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Fixed imsave() saving incorrect color map #29203

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Fixed imsave() saving incorrect color map #29203

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07226ab
Fixed issue #29183 such that imsave() handled list-of-list-of-list an…
Nov 28, 2024
e491c52
Removed debugging lines and prints.
Nov 28, 2024
e4bdd84
Added one roundtrip unit test case for imsave() together with imread().
Nov 28, 2024
c16b4b0
Changed functions names and added comment, also ran flake8 linter loc…
Nov 29, 2024
3faf4e2
Removed confusing import mimage.
Dec 6, 2024
0df1f51
Cleaned commit history, and modified code according to reviewer's sug…
gpxxlt Dec 14, 2024
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1 change: 1 addition & 0 deletions lib/matplotlib/axes/_axes.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5869,6 +5869,7 @@ def imshow(self, X, cmap=None, norm=None, *, aspect=None,
`~matplotlib.pyplot.imshow` expects RGB images adopting the straight
(unassociated) alpha representation.
"""

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Suggested change

im = mimage.AxesImage(self, cmap=cmap, norm=norm, colorizer=colorizer,
interpolation=interpolation, origin=origin,
extent=extent, filternorm=filternorm,
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7 changes: 7 additions & 0 deletions lib/matplotlib/image.py
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Expand Up @@ -28,6 +28,7 @@
Affine2D, BboxBase, Bbox, BboxTransform, BboxTransformTo,
IdentityTransform, TransformedBbox)


_log = logging.getLogger(__name__)

# map interpolation strings to module constants
Expand Down Expand Up @@ -1093,6 +1094,7 @@ def set_data(self, x, y, A):
"""
Set the grid for the pixel centers, and the pixel values.


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Parameters
----------
x, y : 1D array-like
Expand Down Expand Up @@ -1582,6 +1584,10 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
_api.check_in_list(('upper', 'lower'), origin=origin)
if origin == "lower":
arr = arr[::-1]

if (isinstance(arr, list)):
arr = np.asarray(arr, dtype=np.uint8)

Comment on lines +1587 to +1590
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Let's move the format coersion above the origin handling. While the reversal ([::-1]) also works for lists, it's more efficient and easier to understand if we ensure that we have the array already there.

Also arr = np.asanyarray(array) should be enough.

  • asanyarray() instead of asarray() Passing through array subclasses should be ok - we currently do that as well.
  • let's not do dtype conversion in this PR - we currently also don't do this for arrays. The user is responsible for passing reasonable types. Any change to that would be a separate topic.

if (isinstance(arr, memoryview) and arr.format == "B"
and arr.ndim == 3 and arr.shape[-1] == 4):
# Such an ``arr`` would also be handled fine by sm.to_rgba below
Expand Down Expand Up @@ -1630,6 +1636,7 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
background = PIL.Image.new("RGB", pil_shape, color)
background.paste(image, image)
image = background

pil_kwargs.setdefault("format", format)
pil_kwargs.setdefault("dpi", (dpi, dpi))
image.save(fname, **pil_kwargs)
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19 changes: 19 additions & 0 deletions lib/matplotlib/tests/test_image.py
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Expand Up @@ -197,6 +197,25 @@ def test_imsave_fspath(fmt):
plt.imsave(Path(os.devnull), np.array([[0, 1]]), format=fmt)


def test_imsave_python_vanilla_list():
# Initializing RGBA data
# Instead of testing numpy array, use python list
input_img = [
[[255, 0, 0, 1], [0, 255, 0, 1], [0, 0, 255, 1]],
[[0, 255, 0, 1], [0, 255, 0, 1], [0, 0, 0, 1]],
[[0, 0, 255, 1], [0, 0, 255, 1], [0, 0, 0, 1]]
]
buff = io.BytesIO()
plt.imsave(buff, input_img, format="png")
buff.seek(0)
read_img = plt.imread(buff)

# Need to multiply by 255 to adjust for normalization in imread()
read_img = (255*read_img).astype('uint8')

assert_array_equal(np.array(input_img), read_img)


def test_imsave_color_alpha():
# Test that imsave accept arrays with ndim=3 where the third dimension is
# color and alpha without raising any exceptions, and that the data is
Expand Down
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