LuxCoreRender Forums

Hello!

I've been playing around with very simple scenes (material spheres with car paint / glossy shaders, ground, sky light and/or lamps). I really like the reactivity in the viewport, it's night and day compared to LR 1.7! Starting the render is almost instant, and pretty stable.

However, the sampling never seems to converge... All the glossy reflections are noisy as hell after 500 sample and 1min30sec on a GTX Titan X... In comparison, a similar scene in Cycles is almost noise-free after 10 seconds.

I watched the SSS tutorial and he can get a decent renders of the dragon after 30 seconds, so I think there is something going on here.

I'm using path tracing, GPU render, other settings are set to default. Tried playing with the importance of the light with no luck.

Any idea?

chafouin wrote: ↑Wed Jan 24, 2018 9:55 pm Any idea?

If you are used to Cycles, you may be using some not (physically) correct values: for instance, users coming from some other render lean to use colors like (1.0, 1.0, 1.0) instead of (0.75, 0.75, 0.75). But it is hard to tell looking only at a rendering, if you post a test scene, we could be more specific.

Also, variance clamping is can a huge help to reduce noise, check this video, it is a bit old but should give you an idea: https://www.youtube.com/watch?v=9KqzfxgMRuA

Hey Dade,

I'm not using super bright diffuse values, it's just a glass shader, a car paint (BMW 339 preset) and a red glossy material (I've tried making the red darker as well, just in case).
I have played with the clamping already, the Optimal value calculated is 1307734, but I find that I can lower it to 50 without clamping too much, that's a pretty big difference It definitly helps with the noise, but it's still quite grainy. I'm using a Pixel filter of 1.5.

Tried 2000 samples but of course there is a point where adding much more samples does very little difference. The grain is acceptable but it's still a slow render (6 minutes) and would still need to be denoised. This performance seems very far from what I have seen in tutorials, or even my very old tests with SLG.

I noticed that during the viewport render, my GPU load is 21%. Is the viewport ernder only using the CPU? It's written RT Path CPU + RT Path Sampler.
The final render uses my GPU entirely, so it's not the problem.

I need to clean up the scene before sending it, I'll try to do it tomorrow (I have a lot of textures from plugins in my blender start scene, I'd prefer to not share them out of respect for the persons who sell them).

Thanks!

chafouin wrote: ↑Wed Jan 24, 2018 11:19 pm I noticed that during the viewport render, my GPU load is 21%. Is the viewport ernder only using the CPU? It's written RT Path CPU + RT Path Sampler.

Yes, it is currently only using the CPU.

Pretty impressive speed for a CPU preview!

I am suspecting caustics.

Clamping pretty much resolves it. But it then introduces darkening which consequently also diminishes dispersion (& even setting a tiny amount becomes useless; ie. glass becomes orange-reddish).

note: bellow the sphere are glasses

Keep in mind that caustics/dispersion are more a job for BIDIRCPU+METROPOLIS than for path tracers (PATHCPU or PATHOCL). They are the kind of details path tracers have very hard time to render.

Infact, it may be better to remove caustics all together when using PATH: by disabling light source "indirect visibility".

Yup, am aware... just leaving a note if anyone stumbles wondering: "WTH?!?"

Also, would be nice to have checkbox options to activate/deactivate refractive & reflective caustics as are in Cycles ('Filter Glossy' would also be nice).

Thanks.

kintuX wrote: ↑Thu Jan 25, 2018 2:10 pm Also, would be nice to have checkbox options to activate/deactivate refractive & reflective caustics as are in Cycles ('Filter Glossy' would also be nice).

There is something similar but it is in the light source panel: you can disable caustics on a per light source base. It should be similar to what Cycles does.

Can't see the "Indirect visibility" option in the light panel, is it somewhere else? Maybe it's not the philosophy of LuxRender, but would you consider setting the caustics off as a default, and let the user enable them if he needs them?

I tried BIDIR+METRO but performance is far worse. I'm attaching the scene if you want to look at it.