luxus fireflies problem
Ademnus
Posts: 744
with mirrored surfaces, I keep getting speckles and "fireflies" in the reflections. I did some digging and some folks solved the problem but neglected to detail quite how -also they were using lux with blender. Not sure if that matters.
If anyone knows what settings clear this up, id sure appreciate it.
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I have a few thoughts here.
How long have you left the image render? Have you tried dropping the refleciton colour down a little from pure white? Have you set the "outlier rejection constant" in the render settings to at least one? Are you using metropolis (do so if not).
I've tried short term and long term render times. I will try dropping the reflection color and changing the outlier constant setting. I am using linear instead of metro. I'll let you know how those changes work out.
outlier is set to 5 by default. too high? also, what do you use if not metropolis? random, low discrepancy or erpt?
5 is actually very high and should reduce fireflies, but it will probably be slowing your renders down though. I really wouldn’t suggest using anything but metropolis unless you really know what you're doing. Using metropolis might be a little slower than some of the other samplers, but it works very well in a variety of situations.
If you have any materials in your scene that have their diffuse colour set to pure white you should change those down a little. If you have super glossy surfaces try bumping down the gloss. If your lights are bouncing multiple times before they hit your main subject I'd suggest moving your lights. Overly bright lights can also cause fireflys.
The mirror material in Lux is inherently noisy, and always takes a long time to clear up. Using SPPM instead of BiDir/Path can help it clear up more quickly, but SPPM has its own issues... Mirror also works better with strong lighting, in my experience. You may also need to increase the ray bounce limit, especially if you have multiple mirrors or other highly reflective surfaces in the scene. (See In the Elevator for the ultimate mirror material torture test; even at 7500S/p, the mirror surfaces still have a lot of noise in them.)
Even though it was rendered with BiDir, I set a refine brush mask about half-way through the 6500S/p for Whip Dom 001 (NSFW) to get Lux to focus on the mirror reflection, which helped the mirror clear up.
For mirror material, I always set the reflection colour to pure white; like glass, it's one of the materials that doesn't follow the "don't use an albedo above .8" rule. (In fact, LuxRender's internal default for the mirror material's Kr parameter is pure white.) You'd use a lower value to simulate a dirty mirror (more likely with a texture map that is mostly white with gray smudges for the dirt areas).
can you explain what settings I'd need to change to achieve this? Im not even sure I know what BiDir is lol. Real luxus newbie here.
I use Reality, so I'm not familiar with how to specify the surface integrator in Luxus. It's presumably somewhere in the global render settings. BiDir might very well be the default, though, as it's generally the preferred integrator to use, unless you are using GPU acceleration, in which case it is completely borked (even by the Lux devs' own admission) and you should use Path. The surface integrator is also where you specify the max ray bounce count (eyedepth and lightdepth for BiDir, maxdepth for Path).
For the mirror material, set the reflection value to pure white. I'd also recommend setting thin film thickness to 0 to disable thin film.
Then, for the refine brush, that's part of the LuxRender user interface. The third sub-tab of the Render tab lets you paint a refinement area (don't forget to click apply after you are done painting the areas you want Lux to focus on). Use of the refinement brush with BiDir can actually harm your image (seen as splotching on surfaces), however, since it only impacts the eye path and not the light path. So let your render go for a while with no refinement painted to get the non-mirror parts to clear up sufficiently. Then rename the .flm file so you can revert in case refinement makes things worse with your BiDir image (you don't have to stop Lux, just do the rename shortly after the film write interval completes -- the next time the interval comes around, you'll end up with two film files), then paint in and apply the refinement in the mirror area.
Dont use mirror. Use metal instead and set the gloss up very high.
Btw, showing a render of what your getting will also help get better tips cause there is a lot in a render that needs to be considered when working with LuxRender
Unfortunately, the metal material, even at its shiniest, doesn't offer much in the way of reflections. There's shiny metal (available in Luxus), which is a bit better, but if you genuinely want reflections you need mirrors. The reason for this is because the regular metal materials have microfacets which act as a coating and break up the reflections. Mirrors work like shiny metal but minus this micro-faceting.
Mirrors by themselves won't generally cause fireflies. This is down to the overall scene complexity and how much your light needs to travel. If your mirror is facing similarly specular objects, then be aware that light may bounce several times between the two surfaces, which can cause the fireflies in a render. This can happen with just about any surface, not just glossy and metal surfaces, so be sure to check your specular values.
Details on how the scene is put together will help us root out the cause of the problem, and how it can be avoided or fixed.