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Properly handle transparency for animations #5415

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Properly handle transparency for animations #5415

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30c2a09
Add 'flatten' kwarg to backend_agg savefig for print_png and print_ra…
cbreeden Nov 6, 2015
b8175a1
Fix width/height locations, and forgot to add alpha layer to flatten_…
cbreeden Nov 6, 2015
2fa1889
Move flatten_rgba to image.py and implment flatten_rgba for jpeg files.
cbreeden Nov 6, 2015
e0f1fd8
Removed typo
cbreeden Nov 6, 2015
d5fbd89
Clarify comment
cbreeden Nov 6, 2015
a57be1f
Appease the PEP8 gods. Somewhat of a sacraficial lamb if you ask me.
cbreeden Nov 6, 2015
0193d55
Add tests for flatten kwarg
cbreeden Nov 7, 2015
b2c4560
Fix typo in tests
cbreeden Nov 7, 2015
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Fix width/height locations, and forgot to add alpha layer to flatten_… 
…rgba
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@cbreeden
cbreeden committed Nov 25, 2015
commit b8175a144dbe4bcde6aa1ac05f9e56ba59b61bef
9 changes: 5 additions & 4 deletions lib/matplotlib/backends/backend_agg.py
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Expand Up @@ -542,13 +542,14 @@ def flatten_rgba(self, src, bg=None):

alpha = src[:,:,3]
src_rgb = src[:,:,:3]
h, w, _ = src.shape
w, h, _ = src.shape

result = np.empty((h,w,4))
result = np.empty((w, h, 4))
result[:,:,0] = (255 - alpha)*bg[0] + alpha*src_rgb[:,:,0]
result[:,:,1] = (255 - alpha)*bg[1] + alpha*src_rgb[:,:,1]
result[:,:,2] = (255 - alpha)*bg[2] + alpha*src_rgb[:,:,2]
result = (result/255).astype(np.uint8)
result[:,:,3] = 255
return result

def print_png(self, filename_or_obj, *args, **kwargs):
Expand All @@ -566,8 +567,8 @@ def print_png(self, filename_or_obj, *args, **kwargs):
if kwargs.get('flatten', False):
w, h = int(renderer.width), int(renderer.height)
img = renderer._renderer.buffer_rgba()
img = np.array(memoryview(img))
img = self.flatten_rgba(img).reshape((h, w, 4))
img = np.array(memoryview(img)).reshape((h,w,4))
img = self.flatten_rgba(img)
_png.write_png(img, filename_or_obj, self.figure.dpi)
else:
_png.write_png(renderer._renderer, filename_or_obj, self.figure.dpi)
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Minor point, but I think I like the way you organized the code in print_raw better than here: i.e. set a local variable img to the render contents and then optionally flatten it, ultimately passing img into write_png on a single line.

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@mdboom I really wanted to do that at first, but I will be honest when I say that I didn't understand what was going on here:

matplotlib/src/_backend_agg.cpp

Line 28 in 0037595

RendererAgg::RendererAgg(unsigned int width, unsigned int height, double dpi)
. I wasn't exactly sure if write_png needed something from that or not.

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No -- it shouldn't matter. _write_png just converts whatever is passed in to a numpy array.

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