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I'm on an AMD machine, so GPU rendering is off the table, but I don't mind a lengthy render as long as the end result is good.

So far I've tried:

  • Rendering at 5000 samples

  • Various indirect/direct clamp values

  • Increasing volume sampling max steps

  • increasing volume bounces (in light paths)

    And in all likelihood, a few things I've forgotten.

This render took 40 minutes with tons of settings cranked up, but still has a lot of visible noise despite being fairly small:

enter image description here

I'm using a volume scatter shader to add fog, one transparent plane using a procedural texture for the smoke.

It's worth noting that while I do not have a high-end machine, I also don't have a particularly horrible one either.

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    $\begingroup$ Have you tried setting the light path as diffuse ray? You can add a math node to control it $\endgroup$
    – 360ueck
    Jun 13, 2016 at 22:24
  • $\begingroup$ Have you tried decreasing the Light Path bounces to something tiny, like 1, 2, or 3 MAX? This will mean that Blender has to work less to render, because rays that don't find a light source are terminated more quickly. Less bounces always leads to quicker rendering. I might suggest Max: 3, Min: 0, Diffuse: 2, Glossy: 2, Transmission: 3, Volume: 2. P.S. If you include a .blend file, I can look into it more in depth. $\endgroup$
    – Shady Puck
    Jun 13, 2016 at 22:47
  • $\begingroup$ I've tried it at 0 and at 4. I'm not so much concerned that my renders are taking too long. What I'm trying to figure out is what I need to change to make the noise go away. I've cranked up a ton of values and reduced my render size yet the noise remains. Here's the .blend file: dropbox.com/home?preview=Darkspire1.blend1 $\endgroup$
    – Joshua King
    Jun 13, 2016 at 23:00

1 Answer 1

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You can switch to branched path tracing and use its subsample controls. Increasing subsurface sample level will improve noise for SSS, volumes for volume scatter effects Note that volume samples only affect indirect light, meaning the noise that comes from volume bounces being > 0. For other volume noise, adjust lamp sampling values.

See this question for general info about branched path: What is branched path tracing and how is it useful?

I normally recommend using the "square samples" option with branched path, as it allows you to work with simpler values when juggling all the subsample counts. "square samples" just, well, squares all the values being used for sample counts. So "4" samples becomes 4*4=16 samples. The reason for this is the more samples you have, the more samples you need to add to get a noticeable difference. By adjust sample counts in increments of squares, you ensure you're always getting a statistically significant addition for each sample level.

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  • $\begingroup$ Thanks. Amazing how long volume scatter takes when applied to the world shader. $\endgroup$
    – Joshua King
    Jun 17, 2016 at 20:36

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