Renderspeed on AO pass

[Art48]

How do you guys handle the new automatic subdivs?
I render AO passes quite often, meaning switch off all lights, override materials on all objects etc, to make it render fast.

What I noticed is that due to the new automatic subdivs, the rendering takes quite a bit longer than I am used to it for such a simple scene (and I am not talking huge AO radii).
How would I go about increasing the speed for that simple image? I want to keep the crisp image edges from proper AA, but the AO itself can be noise, it doesn't matter too much to me.

Would I increase the DMC noise threshold? Turn on local subdivs? Lower min shading rate to 1? A combination? What is the best way to go?

Edit:
I also just noticed it takes a large amount of time in pure white areas, where the AO doesn't even happen - and it's not displaced or otherwise complex geometry. And the SampleRate pass is blue there, too.

[kosso_olli]

Why not rendering the AO together with the beauty pass? Make an ExtraTex renderelement and stick a VrayDirt in there. The AO will render together with the beauty and nearly no extra cost.

[Art48]

Why not rendering the AO together with the beauty pass? Make an ExtraTex renderelement and stick a VrayDirt in there. The AO will render together with the beauty and nearly no extra cost.

1) Nearly no extra cost?! That would be news to me, since AO needs extra sampling.
2) We sometimes render huge images and memory for AOVs becomes an issue. That and 1) is the reason why I render them separately often.

[Pixelcon]

1) Nearly no extra cost?! That would be news to me, since AO needs extra sampling.
2) We sometimes render huge images and memory for AOVs becomes an issue. That and 1) is the reason why I render them separately often.

Make sure you turn off 'consider for anti-aliasing' in the extratex element and it shouldn't add much, if any render time to your normal render.

[Art48]

Make sure you turn off 'consider for anti-aliasing' in the extratex element and it shouldn't add much, if any render time to your normal render.

I'll try that but shouldn't AA generally not calculate this effect at all since its a shader effect?

Edit: Just tried that checkbox, and (maybe of course?) it ain't working when using my approach of setting everything to black, render without lights etc since I get 100% jaggy edges, like 1 sample edges since the image is basically black and the AA doesnt' consider AO, so it only considers whats visible and that is nothing - also completely blue SampleRate pass as expected. Also the rendering isn't really that much faster.

Even if it works the way you described not adding rendertimes it still is a burden on VFB memory. I know I can skip the VFB and render to an image file directly but I generally try to avoid that.

[kosso_olli]

Memory is really cheap these days. We render images in print resolution of up to 14k and never had any issues with memory and around 20 render elements on our 64gb machines. Just try to render the ExtraTex with the beauty, it makes things much easier. Why render twice if it can all be done together with the beauty pass? I mean, you don't do the same for every single render mask, do you?
With this approach you will get really nice and clean AO. Attached you can find a 100% crop, looks clean to me.

[Art48]

Yeah, we also got 64GB machines but sometimes, especially with displacement, we hit a ceiling. Granted I tend to maximize RAM usage generally, because of the general tradeoff of speed and RAM. I mean yeah I could propably squeeze it in but in my opinion it does indeed really add rendertimes. I'll have to check that but for me it is just extra sampling which equates in extra rendering time. Also usually you don't need the AO in the same resolution as the final image. Mostly half the size is decent enough.

When I got time I will check how much render time it actually adds on some scenes...

[Art48]

Turns out my script which set up the AO AOVs for me was using too high subdivs and since VRay 3 apparently does not treat those subdivs as the ones that get calculated automatically it took too long to render. Dialed down the subdivs and it worked fine.

[Dariusz Makowski (Dadal)]

Ya all can fit ur scenes in 64 gb u so lucky I ported car in scene the other day hit render and ram went to 55gb on a single pass... damn dem heavy data...

[Art48]

Keep in mind you can set all geometry to "Dynamic" instead of "Static" and also check the "Conserve Memory" checkbox. It helps.

Edit: Also you can render directly into a VRIMG without the VFB open. This especially helps when rendering huge images. Drawback is you cannot see the actual image until it's finished (Well maybe you can preview it via commandline tools from the VRIMG file inbetween.)