django-storage-thumbnails

Automatically generate image thumbnails whenever a file is saved through a Django storage backend. Works with local filesystem storage and Amazon S3 (via django-storages).

Install

pip install django-storage-thumbnails          # local filesystem
pip install "django-storage-thumbnails[s3]"     # + S3 support

Configure

Add the sizes you want to your Django settings. Sizes accept either a (width, height) tuple or a "WxH" string:

THUMBNAIL_SIZES = {
    "small": (10, 10),
    "med": (20, 20),
}

Then point your model/field (or STORAGES) at a thumbnail-aware storage.

Local filesystem

from thumbnail_storage import ThumbnailFileSystemStorage

storage = ThumbnailFileSystemStorage()
name = storage.save("photos/cat.jpg", my_image_file)
# also writes: thumbnails/small/photos/cat.jpg, thumbnails/med/photos/cat.jpg

Amazon S3

from thumbnail_storage import ThumbnailS3Storage

storage = ThumbnailS3Storage(bucket_name="my-bucket")
storage.save("photos/cat.jpg", my_image_file)

In a model

from django.db import models
from thumbnail_storage import ThumbnailFileSystemStorage

class Photo(models.Model):
    image = models.ImageField(
        upload_to="photos/",
        storage=ThumbnailFileSystemStorage(),
    )

Getting thumbnail links

Thumbnails are stored under a dedicated thumbnails/<size>/ prefix so they can never collide with or overwrite a user's uploaded file. Deleting the original also removes its thumbnails.

storage.thumbnail_url("photos/cat.jpg", "small")
# -> "/media/thumbnails/small/photos/cat.jpg"

storage.get_thumbnails("photos/cat.jpg")
# -> {"small": "/media/thumbnails/small/photos/cat.jpg",
#     "med":   "/media/thumbnails/med/photos/cat.jpg"}

Use it with any backend

ThumbnailMixin can be mixed into any Django Storage subclass:

from thumbnail_storage import ThumbnailMixin
from storages.backends.azure_storage import AzureStorage

class ThumbnailAzureStorage(ThumbnailMixin, AzureStorage):
    pass

Async generation with Celery (S3)

For S3, you usually don't want to block the upload request while thumbnails are generated. Use the async storage: it saves the original immediately and hands the thumbnail work to a Celery worker, which re-reads the original from S3 — so only the file name travels over the broker, never the image bytes.

pip install "django-storage-thumbnails[s3,celery]"

Register the storage under a key in STORAGES and pass that key as alias (the worker uses it to rebuild the same backend):

# settings.py
STORAGES = {
    "default": {"BACKEND": "django.core.files.storage.FileSystemStorage"},
    "thumbnails": {
        "BACKEND": "thumbnail_storage.AsyncThumbnailS3Storage",
        "OPTIONS": {"alias": "thumbnails", "bucket_name": "my-bucket"},
    },
}

from django.core.files.storage import storages

storage = storages["thumbnails"]
storage.save("photos/cat.jpg", img)   # returns immediately; thumbnails follow

Make sure your Celery app autodiscovers thumbnail_storage.tasks, and that the worker can reach the same S3 bucket. If Celery isn't installed, generation quietly falls back to running inline.

Fetching while a thumbnail is still being made

Names are deterministic, so thumbnail_url() returns the URL right away — even before the worker finishes. Use it with a fallback to the original so there's no broken image in the brief window before the thumbnail exists:

<img src="{{ small_url }}" onerror="this.onerror=null; this.src='{{ original_url }}'">

Need a guaranteed "ready" signal or to generate sizes only on first view? The get_thumbnail_name and store_thumbnail methods are overridable — subclass to record a status row or to generate lazily, without forking the package.

How it works

On _save, if the saved file's extension is a known image type and THUMBNAIL_SIZES is non-empty, a thumbnail is generated for each size with Pillow (Image.thumbnail, which preserves aspect ratio — so a "10x10" size is a bounding box, not an exact crop) and saved under thumbnails/<key>/<name> in the same backend. Non-images and unreadable files are passed through untouched, and any per-size failure is logged and skipped without affecting the upload or the other sizes. Override thumbnail_prefix to change the namespace, or get_thumbnail_name / store_thumbnail to change naming or write behavior.

Cleanup on delete() removes the thumbnails for the current THUMBNAIL_SIZES / thumbnail_prefix. If you remove a size key or change the prefix later, thumbnails generated under the old config are not tracked and won't be cleaned up automatically — prune them out of band if needed.

Running the tests

pip install -e ".[test]"
pytest