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I have a problem with rendering fire with a transparent background. The preview is different from the saved image. How do I render a fire with a transparent background?

Preview and final result

Domain shader Domain Shader

Blender file:

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  • $\begingroup$ I haven't seen set fire like that, but can be correct. Can you share your simplified blend? We need to know more about your setup ... your shader is one thing, rendering emissive pixels above transparency another (blender.stackexchange.com/a/164940/2214) ... Output file format and setup another. Use blend-exchange.com ... your result looks like a combination of several of them. $\endgroup$
    – vklidu
    Apr 30, 2023 at 19:04
  • $\begingroup$ @vklidu I added a link to the blend file at the bottom of the post. $\endgroup$
    – Tobi
    May 1, 2023 at 11:28

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Under my 3.31 LTS version it works fine ...

enter image description here

Also in Compositor it works now better, than mentioned in my link in my comment above - Viewport was improved again, great :)

enter image description here


Now I'm just guessing ...

  • Your right image is not seen from blender's Render > Result window. (It is viewed in some other app were you added black background.) So explanation is that - PNG as output file format can't handle emissive data, so what you can see in your right image is a smoke part ... here the right side is over exposed to see smoke better in your screen. BTW in my compositor screen the Render Layer node can§t display emissive data as well :)

enter image description here

In this case is solution easy - save render as OpenEXR (Multilayered if needed), that is only one format that can handle all data needed for proper compositing later out of blender (sure in apps that can handle emissive data).

  • If your right image comes from blender - try to exclude GPU from rendering, so you can be sure issue is not based on your graphic card (but I would say in that case the result would be different).

  • Or in a case you are using some experimental build, try to use some official release.

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  • $\begingroup$ Oh thank you! I needed to save images in order to combine them later in the composer. The OpenEXR format is well suited for this. $\endgroup$
    – Tobi
    May 1, 2023 at 14:22

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