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UPDATE: This is solved! Check the comments for the solution.

What I see in my render view is not what I am getting on my exported image.

Attached are three screenshots:

  1. This is what I see in my render view (color+alpha). All looks good here.

  2. This is what the alpha channel looks like when isolated. This seems to be the culprit.

  3. This is what my exported image looks like. This occurs with any file type that supports alpha (png, tiff, etc).

I'm not sure if this is a bug or not.

Here is a link to my blender project file:

https://www.dropbox.com/s/rzv92bht4j9jdu8/4692%20break2%20230711.blend?dl=0

The collection titled "Black Hole" contains what you see in the screenshots.

Any help is greatly appreciated.

color and alpha

alpha only

final export

Thrash632
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  • I can see the problem in the first image as well where "all looks good". The colors of the accretion disk are getting darker and fading to black. The alpha is only fully transparent where it is completely black, each grey to white value above 0 is semi-transparent and shows the color of the semi-transparent part. If this is black or dark purple this might not be looking too bad on a black or dark background, but of course it is very visible on a white background. – Gordon Brinkmann Jul 12 '23 at 08:16
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    The next thing is, since this is not simply a transparent surface, but an emissive volume, you have the next problem that the PNG image file format (and TIFF neither at 8 bits) cannot store emission that is transparent. Transparent emission is added onto the underlying image, brightening it. More on this topic here: https://blender.stackexchange.com/questions/173932/exr-color-difference-to-png and here: https://blender.stackexchange.com/questions/179730/compositing-fire-into-footage-with-davinci-resolve – Gordon Brinkmann Jul 12 '23 at 08:42
  • Thanks for the feedback. This helped me understand the logic behind the resulting exports. I also found a video that provides a compositing node tree that solves this problem:

    https://www.youtube.com/watch?v=wNnFfXxB2Dg

    Just make sure to set the "Set Alpha" node to "Replace Alpha" instead of the default "Apply Mask".

     – Thrash632 Jul 12 '23 at 20:06
  • UPDATE: I also didn't add the blur node he added in the video linked above. In my case it just works better without it. – Thrash632 Jul 12 '23 at 20:41

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