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This article introduces django in saving images while compressing image sample code how to write, the content is very detailed, interested friends can refer to, I hope to help you.

Assuming we have a very simple Post model, it will be an image and its description,

from django.db import modelsclass Post(models.Model): text = models.TextField() image = models.ImageField(upload_to='images/')

But we want to optimize the image size, which will be indicated by the image field of our Post. There are good reasons for this-it helps load websites/apps faster and reduces our server storage. Before using Django, let's first give you a brief overview of image compression using Pillow.

Compress images with Pillow

Pillow is an excellent Python package for image-related operations. The Image class comes with methods for image io and manipulation. Image.open reads an image from a file path or file object. The save method of the Image class uses quality as an optional parameter for saving images in jpg format, ranging from 1 to 95, the default value for this parameter is 75, and setting quality greater than 95 causes the image to be larger in size than it is.

from PIL import Imageim = Image.open('/some/path/to/image')im.save('/desired/path/new_image_name.jpg', quality=70)im.close()

Using the quality parameter is not the only way to reduce size. For example, you can combine this with resizing the image to get a smaller image size.

Using Django signals

Signals allow certain senders to inform a group of receivers that certain measures have been taken.

Django comes with a number of built-in signals, and for now, we are interested in the django.db.models.signals.pre_save signal, which will be sent before calling the save () method of the model. To connect handlers to signals, there is the Signal.connect method. To attach a signal to a specific sender (in our case, the model), we must provide the sender parameter to the Signal.connect method, for example, attaching the pre_save signal to our Post model (defined above), as follows:

pre_save.connect(our_handler, sender=Post)

Django also provides receiver decorators for connecting signals, which makes the code more idiomatic. Therefore, in addition to defining our_handler and making connections, we can also modify our_handler definition to

from django.dispatch import receiver...@ receiver(pre_save, sender=Post)def my_handler(sender, **kwargs): ...

Now, let's finish processing the program to compress the image. The pre_save signal also sends instance parameters to the handler function corresponding to the actual instance to be saved. This is especially useful when we want to check if fields have been updated, because we don't want to compress images repeatedly. So we can set the handler function to

from django.db.models.signals import pre_savefrom django.dispatch import receiver@receiver(pre_save, sender=Post)def handle_image_compression(sender, instance, **kwargs): try: post_obj = Post.objects.get(pk=instance.pk) except Post.DoesNotExist: # the object does not exists, so compress the image instance.image = compress_image(instance.image) else: # the object exists, so check if the image field is updated if post_obj.image != instance.image: instance.image = compress_image(instance.image)

Now, our final task is to write the compress_image function, which takes an ImageField and returns an ImageField. PIL's Image.open () method can only be used with file paths or file objects. It's an interesting fact that it's a superclass of ImageField, which mirrors python's File API, so we can use it just like we would an actual file. The problem with Image.open has been solved, but what about Image.save? Image.save turns out to be able to write images to BytesIO objects. Therefore, our ability to compress images becomes

from PIL import Imagefrom io import BytesIOfrom django.core.files import Filedef compress_image(image): im = Image.open(image) out = BytesIO() im.save(out, 'JPEG', quality=70) compressed = File(out, name=image.name) im.close() return compressed

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