Optimize a HDRI(studio's type) scene.

[FrenchLedger]

Hello everyone !

I got a 3ds Max 2017 scene of horology's product to animate (animation is already made and works fine). I'd like to render each frames (869 of them) in 8K and then downgrade in post at 4K. Actually, It's just a fantasy because of the render times.

In 8K it takes more than 10 hours to have a below 6% noise level, I already changed a few things (mostly in mtls) and it now render in a little bit more than 6 hours.
In 4K it's a little bit less than 1 hours now. It's not that bad, but I'm sure it can be better. And I take every second per frame I can save.

My scene is illuminated by a .exr I made with HDRLightStudio. it's a 10000x5000px files with no colors (only blacks, whites and grays) in a CoronaBitmap. Actually, blur is at 0.01. I don't know if it may be an issue. They're no additionnal lights in the scene.

The cameras are Physical Cameras with an aperture of 8.0

The 3d model count 27 720 822 polygons. It's the less I can have without touching the quality of the parts (imported from Solidworks and Alias.

I'm actually out of ideas to make the hour's counts down. I so ask you, do you have any clues ?

Artisticly
PS: sorry for the (maybe) bad english, I'm french after all.

[Njen]

Use a small HDRI to light the scene. Resize it down to something like 1024x512. The renderer won't have to work as hard to sample all of the extra pixels in the smaller HDRI, which will result in faster rendertimes. Also, leave the blur at 1.0, as increased variance in the HDRI will increase rendertimes.

[FrenchLedger]

Thanks for your answer @Njen
I saved a small HDRI, changed the blur value as you mentioned and I ran a test in 720p.

Before : Scene parsing : 22s / Geometry : 7s / UHD Cache Precomp : 9s / Rendering : 13m 27s / Denoising 15s = total: 14 min 22 sec
After : Scene parsing : 25s / Geometry : 10s / UHD Cache Precomp : 9s / Rendering : 13m 2s / Denoising 14s = total: 14 min 02 sec

In a previous step, I unchecked unused maps in the materials. Before that I was at 13 min 10 in the same resolution.
After undo that and the change of all the bitmaps blurs : Scene parsing : 21s / Geometry : 11s / UHD Cache Precomp : 8s / Rendering : 12m 30s / Denoising 14s = total: 13 min 27 sec

I deactivated the denoising (to me 6% noise is fine and it add a patina I like as long as it's locked noise).
Scene parsing : 21s / Geometry : 12s / UHD Cache Precomp : 9s / Rendering : 13m 00s / Denoising 0s(obviously) = total: 13 min 44 sec [I'm sure it's because it's a 1 run not a multiple images median]
Scene parsing : 27s / Geometry : 12s / UHD Cache Precomp : 9s / Rendering : 12m 40s = total: 13 min 29 sec [Okay, that's strange and not so stable]
I killed some unused process on my computer and relaunched a new run and then : it's magic !
Scene parsing : 24s / Geometry : 17s / UHD Cache Precomp : 6s / Rendering : 9m 54s = total: 10 min 43 sec

What about 4K ?
Scene parsing : 24s / Geometry : 23s / UHD Cache Precomp : 7s / Rendering : 56m 40s = total: 57 min 35 sec > yes! almost 11 minutes saved. May we get more ?
{for the record, Saturday I had these values : Scene parsing : 33s / Geometry : 20s / UHD Cache Precomp : 8s / Rendering : 1h 5m 14s / Denoising 1m 49s = total: 1h 8 min 5 sec}

EDIT: I did a run at 8K during the night and I'm impressed !
Scene parsing : 25s / Geometry : 26s / UHD Cache Precomp : 7s / Rendering : 3h 36m 30s = total: 3h 37 min 28 sec > the last time I did a try at 8k it didn't finished within 10 hours.

The 2 next improvement possibilities I'm asking myself on are :
- the image filter parameters (which type ? My width is at 1.5px and my highlight clamping is at 0, what will append if I change them? And if I check the "Use high quality filtering" ?)
- and the type of bitmaps (should I use the standard one or the corona one as I read this in an other forum on a previous old topic? Can I mix them ?).