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  • Can't get rid of noise in smoke

    Doesn't seem to matter what I try, I can't get rid of the grainy noise in my interior Phoenix FD smoke simulation. I have reset the V-Ray renderer with the exception of turning off the time limit (set to 0). The scene is completely lit by indirect lighting; so a bounce from the sun on the floor, a mesh light on the ceiling, and three VrayLightMtl screens. What I don't understand is the smoke itself seems completely unaffected by the GI.

    When I look at the GI render element, the smoke is completely black in all situations, whether I set the Smoke Color > Scattering to be 'Ray-Traced', 'Disabled', 'Approximate', or 'Approximate+Shadows'. If I set it to Ray-Traced, the Light Cache calculation essentially freezes, estimating 6 hours to complete. I can't find a way around this, so I move on to Scattering > Disabled. The light cache now calculates quickly, same result with Approximate and Approximate + Shadows.

    If I do BF/LC, the whole scene is relatively noisy, claiming it'll be done in roughly 3 hours for the frame. The SampleRate element is largely white with some wide green/blue areas and red around the edges. All VrayLightMtl / Mesh Light items are rendered sharp and clear, but the rest of the scene (both Smoke) is still noisy and unusable, even through the scene. Smoke seems very dark for a constant color of white. After 20m I cancel it as it's still not usable after 135 passes.

    If I do IM/LC, the scene looks crystal clear but the smoke is noisy. SampleRate element shows scene mostly blue except VrayLightMtl items and smoke which are pure white with green edges. Smoke has same noise as before. From what I understand, white means it's still working on improving noise there so I let it go for 30m on it. No improvement in the noise so I cancel that one too.

    SO after a ton of reverting / tweaking I have discovered that there is no real way to address the noise in the actual smoke. Is there a setting somewhere I'm missing? I realize that putting direct lights on the smoke would improve the noise, but this scene is intentionally supposed to be dark.

    Thanks,
    Chris






  • #2
    Hey,

    Can you share a shot of how the smoke looks? Do you have the Phoenix Light Cache enabled? If you get dark artifacts with the size of a voxel, then turn it off. Disabled scattering will also produce darker image than approximate+shadows. Another thing you can try is to enable Probabilistic Volumetrics from the Phoenix Atmosphere settings.

    Cheers!
    Svetlin Nikolov, Ex Phoenix team lead

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    • #3
      Here are the images after 1 hour. V-Ray tells me that light cache won't work with progressive rendering so it would disable it anyways. I've also used Probablistic Volume as one of the many attempted repairs but it didn't do anything I'm enabling both now to see what happens.

      Edit: forgot to mention I added a Vray Ambient light in this particular render to try to help the noise issue, excluding everything but the simulator. I don't think it helped much or at all.
      Last edited by elyptic; 08-06-2017, 02:30 PM.

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      • #4
        Here is the render, complete after only ~10m. The smoke was ignored entirely in the samplerate screen, it only focused on the screens. Very noisy now, but at least it was fast. I'm unsure whether it's caused by the default 20 samples or the 3 GI samples. I had these at 32 each before but still had noise, will try again now.

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        • #5
          And this is with 6400 subdivs on the lightcache, 64 subdivs on each vraylightmtl, still noisy smoke. After the first few passes, I can see in the samplerate element that it barely works on the smoke at all.

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          • #6
            I should note that the settings of Phoenix are much more important to the speed of rendering than the V-Ray settings. Make sure you have the render step set to about 100 - for smoke this is quite enough. Set the shadow step to 200-300. If you don't find any significant quality issues, use Linear sampler instead of Spherical. Are you using any Phoenix displacement or do you have any texture maps? When adjusting the Probabilistic Volumetrics, you need the GI samples for your setup - make sure they are not too high and not too low - you need to hit a value somewhere in between. Especially if you set those too high, it will be more of a slowdown compared to turning probabilistic volumetrics off. Also, what grid resolution is the sim? If possible, please share the settings in the Rendering panel and the Volumetric Options. If this doesn't help, would removing all geometry and keeping just the lights and the simulator produce similar results? Would it be possible to send the scene over?

            Thanks very much!
            Svetlin Nikolov, Ex Phoenix team lead

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            • #7
              I am just using the default presets for those, alternating between cold smoke and large smoke, trying to find something that will render clean and fast. The step is 90% and shadow step is 200%. There is no phoenix displacement or texture. Grid resolution is about 1.5cm, and 4.5M cells in a tube shaped emitter. Unfortunately the only smoke the client likes is the ray traced scatter one which seems to take the longest.

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              • #8
                Hi Svetlin where can I email the scene for you to check it out?

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                • #9
                  I see - the ray-traced scattering is terribly slow, especially as the resolution increases. It would be best if you could send it over to Support@chaosgroup.com and I'll see if there is something that can be done via the settings or it requires code changes.

                  Thanks very much!
                  Svetlin Nikolov, Ex Phoenix team lead

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                  • #10
                    Can't send you the scene, it's 116MB unzipped and even when it's zipped it's too large (50MB) for your antivirus to scan lol

                    I'll email you a link to grab it.

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                    • #11
                      Roger that, thanks!
                      Svetlin Nikolov, Ex Phoenix team lead

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                      • #12
                        Hi Svetlin, I sent that wetransfer link almost a week ago but got notified it hasn't been retrieved yet! Please grab it soon before they delete it

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                        • #13
                          Hmm, support@chaosgroup.com, right? I'll ping the guys...
                          Svetlin Nikolov, Ex Phoenix team lead

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                          • #14
                            Hello,

                            Just went over your scene - you're using Volumetric Geometry mode (although it will provide you with the ability to use Render elements with Phoenix it is quite a bit slower than the Volumetric render mode). In addition you are using Spherical rendering sampler - this is the slowest method - you can try and use the Linear one.

                            Just a note - using the Volumetric mode with Raytraced scattering (which you are using) might make the building of V-Ray's Light Cache extremely long. We're aware of the issue and will fix it in a future version of PhoenixFD.

                            Thank you,
                            Last edited by georgi.zhekov; 19-06-2017, 09:03 AM.
                            Georgi Zhekov
                            Phoenix Product Manager
                            Chaos

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