How to set the alpha channel

Discussions regarding Materials, Material-Compounds or Shaders, etc.
Pancho
Posts: 659
Joined: 19 Sep 2010, 11:28

How to set the alpha channel

Post by Pancho » 16 Mar 2014, 15:23

Well, not so experienced in SI rendering. In LW or Modo I can easily set the alpha value in the material and in the render channels whether I want pre- or unpremultiplied rgbs.

How do I do this in SI (e.g., one object white alpha unpremultiplied, while background black alpha)? Especially in Redshift?

Google spits nothing out, only alphas used for texturing.


Cheers!!!

Pancho
Posts: 659
Joined: 19 Sep 2010, 11:28

Re: How to set the alpha channel

Post by Pancho » 16 Mar 2014, 19:32

No one? Unfortunately I can't find anything on this subject. Do I need to create some funky multi color matte and render the whole stuff twice? The alpha channe would be sufficient for me if I can just isolate my main object.

Unpremultiply with Alpha in Redshift? Anybody? Owei?

angelous4x
Posts: 133
Joined: 06 Nov 2011, 05:24
Location: new York

Re: How to set the alpha channel

Post by angelous4x » 16 Mar 2014, 20:38

not sure havnt played with RS for a while. but if you look into there forms or documents I am sure you could find it.

www.redshfit3d.com

Pancho
Posts: 659
Joined: 19 Sep 2010, 11:28

Re: How to set the alpha channel

Post by Pancho » 16 Mar 2014, 20:46

Nope! Looked twice through it. Either I'm blind or it's not there.

NNois
Posts: 729
Joined: 09 Jun 2009, 20:33

Re: How to set the alpha channel

Post by NNois » 17 Mar 2014, 09:07

hi,

with mental ray
1, there is the opacity shader doing just that ;-), just plug your network into it
2, If it's don't work you can also try driving the "alpha" doing some input/output gymn: out of your shader tree use 3 "picker" each one a channel R, G, then B then combine them in a RGBA combine node, driving then the alpha can do the trick.
3, you can also take the AOV route (aka render channels), take a color 4 passthrough the plug your shader in it. Add a channel the plug a scalar store scalar in channel, drive the opacity here, you won't see anything but you'll have your opacity alpha for your comp ;-)

with arnold, i think you can just drive the opacity parameter but also unchecking the "opaque" switch

don't know for the others

++
Noël