A django thumbnail support example

imagewiththumbnails.py

class ImageWithThumbnail(models.Model):
     name = models.CharField(max_length = 255)

     image = models.ImageField(upload_to=settings.UPLOAD_ROOT,max_length=500,blank=True,null=True)
     thumbnail = models.ImageField(upload_to=settings.UPLOAD_ROOT,max_length=500,blank=True,null=True)

     def create_thumbnail(self):
         # original code for this method came from
         # http://snipt.net/danfreak/generate-thumbnails-in-django-with-pil/

         # If there is no image associated with this.
         # do not create thumbnail
         if not self.image:
             return

         from PIL import Image
         from cStringIO import StringIO
         from django.core.files.uploadedfile import SimpleUploadedFile
         import os

         # Set our max thumbnail size in a tuple (max width, max height)
         THUMBNAIL_SIZE = (200,200)

         DJANGO_TYPE = self.image.file.content_type

         if DJANGO_TYPE == 'image/jpeg':
             PIL_TYPE = 'jpeg'
             FILE_EXTENSION = 'jpg'
         elif DJANGO_TYPE == 'image/png':
             PIL_TYPE = 'png'
             FILE_EXTENSION = 'png'

         # Open original photo which we want to thumbnail using PIL's Image
         image = Image.open(StringIO(self.image.read()))

         # Convert to RGB if necessary
         # Thanks to Limodou on DjangoSnippets.org
         # http://www.djangosnippets.org/snippets/20/
         #
         # I commented this part since it messes up my png files
         #
         #if image.mode not in ('L', 'RGB'):
         #    image = image.convert('RGB')

         # We use our PIL Image object to create the thumbnail, which already
         # has a thumbnail() convenience method that contrains proportions.
         # Additionally, we use Image.ANTIALIAS to make the image look better.
         # Without antialiasing the image pattern artifacts may result.
         image.thumbnail(THUMBNAIL_SIZE, Image.ANTIALIAS)

         # Save the thumbnail
         temp_handle = StringIO()
         image.save(temp_handle, PIL_TYPE)
         temp_handle.seek(0)

         # Save image to a SimpleUploadedFile which can be saved into
         # ImageField
         suf = SimpleUploadedFile(os.path.split(self.image.name)[-1],
                 temp_handle.read(), content_type=DJANGO_TYPE)
         # Save SimpleUploadedFile into image field
         self.thumbnail.save('%s_thumbnail.%s'%(os.path.splitext(suf.name)[0],FILE_EXTENSION), suf, save=False)

     def save(self):
         # create a thumbnail
         self.create_thumbnail()

         super(ImageWithThumbnail, self).save()

I think you can create multiple SimpleUploadedFile from same StringIO object by calling temp_handle.seek(0) first. For example you can add following code to create_thumbnail method.

     temp_handle.seek(0)

     # Save image to a SimpleUploadedFile which can be saved into
     # ImageField
     suf2 = SimpleUploadedFile(os.path.split(self.image.name)[-1],
             temp_handle.read(), content_type=DJANGO_TYPE)
    self.second_thumbnail.save('%s_thumbnail.%s'%(os.path.splitext(suf2.name)[0],FILE_EXTENSION), suf2, save=False)

If you need thumbnails in different sizes. you should create differend PIL.Image objects for each one.

following blog post shows similar approach
http://codespatter.com/2008/09/13/quick-thumbnails-in-django/