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imsave should preserve alpha channel #1956

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merged 1 commit into from May 3, 2013
Merged

imsave should preserve alpha channel #1956

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2 changes: 1 addition & 1 deletion lib/matplotlib/image.py
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Expand Up @@ -1273,7 +1273,7 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
fig = Figure(figsize=figsize, dpi=dpi, frameon=False)
canvas = FigureCanvas(fig)
im = fig.figimage(arr, cmap=cmap, vmin=vmin, vmax=vmax, origin=origin)
fig.savefig(fname, dpi=dpi, format=format)
fig.savefig(fname, dpi=dpi, format=format, transparent=True)


def pil_to_array( pilImage ):
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19 changes: 11 additions & 8 deletions lib/matplotlib/tests/test_image.py
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Expand Up @@ -5,7 +5,7 @@
from matplotlib import rcParams
import matplotlib.pyplot as plt
from nose.tools import assert_raises
from numpy.testing import assert_array_equal
from numpy.testing import assert_array_equal, assert_array_almost_equal

import io
import os
Expand Down Expand Up @@ -129,8 +129,9 @@ def test_imsave():
assert_array_equal(arr_dpi1, arr_dpi100)

def test_imsave_color_alpha():
# The goal is to test that imsave will accept arrays with ndim=3 where
# the third dimension is color and alpha without raising any exceptions
# 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
# acceptably preserved through a save/read roundtrip.
from numpy import random
random.seed(1)
data = random.rand(256, 128, 4)
Expand All @@ -141,12 +142,14 @@ def test_imsave_color_alpha():
buff.seek(0)
arr_buf = plt.imread(buff)

assert arr_buf.shape == data.shape
# Recreate the float -> uint8 -> float32 conversion of the data
data = (255*data).astype('uint8').astype('float32')/255
# Wherever alpha values were rounded down to 0, the rgb values all get set
# to 0 during imsave (this is reasonable behaviour).
# Recreate that here:
data[data[:, :, 3] == 0] = 0

# Unfortunately, the AGG process "flattens" the RGBA data
# into an equivalent RGB data with no transparency. So we
# Can't directly compare the arrays like we could in some
# other imsave tests.
assert_array_equal(data, arr_buf)

@image_comparison(baseline_images=['image_clip'])
def test_image_clip():
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