74 lines
3.2 KiB
Python
74 lines
3.2 KiB
Python
from pathlib import Path
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import shutil
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import pytest
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from pytest import approx
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from matplotlib.testing.compare import compare_images
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from matplotlib.testing.decorators import _image_directories
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# Tests of the image comparison algorithm.
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@pytest.mark.parametrize(
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'im1, im2, tol, expect_rms',
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[
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# Comparison of an image and the same image with minor differences.
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# This expects the images to compare equal under normal tolerance, and
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# have a small RMS.
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('basn3p02.png', 'basn3p02-minorchange.png', 10, None),
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# Now test with no tolerance.
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('basn3p02.png', 'basn3p02-minorchange.png', 0, 6.50646),
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# Comparison with an image that is shifted by 1px in the X axis.
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('basn3p02.png', 'basn3p02-1px-offset.png', 0, 90.15611),
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# Comparison with an image with half the pixels shifted by 1px in the X
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# axis.
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('basn3p02.png', 'basn3p02-half-1px-offset.png', 0, 63.75),
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# Comparison of an image and the same image scrambled.
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# This expects the images to compare completely different, with a very
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# large RMS.
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# Note: The image has been scrambled in a specific way, by having
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# each color component of each pixel randomly placed somewhere in the
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# image. It contains exactly the same number of pixels of each color
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# value of R, G and B, but in a totally different position.
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# Test with no tolerance to make sure that we pick up even a very small
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# RMS error.
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('basn3p02.png', 'basn3p02-scrambled.png', 0, 172.63582),
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# Comparison of an image and a slightly brighter image.
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# The two images are solid color, with the second image being exactly 1
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# color value brighter.
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# This expects the images to compare equal under normal tolerance, and
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# have an RMS of exactly 1.
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('all127.png', 'all128.png', 0, 1),
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# Now test the reverse comparison.
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('all128.png', 'all127.png', 0, 1),
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])
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def test_image_comparison_expect_rms(im1, im2, tol, expect_rms, tmp_path,
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monkeypatch):
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"""
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Compare two images, expecting a particular RMS error.
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im1 and im2 are filenames relative to the baseline_dir directory.
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tol is the tolerance to pass to compare_images.
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expect_rms is the expected RMS value, or None. If None, the test will
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succeed if compare_images succeeds. Otherwise, the test will succeed if
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compare_images fails and returns an RMS error almost equal to this value.
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"""
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# Change the working directory using monkeypatch to use a temporary
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# test specific directory
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monkeypatch.chdir(tmp_path)
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baseline_dir, result_dir = map(Path, _image_directories(lambda: "dummy"))
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# Copy "test" image to result_dir, so that compare_images writes
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# the diff to result_dir, rather than to the source tree
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result_im2 = result_dir / im1
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shutil.copyfile(baseline_dir / im2, result_im2)
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results = compare_images(
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baseline_dir / im1, result_im2, tol=tol, in_decorator=True)
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if expect_rms is None:
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assert results is None
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else:
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assert results is not None
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assert results['rms'] == approx(expect_rms, abs=1e-4)
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