Atmosphere question

[dhavalmistry]

I am trying to render clouds along with god rays and since I will be taking the clouds and the rays to a compositing program, I want do not want to render the atmosphere (so that I can get the alpha channel of the clouds). I turn off "render primary" under the atmosphere tab but that disables the godrays (obviously). Is there a way to keep the god rays and also get the alpha channel of the clouds?

BTW I am rendering an animation sequence.

Any help will be appreciated!

[Tangled-Universe]

The god rays are not elements of the clouds, but of the atmosphere. Clouds cast shadows into the atmosphere and god rays are a product of that.
So you need to output your atmosphere.

I have to think what you'd need to do to get this outputted some way, but quickly I can't think of a way. As far as I know there's no alpha for atmosphere like an alpha for clouds.
I'm also not sure if the future update will let you do so, don't know by heart, nor am I sure if I'm admitted to say so. So I'll let that over to one of the guys of PS.
If something gets to me I'll reply here again.

[FlynnAD]

What about turning off the primary (or perhaps the secondary) visibility of the cloud node (not the atmosphere).

What I would think is that if you can hide the clouds from the camera but still have them visible in the scene, then they should still cast the godrays, if what TU said is true about the godrays being part of the atmosphere (and with the atmosphere still on and visible to the camera).

Didn't try this myself though.

[dhavalmistry]

What about turning off the primary (or perhaps the secondary) visibility of the cloud node (not the atmosphere).

What I would think is that if you can hide the clouds from the camera but still have them visible in the scene, then they should still cast the godrays, if what TU said is true about the godrays being part of the atmosphere (and with the atmosphere still on and visible to the camera).

Didn't try this myself though.

right, but I dont want to render the atmosphere and also want god rays!

[FlynnAD]

This may be a pain in the butt, but

1) what about rendering the clouds separately (atmosphere primary off) to get them separately (you don't actually need the alpha channel then, it'd pretty much be redundant);
2) rendering the sky without godrays and without clouds to just get the color
3) rendering the sky with godrays and without seeing the clouds (primary or secondary off) so that you get a rendering of the sky and the godrays.

Then try compositing the sky-godrays image minus the sky-image (use some type of key difference or subtract channel to try to separate the godrays if you need them separated),
then add the clouds in as their separate layer. Then hopefully you've got your clouds and godrays and no atmosphere.

Perhaps it'll give you what you want??

[Oshyan]

I don't really even understand what an atmosphere "alpha" would be other than just a separate atmosphere pass. The god rays are not a "thing", they are a difference in lighting in the atmosphere due to shadows being cast. I suppose perhaps in that sense you could say it would be a separate shadow pass for the atmosphere? That might make some sense.

Anyway, like others, I can't think of an easy, immediate way to do this, but we may have something that would help in a later release that will have "render layers" (e.g. depth pass, etc.). I know that doesn't address your immediate issue though, I wish I could help more.

- Oshyan

[JimB]

right, but I dont want to render the atmosphere and also want god rays!

Switch off GI and the Enviro Light, make your cloud colour completely black.

If you want to hide or mute the atmosphere above the clouds from punching through:
*Add a new cloud layer (B).
*Unplug B's fractal density shader.
*Make B's density very, very dense (100, e.g.).
*Put B's altitude above the cloud layer you want the god rays to come through (A), and change cloud depth to, say, 100, or whatever means the bottom won't poke through A.
*Alternatively, set B's altitude so it sits within A.
*Switch off B's Primary Rays.

Switch off the sun's visible disc and decide for yourself if you want 'Glow in atmosphere' switched on.

You don't have to switch off GI and Enviro Light, by the way. For a more amorphous look, switch off Cloud Layer A's primary rays, too.

Comp on top of your pass.