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Commit2236a2c

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Clip RGB data to vaild range in Axes.imshow
1 parent7ee6499 commit2236a2c

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6 files changed

+59
-7
lines changed

6 files changed

+59
-7
lines changed

‎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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@@ -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 issues 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
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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
@@ -5241,10 +5241,14 @@ 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)
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5244-
The value for each component of MxNx3 and MxNx4 float arrays
5245-
should be in the range 0.0 to 1.0. MxN arrays are mapped
5246-
to colors based on the `norm` (mapping scalar to scalar)
5247-
and the `cmap` (mapping the normed scalar to a color).
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MxN arrays are mapped to colors based on the `norm` (mapping
5245+
scalar to scalar) and the `cmap` (mapping the normed scalar to
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a color).
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5248+
Elements of RGB and RGBA arrays represent pixels of an MxN image.
5249+
All values should be in the range [0 .. 1] for floats or
5250+
[0 .. 255] for integers. Out-of-range values will be clipped to
5251+
these bounds.
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52495253
cmap : `~matplotlib.colors.Colormap`, optional, default: None
52505254
If None, default to rc `image.cmap` value. `cmap` is ignored
@@ -5286,7 +5290,8 @@ def imshow(self, X, cmap=None, norm=None, aspect=None,
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settings for `vmin` and `vmax` will be ignored.
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alpha : scalar, optional, default: None
5289-
The alpha blending value, between 0 (transparent) and 1 (opaque)
5293+
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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origin : ['upper' | 'lower'], optional, default: None
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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):
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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:
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raiseValueError("Image RGB array must be uint8 or "
265265
"floating point; found %s"%xx.dtype)

‎lib/matplotlib/image.py

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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 @@
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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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3740
# map interpolation strings to module constants
3841
_interpd_= {
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'none':_image.NEAREST,# fall back to nearest when not supported
@@ -621,6 +624,23 @@ def set_data(self, A):
621624
orself._A.ndim==3andself._A.shape[-1]in [3,4]):
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raiseTypeError("Invalid dimensions for image data")
623626

627+
ifself._A.ndim==3:
628+
# 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
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# - otherwise casting wraps extreme values, hiding outliers and
631+
# making reliable interpretation impossible.
632+
high=255ifnp.issubdtype(self._A.dtype,np.integer)else1
633+
ifself._A.min()<0orhigh<self._A.max():
634+
_log.warning(
635+
'Clipping input data to the valid range for imshow with '
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'RGB data ([0..1] for floats or [0..255] for integers).'
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)
638+
self._A=np.clip(self._A,0,high)
639+
# Cast unsupported integer types to uint8
640+
ifself._A.dtype!=np.uint8andnp.issubdtype(self._A.dtype,
641+
np.integer):
642+
self._A=self._A.astype(np.uint8)
643+
624644
self._imcache=None
625645
self._rgbacache=None
626646
self.stale=True

‎lib/matplotlib/tests/test_image.py

Lines changed: 20 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -602,7 +602,7 @@ def test_minimized_rasterized():
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deftest_load_from_url():
603603
req=six.moves.urllib.request.urlopen(
604604
"http://matplotlib.org/_static/logo_sidebar_horiz.png")
605-
Z=plt.imread(req)
605+
plt.imread(req)
606606

607607

608608
@image_comparison(baseline_images=['log_scale_image'],
@@ -795,6 +795,25 @@ def test_imshow_no_warn_invalid():
795795
assertlen(warns)==0
796796

797797

798+
@pytest.mark.parametrize(
799+
'dtype', [np.dtype(s)forsin'u2 u4 i2 i4 i8 f4 f8'.split()])
800+
deftest_imshow_clips_rgb_to_valid_range(dtype):
801+
arr=np.arange(300,dtype=dtype).reshape((10,10,3))
802+
ifdtype.kind!='u':
803+
arr-=10
804+
ifdtype.kind=='f':
805+
arr=arr/255
806+
_,ax=plt.subplots()
807+
out=ax.imshow(arr).get_array()
808+
assertout.min()==0
809+
ifdtype.kind=='f':
810+
assertout.max()==1
811+
assertout.dtype.kind=='f'
812+
else:
813+
assertout.max==255
814+
assertout.dtype==np.uint8
815+
816+
798817
@image_comparison(baseline_images=['imshow_flatfield'],
799818
remove_text=True,style='mpl20',
800819
extensions=['png'])

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