I made a fire simulation in Blender. Then I rendered it as a png sequence with transparent background. Now I want to composite this fire into some real footage (the camera movement is already matched). But I can't find out how I can make the fire shine a glow onto my actor in the footage. I am using Davinci Resolve, and have already tried the Light rays effect. But my problem is that I can only give it one colour and I can't use the fire footage as the colour source.

I know that this is the Blendr site but I could find a better place to ask my question. If it is unappropriated over here please point that out.

  • $\begingroup$ There is a designated blackmagic davinci forum, tried that? $\endgroup$ – Leander May 24 '20 at 14:45
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    $\begingroup$ Can’t be done with PNG! PNG is the worst, most poorly designed file format. Don’t use it. $\endgroup$ – troy_s May 24 '20 at 15:43
  • $\begingroup$ Why PNGs don't work for this: Render semi-transparent volume with cycles with a great explanation by mr. brecht himself. $\endgroup$ – Jachym Michal May 24 '20 at 15:58
  • $\begingroup$ @troy_s On behalf of everyone, thank you for opening our eyes about PNGs :). $\endgroup$ – Jachym Michal May 24 '20 at 16:16
  • $\begingroup$ The more folks who understand the basics of pixel encodings, the better. In more specific terms for folks trying to do things with proper light transport concepts, PNG is an absolutely crippling encoding. This answer (blender.stackexchange.com/a/148466/213) from Robert G deserves infinite upvotes for more reasons to avoid PNG like the plague. $\endgroup$ – troy_s May 24 '20 at 20:50

Why did you give up on using EXR (I have tried to import EXR files to Davinci Resolve with the LUT's) and go to a useless format like PNG? PNG cannot handle associated alpha channel, it cannot have pixels that are emissive and transparent at the same time.

Go back to EXRs and be happy.

As for the glow on other elements you have two choices: Create some geometry in blender that will be affected by the fire and use it to add luminance to the scene in the compositor of your choice (fusion can do that) or even as a video track over the original footage in davinci. Or use masks on the footage and selective color correction and try to recreate the effect on other elements of the scene.

In the world of movie-making, such scenes are shot with the special effect in mind, usually having lights that flicker and simulate the color and brightness of the fire. You will find out that it is hard to replicate after the fact. The intensity, direction and movement of the shadows to make a convincing effect will require a lot of work if it was not done in the original plate.

  • $\begingroup$ Yes sorry I mixed it up I am going to use EXR in the final version. And okay I will try it with masks. $\endgroup$ – Phönix 64 May 24 '20 at 16:41

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