Extremely Noisy Lights

[Dippndots]

EDIT: I'm an idiot with too many tabs open, can a mod please move this to I Need Help

So I have this weird problem as you can see in the attached image. The sphere lights are really noisy, even though the render thinks it has reached 4% noise.

They are corona sphere lights, visible directly only, and using kelvin settings, no maps or anything else used.

Any ideas?

Edit: this is a top down aerial shot of an exterior garden area, in case you're struggling to figure out what you're looking at :P

[Dippndots]

Looks like the root cause was actually the geometry lighting the inside of the building with a lightMTL and bitmap on them to make it look like a furnished interior.

[Ondra]

so can we close it?

[Dippndots]

I guess so, an object with a bitmap-based lightMTL is always going to be noiser than a plane light right? I guess the best way to do this in future would be a LightMTL that isn't emitting light and have a plane light in front of it actually producing light right?

[Ondra]

yep, it complicates the light transport, so render time increase is expected. I would have to see the specific scene to tell more

[Dippndots]

Ok, this is probably one of the rare instances I can send you a scene, so I'll put it together by the end of the day, no rush for you though.

[Ondra]

ok, upload it to marcin, he can take a look and pre-screen this. I will look at it if it seems like a bug

[Dippndots]

ok, is that via the usual private scene uploader?

I guess the only thing to check is why these interior LightMTL lights are affecting the noise level of lights in another lightmix layer?

[Ondra]

yes, go for the dropbox uploader from my signature

[Dippndots]

ok, thanks

[Dippndots]

Hey Ondra, sorry I haven't sent through the scene, I've been testing all day. I fiiiiiinally have nailed it down.

The noise is caused purely by the HDRI lighting the environment. Strangely, the lower the Output Amount is on the HDRI corona bitmap (or 3ds max or Vray HDRI loader), the more time it takes to render the image and reach my 4% noise limit. I've attached a picture at output amount 1 and .01 and as you can see, the .01 takes significantly longer to render and is much more noise-free than the 1.

If you want, I can try to recreate this in another scene and send it over in the morning.

[Ondra]

this looks like something we are aiming to greatly improve in Corona 1.7 ;)

[Dippndots]

Ok, yes, it looks like we can't render with the HDRI at .01 and then ramp it up using lightmix because the environment lightmix element seems to include influences of the other lights in the scene.

Powering down the lights and adjusting the camera exposure to compensate for the .01 HDRI results in the same behavior as the 1.0 HDRI, which makes sense I guess.

Any ideas on a half-way solution in the meantime? It is prohibiting us from being able to render clean exterior night animations.

[4b4]

I'm using the C4D version so not sure if this is relevant in MAX but I've noticed huge slow downs with high numbers of lights and groups. You might be doing this already but if you're using spheres make sure the render perfect box is checked and drop the segments down to the lowest you can. I've found this massively speeds up scene prep and I think is helping render speed / noise reduction too.

[Dippndots]

Thanks b4b, I believe in Max, corona sphere lights are changed into a special perfect sphere when possible.