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* NEW: compare images * Fix * add comparison * Implement n_tiles * add unittests for checkerboard * Fancier plots * finalize example * Add versionadded tag * Add note section * unittest for blend * test ValueErrors * float instead of float64 * Fix tests * Update skimage/util/compare.py Co-Authored-By: Mark Harfouche <mark.harfouche@gmail.com> * Update skimage/util/compare.py Co-Authored-By: Mark Harfouche <mark.harfouche@gmail.com> * Update skimage/util/tests/test_compare.py Co-Authored-By: Mark Harfouche <mark.harfouche@gmail.com> * Update skimage/util/tests/test_compare.py Co-Authored-By: Mark Harfouche <mark.harfouche@gmail.com>
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""" | ||
======================= | ||
Visual image comparison | ||
======================= | ||
Image comparison is particularly useful when performing image processing tasks | ||
such as exposure manipulations, filtering, and restauration. | ||
This example shows how to easily compare two images with various approaches. | ||
""" | ||
import matplotlib.pyplot as plt | ||
from matplotlib.gridspec import GridSpec | ||
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from skimage import data, transform, exposure | ||
from skimage.util import compare_images | ||
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img1 = data.coins() | ||
img1_equalized = exposure.equalize_hist(img1) | ||
img2 = transform.rotate(img1, 5) | ||
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comp_equalized = compare_images(img1, img1_equalized, method='checkerboard') | ||
diff_rotated = compare_images(img1, img2, method='diff') | ||
blend_rotated = compare_images(img1, img2, method='blend') | ||
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###################################################################### | ||
# Checkerboard | ||
# ============ | ||
# | ||
# The `checkerboard` method alternates tiles from the first and the second | ||
# images. | ||
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fig = plt.figure(figsize=(8, 9)) | ||
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gs = GridSpec(3, 2) | ||
ax0 = fig.add_subplot(gs[0, 0]) | ||
ax1 = fig.add_subplot(gs[0, 1]) | ||
ax2 = fig.add_subplot(gs[1:, :]) | ||
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ax0.imshow(img1, cmap='gray') | ||
ax0.set_title('Original') | ||
ax1.imshow(img1_equalized, cmap='gray') | ||
ax1.set_title('Equalized') | ||
ax2.imshow(comp_equalized, cmap='gray') | ||
ax2.set_title('Checkerboard comparison') | ||
for a in (ax0, ax1, ax2): | ||
a.axis('off') | ||
plt.tight_layout() | ||
plt.plot() | ||
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###################################################################### | ||
# Diff | ||
# ==== | ||
# | ||
# The `diff` method computes the absolute difference between the two images. | ||
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fig = plt.figure(figsize=(8, 9)) | ||
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gs = GridSpec(3, 2) | ||
ax0 = fig.add_subplot(gs[0, 0]) | ||
ax1 = fig.add_subplot(gs[0, 1]) | ||
ax2 = fig.add_subplot(gs[1:, :]) | ||
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ax0.imshow(img1, cmap='gray') | ||
ax0.set_title('Original') | ||
ax1.imshow(img1_equalized, cmap='gray') | ||
ax1.set_title('Rotated') | ||
ax2.imshow(diff_rotated, cmap='gray') | ||
ax2.set_title('Diff comparison') | ||
for a in (ax0, ax1, ax2): | ||
a.axis('off') | ||
plt.tight_layout() | ||
plt.plot() | ||
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###################################################################### | ||
# Blend | ||
# ===== | ||
# | ||
# `blend` is the result of the average of the two images. | ||
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fig = plt.figure(figsize=(8, 9)) | ||
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gs = GridSpec(3, 2) | ||
ax0 = fig.add_subplot(gs[0, 0]) | ||
ax1 = fig.add_subplot(gs[0, 1]) | ||
ax2 = fig.add_subplot(gs[1:, :]) | ||
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ax0.imshow(img1, cmap='gray') | ||
ax0.set_title('Original') | ||
ax1.imshow(img1_equalized, cmap='gray') | ||
ax1.set_title('Rotated') | ||
ax2.imshow(blend_rotated, cmap='gray') | ||
ax2.set_title('Blend comparison') | ||
for a in (ax0, ax1, ax2): | ||
a.axis('off') | ||
plt.tight_layout() | ||
plt.plot() |
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import numpy as np | ||
from ..util import img_as_float | ||
from itertools import product | ||
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def compare_images(image1, image2, method='diff', *, n_tiles=(8, 8)): | ||
""" | ||
Return an image showing the differences between two images. | ||
.. versionadded:: 0.16 | ||
Parameters | ||
---------- | ||
image1, image2 : 2-D array | ||
Images to process, must be of the same shape. | ||
method : string, optional | ||
Method used for the comparison. | ||
Valid values are {'diff', 'blend', 'checkerboard'}. | ||
Details are provided in the note section. | ||
n_tiles : tuple, optional | ||
Used only for the `checkerboard` method. Specifies the number | ||
of tiles (row, column) to divide the image. | ||
Returns | ||
------- | ||
comparison : 2-D array | ||
Image showing the differences. | ||
Notes | ||
----- | ||
`diff` computes the absolute difference between the two images. | ||
`bend` computes the mean value. | ||
`checkerboard` makes tiles of dimension `n_tiles` that display | ||
alternatively the first and the second image. | ||
""" | ||
if image1.shape != image2.shape: | ||
raise ValueError('Images must have the same shape.') | ||
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img1 = img_as_float(image1) | ||
img2 = img_as_float(image2) | ||
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if method == 'diff': | ||
comparison = np.abs(img2 - img1) | ||
elif method == 'blend': | ||
comparison = 0.5 * (img2 + img1) | ||
elif method == 'checkerboard': | ||
shapex, shapey = img1.shape | ||
mask = np.full((shapex, shapey), False) | ||
stepx = int(shapex / n_tiles[0]) | ||
stepy = int(shapey / n_tiles[1]) | ||
for i, j in product(range(n_tiles[0]), range(n_tiles[1])): | ||
if (i + j) % 2 == 0: | ||
mask[i * stepx:(i + 1)*stepx, j * stepy:(j + 1) * stepy] = True | ||
comparison = np.zeros_like(img1) | ||
comparison[mask] = img1[mask] | ||
comparison[~mask] = img2[~mask] | ||
else: | ||
raise ValueError('Wrong value for `method`. ' | ||
'Must be either "diff", "blend" or "checkerboard".') | ||
return comparison |
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import numpy as np | ||
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from skimage._shared.testing import assert_array_equal | ||
from skimage._shared import testing | ||
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from skimage.util.compare import compare_images | ||
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def test_compate_images_ValueError_shape(): | ||
img1 = np.zeros((10, 10), dtype=np.uint8) | ||
img2 = np.zeros((10, 1), dtype=np.uint8) | ||
with testing.raises(ValueError): | ||
compare_images(img1, img2) | ||
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def test_compare_images_diff(): | ||
img1 = np.zeros((10, 10), dtype=np.uint8) | ||
img1[3:8, 3:8] = 255 | ||
img2 = np.zeros_like(img1) | ||
img2[3:8, 0:8] = 255 | ||
expected_result = np.zeros_like(img1, dtype=np.float64) | ||
expected_result[3:8, 0:3] = 1 | ||
result = compare_images(img1, img2, method='diff') | ||
assert_array_equal(result, expected_result) | ||
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def test_compare_images_blend(): | ||
img1 = np.zeros((10, 10), dtype=np.uint8) | ||
img1[3:8, 3:8] = 255 | ||
img2 = np.zeros_like(img1) | ||
img2[3:8, 0:8] = 255 | ||
expected_result = np.zeros_like(img1, dtype=np.float64) | ||
expected_result[3:8, 3:8] = 1 | ||
expected_result[3:8, 0:3] = 0.5 | ||
result = compare_images(img1, img2, method='blend') | ||
assert_array_equal(result, expected_result) | ||
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def test_compare_images_checkerboard_default(): | ||
img1 = np.zeros((2**4, 2**4), dtype=np.uint8) | ||
img2 = np.full(img1.shape, fill_value=255, dtype=np.uint8) | ||
res = compare_images(img1, img2, method='checkerboard') | ||
exp_row1 = np.array([0., 0., 1., 1., 0., 0., 1., 1., 0., 0., 1., 1., 0., 0., 1., 1.]) | ||
exp_row2 = np.array([1., 1., 0., 0., 1., 1., 0., 0., 1., 1., 0., 0., 1., 1., 0., 0.]) | ||
for i in (0, 1, 4, 5, 8, 9, 12, 13): | ||
assert_array_equal(res[i, :], exp_row1) | ||
for i in (2, 3, 6, 7, 10, 11, 14, 15): | ||
assert_array_equal(res[i, :], exp_row2) | ||
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def test_compare_images_checkerboard_tuple(): | ||
img1 = np.zeros((2**4, 2**4), dtype=np.uint8) | ||
img2 = np.full(img1.shape, fill_value=255, dtype=np.uint8) | ||
res = compare_images(img1, img2, method='checkerboard', n_tiles=(4, 8)) | ||
exp_row1 = np.array( | ||
[0., 0., 1., 1., 0., 0., 1., 1., 0., 0., 1., 1., 0., 0., 1., 1.] | ||
) | ||
exp_row2 = np.array( | ||
[1., 1., 0., 0., 1., 1., 0., 0., 1., 1., 0., 0., 1., 1., 0., 0.] | ||
) | ||
for i in (0, 1, 2, 3, 8, 9, 10, 11): | ||
assert_array_equal(res[i, :], exp_row1) | ||
for i in (4, 5, 6, 7, 12, 13, 14, 15): | ||
assert_array_equal(res[i, :], exp_row2) |