I'm rendering a product model on a cyc and the client is going to want the background to change (just a solid color), so I would like to be able to isolate the cyc's reflections so I can just tint those in comp and easily accommodate any color changes. How can this be done? Is there something like the LPE tag for objects, to break out their individual contributions?

On a possibly-related note: this product is a transparent bottle holding an almost-transparent liquid, but the alpha (even with the cyc set to phantom or turned off) is 100% opaque. How can I get the alpha to match the theoretical transparency of the object(s) so I can change backgrounds freely (notwithstanding reflection/lighting changes)? I even tried lowering the bottle's IOR to 1.5 and turning off the environment light, neither of which helped.

Thanks!

1. Yes, you can assign LPE tag to your object and then filter just for reflections hitting objects with that tag

2. You can try filtering for refractive paths ending with B event which stands for background, to get something like Alpha for areas that hit nothing

Both are described here
https://www.sidefx.com/docs/houdini/render/lpe.html [www.sidefx.com]