V-Ray Render Optimization - an in-depth Guide (call for Before/Afters)

[fewlo]

I must admit I've been guilty of being a slave to the sample rate pass, when as pointed out it is only a tool to understand where noise is coming from.

My render time is about 1:55 for a 1024x768 image. There's a slight bit of noise in the lighting and reflective passes, but very much acceptable. There is a LOT of red tho in the sample rate pass, particularly around the shadows and dark areas.

So my understanding is that with this scene you are happy with the results and level of noise but not the render time? The sample pass is telling you the aa is working too hard around the shadows and dark areas, so the theory is don't change anything with your settings except upping the lighting subdivs. This should lower the noise in those areas, lower the red bits in the sr pass and also lower the render time a bit.

Please anyone correct me if I'm wrong but I think I'm right?

[leejk]

No, my render time was fine, I was just questioning the importance of needing to get rid of the red in the sample rate pass. As someone else pointed out, it's just a tool and not the absolute gauge to drive the scene settings.

I did find the tutorial and this discussion very helpful, as it helped understand VRay much better.

[leejk]

One more question: when using the irradiance map for the primary GI engine, what's the correct way to remove noise in the GI pass? It seems that using it's presets have no effect.

[svetlozar.draganov]

The most important parameter for the IM quality is HSph. Subdivs. If you still got splotches even with High-preset begin increasing HSph.Subdivs value.
Interp.Samples value is also important for the quality, higher values will produce more smooth but less detailed illumination. You could try increasing this option as well but don't go too extreme with it.

[leejk]

The most important parameter for the IM quality is HSph. Subdivs. If you still got splotches even with High-preset begin increasing HSph.Subdivs value.
Interp.Samples value is also important for the quality, higher values will produce more smooth but less detailed illumination. You could try increasing this option as well but don't go too extreme with it.

I was looking at the presets listed in VRay 3.0 for the IR map, and no matter which preset you select the values all remain the same. Is this a bug?

I also tried bumping up the values as you mentioned, but still don't see any improvement thus far.

[svetlozar.draganov]

Changing IM presets should change the following parameters:

Min Rate / Max Rate / Color Threshold / Normals Threshold / Distance Threshold / Calc. Samples

If it doesn't please let us know the exact versions of Vray and 3DSMax you are using.

Would it be possible to send us an example of the GI splotches, along with its IM settings?

[leejk]

The presets are changing just as you described, however I am seeing no improvement in the GI pass. There's lots of noise that I can't figure out how to get rid of. The attached image is rendered using the IM high preset for the GI primary engine, light cache for the secondary, and dome light with subdivs at 64. The lighting element channel shows no noise.



If I switch the primary GI to Brute Force with subdivs at 256, still no improvement.

Final edit: After some more tweaking I discovered the culprit, the ambient occlusion settings. The radius was set to a high value; reducing it got rid of the noise. The docs are sparse on this setting, so could you elaborate on what exactly the radius setting is doing? Should I just set it low and forget it, or should I keep raising it until the noise begins to creep back in?

thanks!

[joconnell]

There's something very odd there - you're seeing per pixel noise / grain in your global illumination element there and when you use irradiance mapping and light cache any issues in the GI are likely to be large splotches or just general soft blurriness / lack of accuracy. You've got per pixel grain / noise in your global illumination element there and neither light cache or irmap calculate per pixel (unless you use progressive path tracing on your light cache) - are you using detail enhancement in the irradiance map? This is per pixel and you'd have to play with your subdivs mult control for that to clean up the grain you're seeing.

[svetlozar.draganov]

Or perhaps using VrayDirtMap ?
Can you show us RawGlobalIllumination Element?

[leejk]

It was the ambient occlusion settings... see my edits above and questions about the radius setting.

[joconnell]

So that's pretty much the same as any other AO / vray dirt setting. For each pixel in the render, it'll search for other polygons within the raduis value you specify. A larger radius means that more of the scene will be taken into account for the ao (slow) and if you've got more of the scene taken into account there'll probably be more geometry and to capture this geometry accurately enough so that you don't get noise, you'll need to up your subdivs / samples. It's maybe hard to tell you what radius value you should use for your scene since it's totally dependent on the size you made it at but one way of telling is if you've got some really fine detail in your geometry (lets say the thin channel around the wall panel just at the top of your red render region in your example image above) it might be so small that the irradiance map gives you slightly blotchy results there or doesn't give you sharp enough detail. What you can do is make a sphere object in this channel and see what the radius of your sphere is in units - if you make the radius big enough that the sphere goes from the back of the channel to the lip flush with the wall, then this is a good idea what your radius in the detail enhancement / ambient occlusion needs to be. The higher the radius, the more the ambient occlusion effect will spread out (that's just a "look" choice really) but the more samples it'll need to smooth out.

Bear in mind, anything done per pixel will be recalculated per frame so you'll have to make sure your subdivs on it are high enough so that you don't get any fizzing grain on your GI element over the course of an animation.

[alexworx]

Thanks! Really great info.

[Neilg]

I've had so many issues using the ambient occlusion in the GI, it's not worth it. render out a separate pass of vray dirt in a copy of the scene and comp it later, you'll save so much time.

[RockinAkin]

Seconded. Unless you're REAAALLY need to do everything in-render, it's much better to have AO as it's own pass to control in post.

[Morne]

Akin, based JUST on your calculator and not actually seeing the render, is there any kind of "average" assumptions we can make with the figures. For example, looking just at the figures we should be able to tell if it will produce a good image or not.
With that in mind, what should be our goal here?
Should we keep an eye on the min/max image samples or can we just look at the min/max of the DMC Per Pixel?

If we're looking at the DMC per pixel, should the min/max be as far apart as possible, or as close as possible? Also, what would be a good figure here for the MAX DMC Per Pixel Samples (Specifically for ArchViz animation)