How to get content of Django ImageField before it is saved?

Question

I'm trying to resize an image while saving an instance of my model.

class Picture(models.Model):
  image_file = models.ImageField(upload_to="pictures")
  thumb_file = models.ImageField(upload_to="pictures", editable=False)
  def save(self, force_insert=False, force_update=False):
    image_object = Image.open(self.image_file.path)
    #[...] nothing yet
    super(Picture, self).save(force_insert, force_update)

The problem is that self.image_file.path does not exist before the model is being saved. It returns a correct path, but the image is not there yet. Since there is no image, I can't open it in PIL for resize.

I want to store the thumbnail in thumb_file (another ImageField), so I need do the processing before saving the model.

Is there a good way to open the file (maybe get the tmp image object in memory) or do I have to save the whole model first, resize and then save again ?

Answer 1

I used this snippet:

import Image

def fit(file_path, max_width=None, max_height=None, save_as=None):
    # Open file
    img = Image.open(file_path)

    # Store original image width and height
    w, h = img.size

    # Replace width and height by the maximum values
    w = int(max_width or w)
    h = int(max_height or h)

    # Proportinally resize
    img.thumbnail((w, h), Image.ANTIALIAS)

    # Save in (optional) 'save_as' or in the original path
    img.save(save_as or file_path)

    return True

And in models:

def save(self, *args, **kwargs):
    super(Picture, self).save(*args, **kwargs)
    if self.image:
        fit(self.image_file.path, settings.MAX_WIDTH, settings.MAX_HEIGHT)