Rendering lots of metal

[cheerioboy]

Hi,

I'm rendering a few scenes that are composed entirely of metal objects. glossiness is usually around .9 with 8 subdivs. Dome (w/hdri) and planar vray lights are all used with 8 subdivs. GI is turned off. Any suggestions for optimizing a scene like this? I've been playing with upping the light subdivs, the materials subdivs and render settings (Adaptive subdivision, min-2 / max-4) and getting anything decent seems to take a lot of time. Currently around an hour per frame, 1080p.

Where might to focus on tweaking to optimize render time/quality?

cheers

[samuel_bubat]

Turning down the reflection depth decreases the rendertime. Values of 2-3 are usually enough for glossy materials.

[joconnell]

For starters use adaptive dmc with low anti aliasing samples (start with 1-4) and up your material samples instead up to higher values. Try doubling the values each time until you get clean results, then gradually pare back. What also helps a lot is enabling a few of the render elements so you can see where your noise is. Total lighting will give you all of the diffuse in the scene so you can see if your lights are noisy in terms of shading, shadows to again see if your lights are noisy and then reflection and specular to see how your materials are doing in terms of cleanliness. Your anti aliasing sampler will make a big difference too, if you use a sharp filter like mitchell or catmull, it'll make the noise even more apparent so something like area or quadractic while softer will help hide the noise. Since your rendering HD you don't need to worry about losing detail. A big factor is also the dynamic range of your scene, if you're using a hdri map with lots of really high values and really low values so that it covers a wide range of exposure, this can be hard work for the sampler in areas where light and dark meet. You can try turning on clamp output to something like 2 in the colour mapping dialog and also turn on sub pixel mapping. They'll both make your renders a tiny bit less bright and it'll give you less to work with if you're rendering to exr and compositing in float, but it'll make it far easier on the sampler and give you cleaner results quicker.

Post motion blur and depth of field will of course soften the lot while adding quality to the renders so it's a nice way to clean things up too.

[rivoli]

For starters use adaptive dmc with low anti aliasing samples (start with 1-4) and up your material samples instead up to higher values.

what john says. dmc works much better than subdivisions, especially in scenes where there are a lot of glossy effects. as your main concern are the reflections, I'd try as he suggests, low image sampler settings, a noise threshold of around 0,005, and I'd try to manage the noise with the material subdivisions.

[cheerioboy]

these are great comments, thanks guys

@samuel_bubat
already been doing that good sir, I had a reflection depth of 4, dropped to 3

@joconnell
great comments, I'm already seeing a decrease in the render time but there is a bit more noise. But at least now it seems like scene is manageable through just tweaking the materials. nice!

@rivoli
thanks for chiming in, totally working this angle and already the render time is cut in half. I think the noise is reasonable.

question. since total lighting looks to be black can I just decrease light subdivisions, or will it make no difference if there's no diffuse to affect?

thanks again!

[joconnell]

Yep that's quite possible alright - for materials that are either reflective black or 100% reflective like chromes, they don't have any diffuse to them whatsoever so you get no benefit by putting in lights at all. If you only have these type of materials in your scene you might be better off using a sphere with your hdri mapped inside it and have no lights being added to the render overhead. The rule with vray is that the less something contributes to the final render, the less sampling vray will do on it. So for example if you have an object with a tiny bit of reflection (maybe the surface is 5% reflective) then vray won't bother putting many samples for that object since it only adds 5% to the final pixels.

What you want to do is again see where the noise is by using the various render passes to chase it down. If you've dropped it down to only being the materials then you can either up their material settings as you're currently doing, or figure out a way to make it easier for them to sample what they're reflecting. If your only source of reflection is a hdri and all of the materials in the scene are blurry, you could pre blur the hdri a tiny amount to make it simple for vray to sample it and get cleaner results in less time. Alternatively try using the clamp output controls / sub pixel mapping to cut down the really bright values in the render before vray does it's final sampling to get things less physically correct, but again easier to get a clean result.

[cheerioboy]

This is great info, a drawback i find to using geometry cards instead of lights is that I can't selectively pick out objects to include/exclude. If I remove the samples from the light does that essentially make it a card?

I'm already seeing results having moved the HDRI from the dome light to the environment reflection slot of the vray rollout.

[rivoli]

you can uncheck affect diffuse for any light you want, and have them affecting only the reflections/speculars, but if there's any shadow casting in scene then you don't want to go too low with the lights subdivisions. it's much faster to get clean shadows tweaking the sampling per light, than trying to do that with the image sampler.