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imshow(..., alpha=0.5) produces different results in 2.x #6540
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- added this to the milestone on Jun 6, 2016
@mdboom, is this a result of the image architecture overhaul?
On Mon, Jun 6, 2016 at 1:47 AM, Elliott Sales de Andrade <
notifications@github.com> wrote:I think I have whittled this down sufficiently from the Cartopy example
that is failing. Running imshow(..., alpha=0.5) produces a different
result in 2.0.0b1 vs. 1.5.1 (both installed via conda.)import numpy as npimport matplotlib.pyplot as pltimport matplotlib as mpl
mpl.style.use('classic')
im = np.zeros((100, 100, 3), dtype=np.uint8)
plt.imshow(im, extent=(1, 10, 1, 10), alpha=0.5)
plt.xlim(0, 11)
plt.ylim(0, 11)plt.savefig('imshow_alpha.png')
Using 1.5.1:
[image: imshow_alpha_1 5 1]
https://cloud.githubusercontent.com/assets/302469/15812915/443b626e-2b88-11e6-89ca-14c0afbf4648.png
Using 2.0.0b1:
[image: imshow_alpha_2 0]
https://cloud.githubusercontent.com/assets/302469/15812917/4d8bc746-2b88-11e6-8e9f-68a37cd456d6.png
Using 2.0.0b1 with the classic style:
[image: imshow_alpha_2 0_classic]
https://cloud.githubusercontent.com/assets/302469/15812919/543d038e-2b88-11e6-9607-e80ae97955f6.pngGIMP tells me that the first is 50%, while the latter two are 75%.
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.I would be curious to know how the result compares with output from
gtkcairo.On Tue, Jun 7, 2016 at 11:32 AM, Benjamin Root ben.v.root@gmail.com wrote:
@mdboom, is this a result of the image architecture overhaul?
On Mon, Jun 6, 2016 at 1:47 AM, Elliott Sales de Andrade <
notifications@github.com> wrote:I think I have whittled this down sufficiently from the Cartopy example
that is failing. Running imshow(..., alpha=0.5) produces a different
result in 2.0.0b1 vs. 1.5.1 (both installed via conda.)import numpy as npimport matplotlib.pyplot as pltimport matplotlib as mpl
mpl.style.use('classic')
im = np.zeros((100, 100, 3), dtype=np.uint8)
plt.imshow(im, extent=(1, 10, 1, 10), alpha=0.5)
plt.xlim(0, 11)
plt.ylim(0, 11)plt.savefig('imshow_alpha.png')
Using 1.5.1:
[image: imshow_alpha_1 5 1]
https://cloud.githubusercontent.com/assets/302469/15812915/443b626e-2b88-11e6-89ca-14c0afbf4648.png
Using 2.0.0b1:
[image: imshow_alpha_2 0]
https://cloud.githubusercontent.com/assets/302469/15812917/4d8bc746-2b88-11e6-8e9f-68a37cd456d6.png
Using 2.0.0b1 with the classic style:
[image: imshow_alpha_2 0_classic]
https://cloud.githubusercontent.com/assets/302469/15812919/543d038e-2b88-11e6-9607-e80ae97955f6.pngGIMP tells me that the first is 50%, while the latter two are 75%.
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thread
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.I tried GTK3Cairo, but it's current broken:
Traceback (most recent call last): File ".../lib/matplotlib/backends/backend_gtk3cairo.py", line 45, in on_draw_event self._render_figure(w, h) File ".../lib/matplotlib/backends/backend_gtk3cairo.py", line 34, in _render_figure self.figure.draw (self._renderer) File ".../lib/matplotlib/artist.py", line 63, in draw_wrapper draw(artist, renderer, *args, **kwargs) File ".../lib/matplotlib/figure.py", line 1129, in draw renderer, self, dsu, self.suppressComposite) File ".../lib/matplotlib/image.py", line 139, in _draw_list_compositing_images a.draw(renderer) File ".../lib/matplotlib/artist.py", line 63, in draw_wrapper draw(artist, renderer, *args, **kwargs) File ".../lib/matplotlib/axes/_base.py", line 2373, in draw mimage._draw_list_compositing_images(renderer, self, dsu) File ".../lib/matplotlib/image.py", line 163, in _draw_list_compositing_images flush_images() File ".../lib/matplotlib/image.py", line 147, in flush_images image_group[0].draw(renderer) File ".../lib/matplotlib/artist.py", line 63, in draw_wrapper draw(artist, renderer, *args, **kwargs) File ".../lib/matplotlib/image.py", line 472, in draw renderer.draw_image(gc, l, b, im) File ".../lib/matplotlib/backends/backend_cairo.py", line 180, in draw_image im.shape[1]*4) TypeError: expected a writeable buffer objectIt looks like alpha is getting double applied?
- added a commit that references this issue on Jun 8, 2016
I think I have whittled this down sufficiently from the Cartopy example that is failing. Running imshow(..., alpha=0.5) produces a different result in 2.0.0b1 vs. 1.5.1 (both installed via conda.)
Using 1.5.1:
Using 2.0.0b1:
Using 2.0.0b1 with the classic style:
GIMP tells me that the first is 50%, while the latter two are 75%.