refraction / reflection alpha exclusion of env.

[andrewjohn81]

one of the things that stinks about alpha in vray is reflections and refractions. Alpha will always equal 1.0 unless you only want shadows because it will reflect/refract the environment.

If I have a completely transparent object with an object behind it, I would assume that I would have alpha of 1.0 where the object behind it got refracted as well as probably the edges since those usually will end up refracting the floor or something like that. But pretty much all you'd see is the refracted object in the alpha. This is not the case in Vray though, because it refracts the environment as the same value.

I'd like to be able to turn that off. This is the same for reflections. I want to be able to use an alpha of -1.0 and be able to have alpha for physical reflections Only without alpha for the reflections of the environment.

As far as I know that isn't currently possible, but it should be possible to do.

[vlado]

I'm lost... can you post some sketches of what exactly you need?

Best regards,
Vlado

[andrewjohn81]

Sorry, I can't because they block nearly every image hosting site here.

Basically I want the environment to be ignored in the alpha.
I have an sphere which is 255 white in refraction so it is all trasnparent. Now I only want the reflections. It's really nice when reflections block alpha so you can comp them easier, but I don't want the environment to be included. I only want physical objects.

So in this case, if I have a floor and a white environment I want the floor to be in the alpha, but not the white environment. The bottom of the sphere would be white, or close to white depending on how reflective it is, but the top would be pretty much transparent since there are no objects.

Does that make better sense?

[trixian]

Doesn't the current refraction alpha do exactly that? Can't remember getting my environment map affecting my refraction alpha.
As for reflection alpha, afaik vray does not support this (yet).

[andrewjohn81]

Ah, i'm sorry, you are correct. The refraction settings do work fine the way they are.
Reflections would be nice to have the option to completely ignore the environment though.

I like your (yet) statement. That's what I like to see. Wishful thinking.

[dlparisi]

Reflections would be nice to have the option to completely ignore the environment though.

You can override reflections (and refractions) via the environments rollout.

[andrewjohn81]

yes, I know you can override the environments for those, and even separately, but that's not what we're looking for here.

If you have a transparent object which is reflective it needs to be able to include the reflections for objects in the alpha, but the other reflections (ie. the environment reflections) should not be included.