How do you convert a PIL `Image` to a Django `File`?


Question

I'm trying to convert an UploadedFile to a PIL Image object to thumbnail it, and then convert the PIL Image object that my thumbnail function returns back into a File object. How can I do this?

1
49
3/5/2016 3:43:44 AM

Accepted Answer

The way to do this without having to write back to the filesystem, and then bring the file back into memory via an open call, is to make use of StringIO and Django InMemoryUploadedFile. Here is a quick sample on how you might do this. This assumes that you already have a thumbnailed image named 'thumb':

import StringIO

from django.core.files.uploadedfile import InMemoryUploadedFile

# Create a file-like object to write thumb data (thumb data previously created
# using PIL, and stored in variable 'thumb')
thumb_io = StringIO.StringIO()
thumb.save(thumb_io, format='JPEG')

# Create a new Django file-like object to be used in models as ImageField using
# InMemoryUploadedFile.  If you look at the source in Django, a
# SimpleUploadedFile is essentially instantiated similarly to what is shown here
thumb_file = InMemoryUploadedFile(thumb_io, None, 'foo.jpg', 'image/jpeg',
                                  thumb_io.len, None)

# Once you have a Django file-like object, you may assign it to your ImageField
# and save.
...

Let me know if you need more clarification. I have this working in my project right now, uploading to S3 using django-storages. This took me the better part of a day to properly find the solution here.

95
12/28/2010 8:02:30 AM

I've had to do this in a few steps, imagejpeg() in php requires a similar process. Not to say theres no way to keep things in memory, but this method gives you a file reference to both the original image and thumb (usually a good idea in case you have to go back and change your thumb size).

  1. save the file
  2. open it from filesystem with PIL,
  3. save to a temp directory with PIL,
  4. then open as a Django file for this to work.

Model:

class YourModel(Model):
    img = models.ImageField(upload_to='photos')
    thumb = models.ImageField(upload_to='thumbs')

Usage:

#in upload code
uploaded = request.FILES['photo']
from django.core.files.base import ContentFile
file_content = ContentFile(uploaded.read())
new_file = YourModel() 
#1 - get it into the DB and file system so we know the real path
new_file.img.save(str(new_file.id) + '.jpg', file_content)
new_file.save()

from PIL import Image
import os.path

#2, open it from the location django stuck it
thumb = Image.open(new_file.img.path)
thumb.thumbnail(100, 100)

#make tmp filename based on id of the model
filename = str(new_file.id)

#3. save the thumbnail to a temp dir

temp_image = open(os.path.join('/tmp',filename), 'w')
thumb.save(temp_image, 'JPEG')

#4. read the temp file back into a File
from django.core.files import File
thumb_data = open(os.path.join('/tmp',filename), 'r')
thumb_file = File(thumb_data)

new_file.thumb.save(str(new_file.id) + '.jpg', thumb_file)

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