Precalced GI takes longer to render image?

[japetus]

I've been using the GI precalcing method of Animation (Prepass) and LC on an animation with a flythrough and moving objects. It's working pretty well except it seems like my frames take waaaay longer (like 2 to 3 times longer). I noticed in the vray tutorial here (http://help.chaosgroup.com/vray/help...ials_anim2.htm) that they recommend turning OFF the LC after it is calculated, which doesn't make sense. This also makes my frames take even longer in addition to the 2 to 3 times above. What is causing the extreme time increase? It's basically negating the time spent precalcing and almost isn't worth it except that I'd otherwise get flickering.

[Dariusz Makowski (Dadal)]

Heya

Thats interesting. What are you rendering? Arch/grass/moving objects what is it. Do you use any interpolation in materials?

[japetus]

The materials are pretty simple. Most of them are just flat vray materials with a color of some sort. Some VRay Light materials also but they are not direct lighting, but there are about 450 lights, lighting a series of buildings and objects so maybe it's something to do with them?

[Dariusz Makowski (Dadal)]

Yea its probably the lights... 450 is a high-ich number. How many samples per each light? Can you supply image of scene so I can have a look roughly whats happening? Also settings screenshot would be great too.

[joconnell]

Had you got "use light cache for glossy materials" turned on? It'd accelerate your glossies a lot.

[japetus]

I cannot provide the scene, it's an ongoing project for a client, but I can give you some details on the settings. They're not that crazy... The lights are using the default samples of 8, no motion blur or DOF, adapdive subd of 1 and 2, 1920x1080. The settings tab are vray default, and I have about 15 render elements. Oh, and there are also 6 or so XRefs in the scene.

[Dariusz Makowski (Dadal)]

What about anty aliasing?

Light samples... uhh they should be at at least 24-48 to have minimum optimum impact on scene. Other wise you are wasting time on using AA filter to clean up the noise... - which takes longer to render.

Can do a test for me and disable all render layers + set gray material to everything. See how long that would take to render.

Thanks, bye.

[japetus]

Well the important part here is why my precalculated light takes longer to render per frame than calculating it on every frame. Like I said above, I'm using Adaptive SubD at 1 and 2, the bare minimum for good quality. I skipped using adaptive DMC because yes you are right, it took a long time to clean up the noise. With Adaptive SubD it's pretty noise free. The problem I'm trying to solve is the very long precalculated light render.

[Dariusz Makowski (Dadal)]

Do you have any moving objects? I think unless you can provide scene to support@chaosgroup.com and ask them for 1on1 guidance it will be hard to suggest something... No idea why its taking so long. Could be many reasons user or program bug.

[eyepiz]

It's depends of how long your animation is...Try keeping your scenes as short as possible and your prepass wont be as long. The final renderings usually takes 2 to 3 times longer to render with a 2 frame blend. If you scene isn't too busy you can get away with a 1 frame blend and your render times will decrease a bit.

I've been using the GI precalcing method of Animation (Prepass) and LC on an animation with a flythrough and moving objects. It's working pretty well except it seems like my frames take waaaay longer (like 2 to 3 times longer). I noticed in the vray tutorial here (http://help.chaosgroup.com/vray/help...ials_anim2.htm) that they recommend turning OFF the LC after it is calculated, which doesn't make sense. This also makes my frames take even longer in addition to the 2 to 3 times above. What is causing the extreme time increase? It's basically negating the time spent precalcing and almost isn't worth it except that I'd otherwise get flickering.

[japetus]

It's depends of how long your animation is...Try keeping your scenes as short as possible and your prepass wont be as long. The final renderings usually takes 2 to 3 times longer to render with a 2 frame blend. If you scene isn't too busy you can get away with a 1 frame blend and your render times will decrease a bit.

Thanks eyepiz, that's what I was after. So it's the blending huh, interesting. That's too bad the frame blend adds so much render time. Something to keep in mind next time I guess!

[LarsSonparsson]

If you use saved IR, you can turn lc off when rendering. All the data from lc is saved in Ir map, so it's not needed anymore. Only needed, if you want to use lc for glossy rays.

You should also turn the core limit (number of passes) from 8 to 0. That way lc calculation uses all cpu power automaticaly.

[japetus]

If you use saved IR, you can turn lc off when rendering. All the data from lc is saved in Ir map, so it's not needed anymore. Only needed, if you want to use lc for glossy rays.

You should also turn the core limit (number of passes) from 8 to 0. That way lc calculation uses all cpu power automaticaly.

I noticed in the tutorial that they say to turn LC off, but in my experience with this project, my render times doubled again and I couldn't afford the hit, so I left LC on. It's great to not have flickery GI with this method but it really needs some speeding up. I'm going to avoid using it again unless I can find a way around taking a 3x render time hit...

[tammo]

I came to the same conclusion.
With animated geometry its usually faster to render with single frame gi and get rid of the flicker by shooting a lot of hemispheric rays
than using a precalculated blended mode.

Turning off the secondary lightcache GI maybe slower because vray cant use interpolated glossies anymore?

[eyepiz]

Interesting...never tied that, how do you shoot hemispheric rays in you scene?

I came to the same conclusion.
With animated geometry its usually faster to render with single frame gi and get rid of the flicker by shooting a lot of hemispheric rays
than using a precalculated blended mode.

Turning off the secondary lightcache GI maybe slower because vray cant use interpolated glossies anymore?