please, need some tips for reducing grain

[miohn]

Hi,

as long as I use only HDRI for lightning, everything renders fast
and without any noise/grain (with DL).

But as soon as I add some arealights for highlighting some objects,
I get lots of noise/grain on walls and reflecting objects and I cannot
get rid of that noise.

Tried more max. samples, tried higher sample rate in light settings.
Tried higher glossy- and spec depth but its still grainy around that arealights.
I cannot get too high, because I need to render lots of frames and need
rendertime below 2 minutes.

Any tips whatelse I can try?
Do I miss something with using HDRI and arealights?

thanks much
Mike

[NVN]

scene?

[miohn]

Hi,

cannot send scene or image because its a working project
and scenefile is btw. too large.

Imagine a large hall with walls/panels and metall exibition objects.
About 20 small arealights should highlight the objects in front of that wallpanels.

I have moderate settings (DL, max. samples 300, spec depth 12, glossy depth 32)
which give me very clean renders in about 2 minutes per frame, but only if I
use an HDRI for overall lightning only.
As soon as I activate these 20 arealights, I get this hugh amount of grain in the
surrounding of these arealights.

To get rid of the grain, what I've tested so far, I need about 5.000 max. samples.
But this results in rendertime around 12 minutes for my detailed scene.
3.000 frames x 12 minutes ....... my rendering will be ready for easter.

I cannot understand, why arealights causes so much more grain compared to hdri lightning
and I think, that I'm doing something wrong.

Mike

[aoktar]

Mike do some search for the topic on general forums. There is lot of info about tips for this.

[garytyler]

From my experience, this is where Octane falls a bit short. I recently had a scene similar to this, a roadway with about 20 street lights, and had to just deal with very long render times. Of course, adjusting settings would help but once I found the best settings, there was no magic fix.

Neat Video is pretty good with fixing "even" grain and I found it to be a lifesaver in that situation.

[miohn]

well, a bit grainy renders I also solve with Neatvideo or similar tools.

The problem with the grain mostly happens on large scenes and I'm just
wondering, why there is this big difference between HDRI and arealights
when it comes to noise. And I don't know how to deal correct with the lightsamples.


thanks anyway!

MIke

[aoktar]

Pretty you should use "coherent ratio" for grainy areas. It's a parameter for concentrating the calculation to dark areas. Also use large emission surfaces and big amount of samples in emission textures

[garytyler]

well, a bit grainy renders I also solve with Neatvideo or similar tools.

The problem with the grain mostly happens on large scenes and I'm just
wondering, why there is this big difference between HDRI and arealights
when it comes to noise. And I don't know how to deal correct with the lightsamples.


thanks anyway!

MIke

I saw a tutorial once that gave me a way to deal with light samples that made a lot of sense. I wish I had a link but this is basically how it went:

1. Set all emissions to 1 sample.
2. Set Live View to Clay color setting.
3. Render to Live view. Default 128 samples should be fine but more can't hurt.
4. For all lit areas that show additional grain compared to other lit areas, increase the samples for the emission affecting that area. This will give an even light sample distribution to the entire scene
5. For each camera angle in use, adjusting light samples closer to the camera a bit higher than the others for the render can help by putting more rendering effort towards the most important lights.

Since the samples are actually just a ratio, starting with 1 makes sense. I haven't needed to go above 10-20 for any emission since using this process and it does help a lot. If you had a ton of lights in your scene, and only 1 or two lighting the foreground, I could see needing to go up to 90 or 100.

Maybe aoktar can chime in on this method.

[miohn]

Hi garytyler,

thanks! Seems to be an interesting method I will try asap.
For now, I just killed all arealights and went for hdri only
and compensate lightning inside camera a bit.
So I come to about 1 1/2 minute per 1920x1080 frame without
any noticeable noise.

Ahmet, I've read somewhere a while ago, that "coherent ratio"
only makes sense when using max. samples above 500 or so.
Is that right?

thanks
Mike

[kacperspala]

I do it that way :

Render at 2x resolution with fireflies reduction (octane feature) at full. When you decrease res to normal (divide/2) it will be sharp and noise free.
You can also get a lot lower with sampling rate if you render at double resolution. IE - for 1920 x 1080 i need 3h to render my scene @ 6000 samples. Instead i render 3840 x 2160 @ 3000 samples. Renders faster and after downsizing it has better quality. Also - it gives you much more room for retouching - if there is still noise in your 3840 res image, the photoshop surface blurr/smart blurr will work much better on higher res image.