
        # Using Image.save(content, 'jpeg') seems to work for pngs too.
        buf = StringIO()
        image.save(buf, 'jpeg', quality=95)
        cf = ContentFile(buf.getvalue())
        self.thumbnail.save(name=self.image.name, content=cf, save=False)
 
    def save(self):
        self.create_thumbnail()
        super(SomeModel, self).save()