Crisp white clouds

[funkfather]

Hi all - first post here.
I have been playing with some of the clipfiles in the clouds section and I want to understand why my images have these weird soft dark patches. Can anyone explain that to me - what causes it and how do I get rid of them.

I want nice white crisp clouds, with no weird smudgy areas.
thanks for the help

[TheBadger]

Nice looking clouds.

The "smudge" almost looks like a second cloud layer. Don't worry though, someone who can help you will come along sooner than later.

[Upon Infinity]

If I had to guess, GI or try fiddling with the 'Glow' values of the cloud layer.

[Matt]

It looks like it's the GI in the clouds. Try turning this off by setting the cloud's "scatter colour" to 0. Doing that will stop the clouds from self-illuminating, and they'll only pick up GI from the rest of the scene (e.g. the sky). If the new clouds are too dark, you might want to bring back the scattering but changing the GI settings on the render node. You could try reducing the "GI blur radius" and/or increase "GI relative detail" - either of those should reduce the size of the patches.

Matt

[funkfather]

Thanks Matt - that seems to be working. I am rendering a version now and will post it tomorrow. Still a couple more tweaks would be good but I like what I am seeing so far!
I ended up turning up cloud colour to 1 and scattering colour down to 0 and underexposing a bit.

[funkfather]

Here is the latest. It is a lot better but still not perfect. Any further ideas?

[Matt]

Is it just one cloud layer? If the scattering colour is at 0 then I wouldn't expect to see the GI glowing in the clouds anymore, but if you have more than one cloud layer they will still cast light onto each other regardless of the scattering colour. If that's the case then you might need to reduce the enviro light contribution on the clouds.

Whenever GI is involved it's a good idea to use real-world values for the cloud brightness. For dense clouds like this you should not go much higher than 0.25 for the colour. The GUI has an indicator to say what albedo a particular cloud colour corresponds to. 0.25 can result in 100% albedo if the clouds are dense enough (due to the way volumetric colours are calibrated in TG), and 100% is the maximum albedo possible in the real world so you don't want to go much higher than this.

What are your GI settings?

Matt

[Tangled-Universe]

Hi Matt

Thanks for the info, well explained.
In my experience clouds get darker when density increases and vice versa.
Consequently I need to tweak cloud (scattering) colour and the propagation/fake scattering settings.
I know it's a matter for tweaking the scatter function curve as you explained to me some time ago somewhere else.

However, also in the light of this topic, how does this actually work?
In my experience it seems there's more to it than only cloud (scatter) colour.
For instance, how does this scatter function curve look and how do they relate to the glow settings and cloud (scatter) colour?
Because whenever I do clouds I always have unwanted burned-out glow 'at the side where the sun is'.
Setting both glow power and amount to 0 still results in burned out parts in the clouds.

Likely there's a recommended density for cumulus clouds, but what is it? Which value represents real world the most.
In my experience something along 0.025 to 0.075 (measured by eyeballing how trees fade into these clouds and check with reference).

I remember you helped someone once with reproducing ice crystals on Mars and there you gave a pretty descriptive step by step on your approach and thoughts throughout the whole process.
Can you do something similar for this? Start with a default cloud layer, set up density shader (I have a couple of good ones) and set up cloud node.
Or the other way around, because the density shader is also important in how the density set in the cloud node really turns out.

Obviously, there seems no end to it

Cheers,
Martin