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Keep the original dtype of the data when stretching #150

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merged 7 commits into from
Nov 20, 2023
+56 −25
Merged

Keep the original dtype of the data when stretching #150

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d34149c
Keep dtype when scaling the data
pnuu Nov 15, 2023
f23bb0c
Make sure stretching keeps the original dtype
pnuu Nov 15, 2023
b1d8d6f
Use float32 data for scale/offset attribute tests
pnuu Nov 16, 2023
5238b57
Ensure min and max stretch have the same dtype as the data
pnuu Nov 16, 2023
4b86901
Handle scalar stretch values
pnuu Nov 16, 2023
aee94f8
Refactor crude_stretch()
pnuu Nov 16, 2023
afc693a
Handle integer data in crude_stretch, refactor tests
pnuu Nov 17, 2023
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12 changes: 8 additions & 4 deletions trollimage/tests/test_image.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1456,7 +1456,7 @@ def test_gamma(self):

def test_crude_stretch(self):
"""Check crude stretching."""
arr = np.arange(75).reshape(5, 5, 3)
arr = np.arange(75, dtype=np.float32).reshape(5, 5, 3)
data = xr.DataArray(arr.copy(), dims=['y', 'x', 'bands'],
coords={'bands': ['R', 'G', 'B']})
img = xrimage.XRImage(data)
Expand All @@ -1467,11 +1467,15 @@ def test_crude_stretch(self):
enhs = img.data.attrs['enhancement_history'][0]
scale_expected = np.array([0.01388889, 0.01388889, 0.01388889])
offset_expected = np.array([0., -0.01388889, -0.02777778])
assert img.data.dtype == np.float32
np.testing.assert_allclose(enhs['scale'].values, scale_expected)
np.testing.assert_allclose(enhs['offset'].values, offset_expected)
np.testing.assert_allclose(red, arr[:, :, 0] / 72.)
np.testing.assert_allclose(green, (arr[:, :, 1] - 1.) / (73. - 1.))
np.testing.assert_allclose(blue, (arr[:, :, 2] - 2.) / (74. - 2.))
expected_red = arr[:, :, 0] / 72.
np.testing.assert_allclose(red, expected_red.astype(np.float32), rtol=1e-6)
expected_green = (arr[:, :, 1] - 1.) / (73. - 1.)
np.testing.assert_allclose(green, expected_green.astype(np.float32), rtol=1e-6)
expected_blue = (arr[:, :, 2] - 2.) / (74. - 2.)
np.testing.assert_allclose(blue, expected_blue.astype(np.float32), rtol=1e-6)

arr = np.arange(75).reshape(5, 5, 3).astype(float)
data = xr.DataArray(arr.copy(), dims=['y', 'x', 'bands'],
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4 changes: 2 additions & 2 deletions trollimage/xrimage.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1081,9 +1081,9 @@ def crude_stretch(self, min_stretch=None, max_stretch=None):
delta = (max_stretch - min_stretch)
if isinstance(delta, xr.DataArray):
# fillna if delta is NaN
scale_factor = (1.0 / delta).fillna(0)
scale_factor = (1.0 / delta).fillna(0).astype(self.data.dtype)
else:
scale_factor = 1.0 / delta
scale_factor = self.data.dtype.type(1.0 / delta)
attrs = self.data.attrs
offset = -min_stretch * scale_factor
self.data *= scale_factor
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