grain in cloud

[Dune]

I'm trying to get the last grain out of the sky, but it doesn't seem to work without greatly increasing render time.
Upping AA from 5 to 6 increased render time to 150%, but grain was as much.
Upping cloud quality from 0.35 to 0.6 added 40% to render time, but grain was as much.
Upping atmo quality from 16 to 24 didn't do anything either, but upped render time 50% as well.
It's only some darker areas near the sun that show grain, so it's not too bad to blur in post (or just leave it), but I want to know nonetheless. Any advice?

[kaedorg]

I don't want to scare you about render time but here are my settings for clouds :

AA : 8
Cloud quality : 1
Atmo quality : 64

Of course, render time is huge. Last render for a 6000 x 1800 was 160 hours

As i am lucky to have 3 rendering PC and not in a hurry, that's fine for me and result has no grain.

I think that you can't afford such kind of render time for these grains. I would go to post.
As I didn't try to see which setting is the more efficient about grain, i can't say which one has to be up in priority.

David

[Dune]

I'm terrified now    That's awfully long.
That's the problem, I don't want these huge render times. Last calculation showed that with detail 0.5  AA5 and atmo samples 16, cloud Quality around 0.4 one whole render of 9600x6000px will take 16 hours. I (we  ) need to do 14 of those. So I try to keep it a bit low, but with quality that's just good enough. At a certain point it won't matter much how much you increase quality, and I want to find that point.

[Tangled-Universe]

Well, how do I say....a voice in the wildnerness of me saying to don't use RTA?

Matt recently stated, and he's right of course, that using RTA gives you predictable results.
This is logical, since AA4 gives you max 16 samples per pixel to apply AA on and that results in a certain noise level.
So as long as you don't severely undersample you will always end up with a similar result when using AA.

But when do you undersample???

It's a big problem to assess how much cloud quality you need vs. AA samples. You just don't know.
So let's have a look at another part of the render process which also has AA as determining factor for final quality: objects/populations.
There we often use AA8 or sometimes even a bit more to get smooth result with low noise.
Go to your pixel sampler settings in your render node and increase AA.
See how the samples increase and the noise threshold lowers?
That noise threshold is the difference in luminence between adjacent pixels that AA setting is aiming for.
So the lower number = the smoother the results.

Now you want smooth and clean clouds and thus you need quite a few AA samples, but also not too few atmo/cloud samples to start with.
If we don't have enough of samples set in our atmo/cloud then we can even use AA16 and still have grain.
The lack of samples causes so much noise that AA just can't get the job done.

Now you may think: ah that's easy...I just stick to AA4 or AA6, turn on adaptive sampling and give it enough atmo/cloud samples to work with.
Well...no.
You can also give too many samples which means that for every adaptive AA stage it needs to chew on all those samples to then find out the threshold level for luminance is not met and then continues to the next level of AA.
It can sometimes even be slower than undersampling!

Matt changed the cloud samples settings to quality only recently to avoid the discussion: I use 256 samples and my cloud is noisy...
To then later read that the cloud depth is 1000 with density and sharpness of 5.
Now the relation between those 3 factors are tied in the quality setting of the clouds.
A HUGE improvement in that regard.

Since we don't have anything similar for RTA I can make a long story made short. Don't use it.
Unless you know exactly how AA interacts with the atmo/cloud settings.
You need to reinvent this for every scene.

[Dune]

Thanks Martin. Ì take it that you mean not using defer atmo/cloud? I could try that, see what happens. My clouds are rather normal, max height is 500m, max sharpness is 5, max density 0.05. Nothing special.

[Tangled-Universe]

Ghehe, yes
(did I say somewhere you should? I can't see where quickly)

Try it and see which one you find working best.
I just tried to explain why I often don't use it and generally advice against using it.
I do use it though, but quite rarely.

[RArcher]

I assume you are exporting this out in render layers Ulco?  If so, you could easily go with the lower quality / faster render times and then simply do a little noise/grain reduction/smoothing on the cloud layers in whatever software you use to put the image back together.  Getting it perfect in the renderer is a great goal, but not when it takes so much longer.

[Oshyan]

Ulco, can you post an example image of the issue you're seeing? Definitely test with Defer Atmosphere off, though if it's a noise issue I really don't know why Martin expects it to be *better* with Defer off. You already increased values fairly high and if it apparently had no effect, it's likely to *not* be a straight sampling issue IMO.

Danny, aside from some sampling changes in the *atmosphere* that we mentioned in the TG 3.1 presentation (not in clouds, as far as I'm aware), there should be no difference between TG2 and 3 with raytrace/defer atmosphere. More compellingly, the sampling changes would affect non-defer as well. We'd really appreciate if you could do verified, exact-same-scene, side-by-side tests to demonstrate this problem you're seeing.

Discussion on raytrace atmosphere render time differences split out to here: http://www.planetside.co.uk/forums/index.php/topic,17706

- Oshyan

[DannyG]

Agreed they are high settings, however the times are relative to lower sample values.

[Dune]

I'm doing a (large) crop of a 9975x6000px render now, with defer clouds off, see what it will look like (3 hrs busy now). I'll later do some smaller crops and test the difference.

[Dune]

Difference between defer off and on. Huge! Same detail setttings though, so it might be better with higher cloud detail and defer off. Still have to check that. It does cost time, as the defer off took 6 minutes, defer on took 19 minutes for this crop.

[Tangled-Universe]

So what were the settings? (both atmo and cloud)

[Dune]

cloud quality 0.4 atmo 16, so fairly default. Fatter cloud height 500m, density 0.05. Atmo not changed from default. Perhaps if I up cloud quality to 1 and do no RTA/defer, it might work out quicker and without grain. Have to check still.
I decreased cloud coverage for the final renders by the way, finding it too heavily clouded.

[Tangled-Universe]

cloud quality 0.4 atmo 16, so fairly default. Fatter cloud height 500m, density 0.05. Atmo not changed from default. Perhaps if I up cloud quality to 1 and do no RTA/defer, it might work out quicker and without grain. Have to check still.
I decreased cloud coverage for the final renders by the way, finding it too heavily clouded.

Ok that doesn't help much
What was the AA?
What was the cloud quality?

For example, any AA greater than 4 with 16 atmo samples takes very long.
Atmo samples are the most expensive with RTA.

The best way to test differences is on a more representative part of the scene, including objects and such.
You can optimize your atmosphere/cloud rendering with RTA and then very likely find out that it doesn't work for your project, since objects/populations look rather ugly with AA4.

Or I can repeat my general advice: leave RTA alone

[Dune]

You're cryptic  What doesn't help much, the settings I gave you? AA was 5, detail 0.5. Cloud Quality 0.4 as said in last post.

And your general advice; leave RTA alone  You mean no defer atmo? That's what giving me the grain!