[yt-dev] Issue #873: volume rendering set_background does not work (yt_analysis/yt)

[Michael Zingale]

Hi Cameron, this answers a question I've had for a white, since I've been
trying to get a white background.  Two comments on the new cookbook recipe
you just posted -- are you sure that "up" is "up" in those images?  When I
use write_png, my image is upside down.  Secondary, do we want to try to
pass the transparent/white background stuff through the draw_domain and
save_annotated functions?  At the moment, draw_domain forces things to be
black, and save_annotated sets the facecolor of the resulting plot to black.

Mike


On Thu, Jul 31, 2014 at 12:12 AM, Cameron Hummels <
issues-reply at bitbucket.org> wrote:

> New issue 873: volume rendering set_background does not work
>
> https://bitbucket.org/yt_analysis/yt/issue/873/volume-rendering-set_background-does-not
>
> Cameron Hummels:
>
> I tried to make a VR with different background colors by combining the two
> cookbook recipes:
>
>
> http://yt-project.org/docs/dev-3.0/cookbook/simple_plots.html#image-background-colors
>
> http://yt-project.org/docs/dev-3.0/cookbook/simple_plots.html#simple-volume-rendering
>
> The resulting script is here:
>
> http://paste.yt-project.org/show/4978/
>
> Unfortunately, the 'background' keyword for `write_png` doesn't seem to
> work on real VRs.  All of the options end up yielding the original
> all-black background.
>
> When I dug into the code to figure out what was going on, it appears the
> problem is that the color channels are being normalized by the opacity
> channel prior to adding in the background color, and then renormalized by
> 1-opacity afterwards.  The VRs produced by the standard recipe yield a
> opacity=1 uniformly across the image, which essentially wipes out any
> changes from the renormalization.
>
> I can rip out this renormalization, or replace it with a rescale()
> function, but I wanted to make sure that wouldn't break other things.
>  Maybe this isn't worth changing since VR is getting a makeover soon.
>
>
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>



-- 
Michael Zingale
Associate Professor

Dept. of Physics & Astronomy • Stony Brook University • Stony Brook, NY
11794-3800
*phone*:  631-632-8225
*e-mail*: Michael.Zingale at stonybrook.edu
*web*: http://www.astro.sunysb.edu/mzingale
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