Rendering a transparent sky

[dorianvan]

I need to change out my TG sky for a timelapse sky and composite in After Effects (wish I knew how to do nice timelapse skies in TG). Anyway, in Max/Vray, I can render a scene with a solid black background and a nice environment for GI; the black background gets rid of the object/terrain halos and I can save out an image with transparency for comping. Is there a way to render the sky transparent AND render the image so as to not have halo artifacts when comping?

[RArcher]

Render Elements with TG3 are what you are looking for.

http://www.planetside.co.uk/wiki/index.php?title=Render_Layers_and_Render_Elements

[Matt]

You can also render with a black background, just as you did in Max/V-Ray, by unchecking "Visible atmosphere" on the Render node (or on the Render Layer). Combined with the alpha element which can be output as Render Element (see the link Ryan posted) you'll be able to comp your terrain over another background without any halos.

With the Render Layer settings you can go even further than that. If you want some atmosphere to cover the distant terrain but not appear over the background, you can uncheck "Atmo/cloud on background" on the Layer Settings tab of the Render Layer.

Matt

[Oshyan]

Or, if you want to keep it all Terragen (better integration), you can animate the sky in a time-lapse style way. You can get started by using a Translation node on the noise shader for the cloud. Try translating in X or Z (horizontal movement), and then more slowly in Y. The new 4D noise in Terragen 3 can also work well here, but is not as easy to explicitly control.

- Oshyan

[dorianvan]

@Ryan, thanks. I need to do some testing with the Alpha and other elements more now. I have tried the Surface Depth element, but had to crank up the levels in PS to get the depth to show up; it worked though.
@Matt, whether I unchecked Allow atmo/cloud to be visible or not (while I had Atmo/cloud visible (Render Settings) unchecked), the atmosphere appeared to be there on the terrain, albeit only about half as "thick" as with Atom/cloud visible enabled. The only thing that removed it was reducing the clipping distances or turning off Enviro light. I am running the latest TG3, so not sure if it's a bug or I'm doing something wrong.
@Oshyan, I'll definitely try some animation tests, maybe even the vortex shader if I can figure it out.

[Matt]

@Matt, whether I unchecked Allow atmo/cloud to be visible or not (while I had Atmo/cloud visible (Render Settings) unchecked), the atmosphere appeared to be there on the terrain, albeit only about half as "thick" as with Atom/cloud visible enabled. The only thing that removed it was reducing the clipping distances or turning off Enviro light. I am running the latest TG3, so not sure if it's a bug or I'm doing something wrong.

It sounds like you're seeing GI then, not atmosphere, but I don't know for sure. I could say with more confidence if you can show me a render.

Matt

[dorianvan]

Hi Matt. The cloud shadows are there on the bottom 2 images, but I don't see much of a difference between the two.

[Matt]

It looks reasonable to me. I don't see any atmosphere on the terrain. What are you trying to achieve? If you want your cloud shadows to be black then that requires turning off GI (which you can do globally or per render layer). Or no cloud shadows at all? If so, I think you'll need to disable your clouds. There are ways to stop clouds casting shadows but all of them will change the lighting in some way.

Matt

[dorianvan]

Thanks Matt, I wasn't trying to do anything in particular, you mentioned turning off atmo/cloud on background, so I just wanted to see the difference between off/on (on the bottom 2 images); and I don't see any difference. But maybe it just depends on the scene that is set up though.

[Matt]

Thanks Matt, I wasn't trying to do anything in particular, you mentioned turning off atmo/cloud on background, so I just wanted to see the difference between off/on (on the bottom 2 images); and I don't see any difference. But maybe it just depends on the scene that is set up though.

I missed your reply until now. The "background" is the background sphere, or in other words the "sky", and any other objects with an alpha value of 0. The reason there is no difference in the bottom 2 renders is because in both renders you've already disabled the visible atmosphere globally, so there isn't anything to be made visible on the background. To see what difference "Atmo/cloud on background" makes you need to leave "Allow atmo/cloud to be visible" ON.

Matt