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Commit605fd3c

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Merge pull request#10220 from Zac-HD/imshow-rgb-fixes
FIX: Clip float RGB data to valid range for imshow
2 parents2ed292d +7f97698 commit605fd3c

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7 files changed

+68
-7
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7 files changed

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@@ -0,0 +1,7 @@
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`Axes.imshow` clips RGB values to the valid range
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-------------------------------------------------
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When `Axes.imshow` is passed an RGB or RGBA value with out-of-range
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values, it now logs a warning and clips them to the valid range.
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The old behaviour, wrapping back in to the range, often hid outliers
7+
and made interpreting RGB images unreliable.

‎doc/users/credits.rst

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Original file line numberDiff line numberDiff line change
@@ -386,6 +386,7 @@ Yu Feng,
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Yunfei Yang,
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Yuri D'Elia,
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Yuval Langer,
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Zac Hatfield-Dodds,
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Zach Pincus,
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Zair Mubashar,
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alex,
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`Axes.imshow` clips RGB values to the valid range
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-------------------------------------------------
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When `Axes.imshow` is passed an RGB or RGBA value with out-of-range
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values, it now logs a warning and clips them to the valid range.
6+
The old behaviour, wrapping back in to the range, often hid outliers
7+
and made interpreting RGB images unreliable.

‎lib/matplotlib/axes/_axes.py

Lines changed: 10 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -5319,10 +5319,14 @@ def imshow(self, X, cmap=None, norm=None, aspect=None,
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- MxNx3 -- RGB (float or uint8)
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- MxNx4 -- RGBA (float or uint8)
53215321
5322-
The value for each component of MxNx3 and MxNx4 float arrays
5323-
should be in the range 0.0 to 1.0. MxN arrays are mapped
5324-
to colors based on the `norm` (mapping scalar to scalar)
5325-
and the `cmap` (mapping the normed scalar to a color).
5322+
MxN arrays are mapped to colors based on the `norm` (mapping
5323+
scalar to scalar) and the `cmap` (mapping the normed scalar to
5324+
a color).
5325+
5326+
Elements of RGB and RGBA arrays represent pixels of an MxN image.
5327+
All values should be in the range [0 .. 1] for floats or
5328+
[0 .. 255] for integers. Out-of-range values will be clipped to
5329+
these bounds.
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53275331
cmap : `~matplotlib.colors.Colormap`, optional, default: None
53285332
If None, default to rc `image.cmap` value. `cmap` is ignored
@@ -5364,7 +5368,8 @@ def imshow(self, X, cmap=None, norm=None, aspect=None,
53645368
settings for `vmin` and `vmax` will be ignored.
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53665370
alpha : scalar, optional, default: None
5367-
The alpha blending value, between 0 (transparent) and 1 (opaque)
5371+
The alpha blending value, between 0 (transparent) and 1 (opaque).
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The ``alpha`` argument is ignored for RGBA input data.
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53695374
origin : ['upper' | 'lower'], optional, default: None
53705375
Place the [0,0] index of the array in the upper left or lower left

‎lib/matplotlib/cm.py

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -259,7 +259,7 @@ def to_rgba(self, x, alpha=None, bytes=False, norm=True):
259259
xx= (xx*255).astype(np.uint8)
260260
elifxx.dtype==np.uint8:
261261
ifnotbytes:
262-
xx=xx.astype(float)/255
262+
xx=xx.astype(np.float32)/255
263263
else:
264264
raiseValueError("Image RGB array must be uint8 or "
265265
"floating point; found %s"%xx.dtype)

‎lib/matplotlib/image.py

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -13,6 +13,7 @@
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frommathimportceil
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importos
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importlogging
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importnumpyasnp
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@@ -34,6 +35,8 @@
3435
frommatplotlib.transformsimport (Affine2D,BboxBase,Bbox,BboxTransform,
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IdentityTransform,TransformedBbox)
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38+
_log=logging.getLogger(__name__)
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# map interpolation strings to module constants
3841
_interpd_= {
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'none':_image.NEAREST,# fall back to nearest when not supported
@@ -623,6 +626,23 @@ def set_data(self, A):
623626
orself._A.ndim==3andself._A.shape[-1]in [3,4]):
624627
raiseTypeError("Invalid dimensions for image data")
625628

629+
ifself._A.ndim==3:
630+
# If the input data has values outside the valid range (after
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# normalisation), we issue a warning and then clip X to the bounds
632+
# - otherwise casting wraps extreme values, hiding outliers and
633+
# making reliable interpretation impossible.
634+
high=255ifnp.issubdtype(self._A.dtype,np.integer)else1
635+
ifself._A.min()<0orhigh<self._A.max():
636+
_log.warning(
637+
'Clipping input data to the valid range for imshow with '
638+
'RGB data ([0..1] for floats or [0..255] for integers).'
639+
)
640+
self._A=np.clip(self._A,0,high)
641+
# Cast unsupported integer types to uint8
642+
ifself._A.dtype!=np.uint8andnp.issubdtype(self._A.dtype,
643+
np.integer):
644+
self._A=self._A.astype(np.uint8)
645+
626646
self._imcache=None
627647
self._rgbacache=None
628648
self.stale=True

‎lib/matplotlib/tests/test_image.py

Lines changed: 22 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -620,7 +620,7 @@ def test_minimized_rasterized():
620620
deftest_load_from_url():
621621
req=six.moves.urllib.request.urlopen(
622622
"http://matplotlib.org/_static/logo_sidebar_horiz.png")
623-
Z=plt.imread(req)
623+
plt.imread(req)
624624

625625

626626
@image_comparison(baseline_images=['log_scale_image'],
@@ -813,6 +813,27 @@ def test_imshow_no_warn_invalid():
813813
assertlen(warns)==0
814814

815815

816+
@pytest.mark.parametrize(
817+
'dtype', [np.dtype(s)forsin'u2 u4 i2 i4 i8 f4 f8'.split()])
818+
deftest_imshow_clips_rgb_to_valid_range(dtype):
819+
arr=np.arange(300,dtype=dtype).reshape((10,10,3))
820+
ifdtype.kind!='u':
821+
arr-=10
822+
too_low=arr<0
823+
too_high=arr>255
824+
ifdtype.kind=='f':
825+
arr=arr/255
826+
_,ax=plt.subplots()
827+
out=ax.imshow(arr).get_array()
828+
assert (out[too_low]==0).all()
829+
ifdtype.kind=='f':
830+
assert (out[too_high]==1).all()
831+
assertout.dtype.kind=='f'
832+
else:
833+
assert (out[too_high]==255).all()
834+
assertout.dtype==np.uint8
835+
836+
816837
@image_comparison(baseline_images=['imshow_flatfield'],
817838
remove_text=True,style='mpl20',
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extensions=['png'])

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