Clouds Pass Alpha/transparency

[sk8ape]

  I'm new around this part, I been playing with terragen 2 for cloud generation.
I'm not sure if Terragen is capable of doing render buffers, so, I'd like to know if it's possible to render just a cloud pass with an alpha channel, to comp together with a render from Lightwave.

Thanks

[LaFrance]

here here... anybody figured out how to do a holdout shader ? (blocks or "holds out" the color of things behind, but is black in the alpha channel?
also very useful for rendering layers to be composited.

[rcallicotte]

Haven't tried the Holdout Shader.  Is it new?   

[PorcupineFloyd]

After your render is complete check Terragen image temp folder - there's a separate image with an alpha channel of your render (and your colour render also).

[rcallicotte]

Right.  Still need to check out this new shader...

After your render is complete check Terragen image temp folder - there's a separate image with an alpha channel of your render (and your colour render also).

[Oshyan]

There is no "holdout" shader. LaFrance was asking for a way to do this kind of effect, which is common in other apps. Unfortunately we don't have any direct support for this. I'm honestly not sure exactly how it needs to work, so though I imagine there is some kind of workaround, I'm not sure what the best approach would be. The alpha is easy enough to get of course, as others described.

[See my post below -Matt]

- Oshyan

[rcallicotte]

Oh.   

[neuspadrin]

There is no "holdout" shader. LaFrance was asking for a way to do this kind of effect, which is common in other apps. Unfortunately we don't have any direct support for this. I'm honestly not sure exactly how it needs to work, so though I imagine there is some kind of workaround, I'm not sure what the best approach would be. The alpha is easy enough to get of course, as others described.

- Oshyan

.... or you're holding out on us thus the secretive name of the shader!

CONSPIRACY!!!!

[PorcupineFloyd]

There is no "holdout" shader. LaFrance was asking for a way to do this kind of effect, which is common in other apps. Unfortunately we don't have any direct support for this. I'm honestly not sure exactly how it needs to work, so though I imagine there is some kind of workaround, I'm not sure what the best approach would be. The alpha is easy enough to get of course, as others described.

- Oshyan

.... or you're holding out on us thus the secretive name of the shader!

CONSPIRACY!!!!

LOL

Happy Easter, and so on and so on

[Matt]

here here... anybody figured out how to do a holdout shader ? (blocks or "holds out" the color of things behind, but is black in the alpha channel?
also very useful for rendering layers to be composited.

Assign a Constant Shader to your object, and set its colour and alpha values to black. (This is also what the Background sphere uses.)

In Terragen the alpha channel is saved as a separate image with RGB channels to represent different amount of alpha at different wavelengths, but the principle is the same. The alpha images can be found in your temporary files folder (File -> Explore/Reveal Temporary Files). Or if you render using the settings on the Sequence/Output tab in the render node, you can enable "extra output image" there. The Extra output images are just alpha images in current versions.

Matt

[JimB]

In a separate render, switching off Primary Rays for the Atmosphere shader, or even disabling it altogether, will give you a completely black Alpha for the sky all the way to the horizon, but keep the opacity of the clouds as white. If you render using the sequence tab (Render Sequence) and have Extra Output Images switched on, the Alpha will be rendered and saved automatically. Be careful not to overwrite your beauty RGB pass that has the Atmosphere intact, so use a different name for the RGB image. If the Alpha is all you need, you can dispense with raytracing, shadows, GI, etc, for a faster render.

[sk8ape]

Thank you all, with your suggestions and poking around, I got what I needed.
Turning off Surface visible on the quick render or full render panel while leaving Atmosphere visible on, does the trick, just clouds with an alpha in the temp folder.

Thanks!

[bobbystahr]

Good find mate...we really need a Tricks n Tips Forum...this would be an ideal candidate to start it off...another cool EasterEgg.. ...

[Oshyan]

Perfect candidate for the Wiki if you ask me actually. A forum is great for ongoing discussion and figuring out ideas, but a wiki is better for documenting known solutions.

- Oshyan

[bobbystahr]

Right you are...still not used to it being there.. ...