Pillow/Tests/test_imageenhance.py

from PIL import Image, ImageEnhance

from .helper import PillowTestCase, assert_image_equal, hopper


class TestImageEnhance(PillowTestCase):
    def test_sanity(self):

        # FIXME: assert_image
        # Implicit asserts no exception:
        ImageEnhance.Color(hopper()).enhance(0.5)
        ImageEnhance.Contrast(hopper()).enhance(0.5)
        ImageEnhance.Brightness(hopper()).enhance(0.5)
        ImageEnhance.Sharpness(hopper()).enhance(0.5)

    def test_crash(self):

        # crashes on small images
        im = Image.new("RGB", (1, 1))
        ImageEnhance.Sharpness(im).enhance(0.5)

    def _half_transparent_image(self):
        # returns an image, half transparent, half solid
        im = hopper("RGB")

        transparent = Image.new("L", im.size, 0)
        solid = Image.new("L", (im.size[0] // 2, im.size[1]), 255)
        transparent.paste(solid, (0, 0))
        im.putalpha(transparent)

        return im

    def _check_alpha(self, im, original, op, amount):
        self.assertEqual(im.getbands(), original.getbands())
        assert_image_equal(
            im.getchannel("A"),
            original.getchannel("A"),
            "Diff on {}: {}".format(op, amount),
        )

    def test_alpha(self):
        # Issue https://github.com/python-pillow/Pillow/issues/899
        # Is alpha preserved through image enhancement?

        original = self._half_transparent_image()

        for op in ["Color", "Brightness", "Contrast", "Sharpness"]:
            for amount in [0, 0.5, 1.0]:
                self._check_alpha(
                    getattr(ImageEnhance, op)(original).enhance(amount),
                    original,
                    op,
                    amount,
                )