Usage examples

The following examples showcase the functionality of pyimagetest. This requires some backends to be installed. You can either install them for each example individually or simply install all builtin backends.

General usage

• Requirements: pip install imageio Pillow

ImageTestCase provides two convenience methods to ease unit testing with images:

1. load_image() loads and image from a file with a given backend.

2. assertImagesAlmostEqual() compares two images of possible different backends on equality.

A simple I/O test that compares imageio and Pillow could look like this:

import pyimagetest
from os import path

class ImageTester(pyimagetest.ImageTestCase):
    def test_io(self):
        file = path.join("path", "to", "test", "image")

        imageio_image = self.load_image(file, backend="imageio")
        pil_image = self.load_image(file, backend="PIL")

        self.assertImagesAlmostEqual(imageio_image, pil_image)

Working with a single backend and / or file

• Requirements: pip install imageio

If you mainly work with a single image backend and / or a file, you can ease up your workflow by overwriting default_image_backend() and / or default_image_file(). The return values are then used in load_image() if no backend and / or file is given:

import pyimagetest
from os import path

class ImageTester(pyimagetest.ImageTestCase):
    def default_image_backend(self):
        return "imageio"

    def default_image_file(self):
        return path.join("path", "to", "test", "image")

    def test_io(self):
        file = path.join("path", "to", "test", "image")
        backend = "imageio"

        specific_image = self.load_image(file, backend)
        default_image = self.load_image()

        self.assertImagesAlmostEqual(specific_image, default_image)

Creating a custom backend

• Requirements: pip install imageio

If you want to work with an backend not included in pyimagetest you can create your own by subclassing ImageBackend:

from pyimagetest.backends import ImageBackend
import imageio


class MyImage:
    @staticmethod
    def from_numpy(data):
        ...

    def to_numpy(self):
        ...


class MyBackend(ImageBackend):
    def native_image_type(self):
        return MyImage

    def import_image(self, file):
        return MyImage.from_numpy(imageio.imread(file))

    def export_image(self, image):
        return image.to_numpy()

To able to access MyBackend at runtime you can add it within the constructor of the test case:

import pyimagetest
from os import path


class ImageTester(pyimagetest.ImageTestCase):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.add_image_backend("MyBackend", MyBackend())

    def test_my_backend(self):
        file = path.join("path", "to", "test", "image")

        my_image = self.load_image(file, backend="MyBackend")

Note

If you add a custom backend with the same native_image_type() as a builtin backend, you can remove the builtin one with remove_image_backend(). Otherwise the automatic backend inference of assertImagesAlmostEqual() might not work as intended.

Note

If you create a custom backend based on an open-source Python package, consider contributing it to pyimagetest.