Image field for Django
Project description
Heavily based on django-versatileimagefield, but with a few important differences:
The amount of code is kept at a minimum. django-versatileimagefield has several times as much code (without tests).
Generating images on-demand inside rendering code is made hard on purpose. Instead, images are generated when models are saved and also by running the management command process_imagefields.
django-imagefield does not depend on a fast storage or a cache to be and stay fast, at least as long as the image width and height is saved in the database.
django-imagefield fails early when image data is incomplete or not processable by Pillow for some reason.
Replacing existing uses of django-versatileimagefield requires the following steps:
from imagefield.fields import ImageField as VersatileImageField, PPOIField
Specify the image sizes by either providing ImageField(formats=...) or adding the IMAGEFIELD_FORMATS setting.
Convert template code to access the new properties.
When using django-imagefield with a PPOI, make sure that the PPOI field is also added to ModelAdmin or InlineModelAdmin fieldsets, otherwise you’ll just see the image, but no PPOI picker.
If you used e.g. instance.image.crop.200x200 and instance.image.thumbnail.800x500 before, you should add the following setting:
IMAGEFIELD_FORMATS = {
# image field path, lowercase
'yourapp.yourmodel.image': {
'square': ['default', ('crop', (200, 200))],
'full': ['default', ('thumbnail', (800, 500))],
},
}
After running ./manage.py process_imagefields once you can now use use instance.image.square and instance.image.thumbnail in templates instead. Note that the properties on the image file do by design not check whether thumbs exist.
Image processors
django-imagefield uses an image processing pipeline modelled after Django’s middleware.
The following processors are available out of the box:
autorotate: Autorotates an image by reading the EXIF data.
process_jpeg: Converts non-RGB images to RGB, activates progressive encoding and sets quality to a higher value of 90.
process_gif: Preserves transparency and palette data in resized images.
preserve_icc_profile: As the name says.
thumbnail: Resizes images to fit a bounding box.
crop: Crops an image to the given dimensions, also takes the PPOI (primary point of interest) information into account if provided.
default: The combination of autorotate, process_jpeg, process_gif and preserve_icc_profile. Additional default processors may be added in the future. It is recommended to use default instead of adding the processors one-by-one.
Processors can be specified either using their name alone, or if they take arguments, using a tuple (processor_name, args...).
You can easily register your own processors or even override built-in processors if you want to:
from imagefield.processing import register
# You could also write a class with a __call__ method, but I really
# like the simplicity of functions.
@register
def my_processor(get_image, args):
# args is either a list of arguments to the processor or an
# empty list
def processor(image, context):
# read some information from the image...
# or maybe modify it, but it's mostly recommended to modify
# the image after calling get_image
image, context = get_image(image, context)
# modify the image, and return it...
modified_image = ...
# maybe modify the context...
return modified_image, context
return processor
The processor’s name is taken directly from the registered object.
The context is a types.SimpleNamespace containing the following variables (but feel free to add your own):
ppoi: The primary point of interest as a list of two floats between 0 and 1.
save_kwargs: A dictionary of keyword arguments to pass to PIL.Image.save.
Development
django-imagefield uses both flake8 and isort to check for style violations. It is recommended to add the following git hook as an executable file at .git/hooks/pre-commit:
#!/bin/bash set -ex export PYTHONWARNINGS=ignore tox -e style
The easiest way to build the documentation and run the test suite is using tox:
tox -e docs # Open docs/build/html/index.html tox -e tests
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