Improve handling of alpha when saving to jpeg. #15437
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Temporarily changing the figure background and manually calculating the alpha-shading towards white is more low-level. It's harder to understand what's going on and it might be more susceptible of introducing bugs in the future.
Is the performance gain worth it?
| @@ -563,23 +563,26 @@ def print_jpg(self, filename_or_obj, *args, dryrun=False, pil_kwargs=None, | |||
| `PIL.Image.save` when saving the figure. These take precedence | |||
| over *quality*, *optimize* and *progressive*. | |||
| """ | |||
| FigureCanvasAgg.draw(self) | |||
| if dryrun: | |||
| return | |||
| # The image is "pasted" onto a white background image to safely | |||
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The comment needs to be adapted.
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well, this is still pasting the figure over a white background.
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Actually, another motivation for the change is to make buffer_rgba() return an array that can be directly passed to imsave() -- essentially doing the same thing as in #15435, but for jpeg. |
| @@ -563,23 +563,25 @@ def print_jpg(self, filename_or_obj, *args, dryrun=False, pil_kwargs=None, | |||
| `PIL.Image.save` when saving the figure. These take precedence | |||
| over *quality*, *optimize* and *progressive*. | |||
| """ | |||
| FigureCanvasAgg.draw(self) | |||
| # The image is "pasted" onto a white background to handle transparency. | |||
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I think the term "paste" is a bit misleading
| # The image is "pasted" onto a white background to handle transparency. | |
| # Remove transparency by alpha-blending on an assumed white background |
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sure, sounds good, edited accordingly
We can compose the figure facecolor against a white background before rendering the image, rather than after. This saves an image composition step.
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Will this cause weird flickering on interactive views (maybe not regular figures that composite on white, but embedded/notebook/something else)? |
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I'm not sure why it would? |
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I was thinking of stuff like changing the DPI, but I see setting the canvas manager is handled in the call stack above this one. |
We can compose the figure facecolor against a white background before
rendering the image, rather than after. This saves an image composition
step.
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