I'm new in blender, thanks for the patience.


I have this simple volume shader I applied into this object (Images below), and I want to make a simple white colored background with composer.

Shader (Shader)

The white box is a primitive example object (Render without compositor)

The problem:

The only way I know how to make it is by using the alpha over + RGB nodes (Image below), but the shader objects get overwritten by the color. I think it's because the shader doesn't have any surface node connected.

Pink BG overwrite the shader (Render with compositor)


Is there another way to make it? Do i need to understand something to work propely?

  • $\begingroup$ if you're talking about your 3 objects on the right, it looks like they haven't been rendered, are you sure that they are visible for render? $\endgroup$
    – moonboots
    Jul 21, 2022 at 5:55
  • $\begingroup$ Yep they are, i've checked the "Disabled in renders" box and did a render text without the compositor, everything normal. Thanks for the response. $\endgroup$
    – OneNoBeing
    Jul 21, 2022 at 19:57
  • $\begingroup$ maybe share your file: blend-exchange.com $\endgroup$
    – moonboots
    Jul 21, 2022 at 20:10
  • $\begingroup$ I did it now :D $\endgroup$
    – OneNoBeing
    Jul 21, 2022 at 20:55
  • 1
    $\begingroup$ maybe read this page: developer.blender.org/T65993 $\endgroup$
    – moonboots
    Jul 21, 2022 at 21:18

1 Answer 1


Two of the three solutions are described by 'L0Lock', thanks for your effort.


The issue here is that Blender doesn't consider a volume with a density of zero can possibly affect the alpha as it's a volume that doesn't "exist".

Solution 1

So one way to fix that is to adapt your Principled Volume shader with some density that can be rendered:

demo shader fix

Here I just set the density to 1 and plugged your color ramp into the Principled Volume's color.

Solution 2

Alternatively, you can keep your shader, but instead of using the alpha pass for the Alpha Over's factor, you just use the beauty pass (the full combined "image"output from the render layer node) which has its own straight alpha. It's not ideal, but it works by simply leaving the factor input empty:

demo straight alpha

Solution 3

This one thanks to 'Game Abuse Studio' found here:


Actually this one worked better in my case. The basic here is that is a png render, and I added a background in post production.

Disclaimer: If you're a beginner like myself that don't know how to use the video editing and all the render properties, I can't solve one issue. When you group the image sequence and render, the transparency vanishes. But when I grouped in another software like Davinci Resolve worked very fine.

  • $\begingroup$ Solution 3 a bit far-fetched - and technically incorrect in terms of color preservation. Besides, it's literally answering the topic "Transparent background with compositing not working" by "don't use transparency". If you just need to put whatever color you want in the background, a sturdier and "correct" solution could be to set the color in your world shader. $\endgroup$
    – Lauloque
    Jul 26, 2022 at 15:18

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