Django snippets: Filter to resize a ImageField on demand

Filter to resize a ImageField on demand

import os
import Image
from django.template import Library


register = Library()


def thumbnail(file, size='200x200'):
    # defining the size
    x, y = [int(x) for x in size.split('x')]
    # defining the filename and the miniature filename
    basename, format = file.rsplit('.', 1)
    miniature = basename + '_' + size + '.' +  format
    miniature_filename = os.path.join(settings.MEDIA_ROOT, miniature)
    miniature_url = os.path.join(settings.MEDIA_URL, miniature)
    # if the image wasn't already resized, resize it
    if not os.path.exists(miniature_filename):
        print '>>> debug: resizing the image to the format %s!' % size
        filename = os.path.join(settings.MEDIA_ROOT, file)
        image = Image.open(filename)
        image.thumbnail([x, y]) # generate a 200x200 thumbnail
        image.save(miniature_filename, image.format)
    return miniature_url


register.filter(thumbnail)

A filter to resize a ImageField on demand, a use case could be:

<img src="object.get_image_url" alt="original image"> <img src="object.image|thumbnail" alt="image resized to default 200x200 format"> <img src="object.image|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.

There is a TODO: the filter isn't checking if the original filename is newer than the cached resized image, it should check it and resize the image again in this case.

Author:: michelts
Posted:: April 19, 2007
Language:: Python
Tags:: filter imagefield models resize thumbnail
Score:: 12 (after 12 ratings)

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Archatas (on April 19, 2007):

Shouldn't there be something like

thumbnail = register.filter(thumbnail)

at the end of the snippet?

alexkoval (on July 9, 2007):

the first thing which I've noticed is that thumbnail was not regenerated when I replaced main image. I suggest fix so thumbnail is removed (and then regenerated) when its outdated. I also had to move up filename= line.

miniature = basename + '_' + size + '.' +  format
filename = os.path.join(settings.MEDIA_ROOT, file)
miniature_filename = os.path.join(settings.MEDIA_ROOT, miniature)
miniature_url = os.path.join(settings.MEDIA_URL, miniature)
if os.path.exists(miniature_filename) and \
       os.path.getmtime(filename)>os.path.getmtime(miniature_filename):
    os.unlink(miniature_filename)

alexkoval (on July 9, 2007):

also... Thumbnails are bad quality, I recommend adding anti aliasing when resizing:

    image.thumbnail([x, y],Image.ANTIALIAS) # generate a 200x200 thumbnail

javinievas (on October 22, 2007):

For people like me using filestorage (http://code.djangoproject.com/ticket/5361), this is the working modified code.

def thumbnail(file, size='100x150'):
    # defining the size
    x, y = [int(x) for x in size.split('x')]
    # defining the filename and the miniature filename
    basename, format = file.rsplit('.', 1)
    miniature = basename + '_' + size + '.' +  format
    miniature_nomedia = miniature[len(settings.MEDIA_URL):]
    file_nomedia = file[len(settings.MEDIA_URL):]
    filename = os.path.join(settings.MEDIA_ROOT, file_nomedia)
    miniature_filename = os.path.join(settings.MEDIA_ROOT, miniature_nomedia)
    miniature_url = miniature
    if os.path.exists(miniature_filename) and os.path.getmtime(filename)>os.path.getmtime(miniature_filename):
        os.unlink(miniature_filename)
    # if the image wasn't already resized, resize it
    if not os.path.exists(miniature_filename):
        image = Image.open(filename)
        image.thumbnail([x, y], Image.ANTIALIAS) # generate a 200x200 thumbnail
        image.save(miniature_filename, image.format)
    return miniature_url

Django snippets

Filter to resize a ImageField on demand

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