Re: [Matplotlib-users] Two circles with “exponential decay” coloring, and alpha < 1, having trouble with color mixing?

[Thomas Caswell]

The way we do the alpha blending, the output value is (alpha * v1) +
((alpha-1) * v2).  All of the artists are compsited down on top of a white
background so the compositing is not commutative.

(a * .5) + (.5 * (b * .5 + .5))  =/= (b * .5) + (.5 * (a * .5 + .5))


On Mon, Nov 23, 2015 at 1:55 PM Sterling Smith 
wrote:

> Maybe the issue is with the colormap not having an alpha?  Does this
>
> http://stackoverflow.com/questions/10127284/overlay-imshow-plots-in-matplotlib
> help?
>
> Otherwise, you might file a bug at
> https://github.com/matplotlib/matplotlib/issues/new
>
> -Sterling
>
> On Nov 20, 2015, at 4:46PM, Brian Merchant  wrote:
>
> > Hi all,
> >
> > In order to get circles such that their coloring is radially symmetric,
> with center being the darkest, and exponential decay in color as one moves
> farther away from the center along the radius, I used imshow with clip_path
> using Circle patches.
> >
> > Here's a toy script that overlaps two such circles:
> https://gist.github.com/bmer/7063cc2dd09f1b80a252
> >
> > As you can see if you run the script (or, if you follow this link:
> http://i.imgur.com/H9jEAZ3.png), even though the alpha is set at 0.5,
> there doesn't seem to be proper "color mixing" occurring (we should see a
> result that is symmetric along the x-axis).
> >
> > Why is that, and what could I do to fix this issue?
> >
> > Kind regards,
> > Brian
> >
> --
> > ___
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> > Matplotlib-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/matplotlib-users
>
>
>
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Re: [Matplotlib-users] Two circles with “exponential decay” coloring, and alpha < 1, having trouble with color mixing?

[Sterling Smith]

Maybe the issue is with the colormap not having an alpha?  Does this
http://stackoverflow.com/questions/10127284/overlay-imshow-plots-in-matplotlib
help?

Otherwise, you might file a bug at 
https://github.com/matplotlib/matplotlib/issues/new

-Sterling

On Nov 20, 2015, at 4:46PM, Brian Merchant  wrote:

> Hi all, 
> 
> In order to get circles such that their coloring is radially symmetric, with 
> center being the darkest, and exponential decay in color as one moves farther 
> away from the center along the radius, I used imshow with clip_path using 
> Circle patches. 
> 
> Here's a toy script that overlaps two such circles: 
> https://gist.github.com/bmer/7063cc2dd09f1b80a252
> 
> As you can see if you run the script (or, if you follow this link: 
> http://i.imgur.com/H9jEAZ3.png), even though the alpha is set at 0.5, there 
> doesn't seem to be proper "color mixing" occurring (we should see a result 
> that is symmetric along the x-axis). 
> 
> Why is that, and what could I do to fix this issue? 
> 
> Kind regards, 
> Brian
> --
> ___
> Matplotlib-users mailing list
> Matplotlib-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users


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[Matplotlib-users] Two circles with “exponential decay” coloring, and alpha < 1, having trouble with color mixing?

[Brian Merchant]

Hi all,

In order to get circles such that their coloring is radially symmetric,
with center being the darkest, and exponential decay in color as one moves
farther away from the center along the radius, I used imshow with clip_path
using Circle patches.

Here's a toy script that overlaps two such circles:
https://gist.github.com/bmer/7063cc2dd09f1b80a252

As you can see if you run the script (or, if you follow this link:
http://i.imgur.com/H9jEAZ3.png), even though the alpha is set at 0.5, there
doesn't seem to be proper "color mixing" occurring (we should see a result
that is symmetric along the x-axis).

Why is that, and what could I do to fix this issue?

Kind regards,
Brian
--
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