Need to render a mask that is behind glass

[RobH2]

I have an object behind glass. I need to render a mask of it. The transparent material obscures the mask and if I render the mask with the glass turned off, the mask is not in the correct location due to refraction.

How can it pull a mask from something behind glass while leaving the glass enabled?

[Frood]

Currently you can't. Simply that. Vote for

"Refraction/Reflection working with masking render elements (CMasking_Mask,CTexmap, etc...)"

here:

https://forum.corona-renderer.com/index.php?topic=96.0

if you need it desperately.


Good Luck

[RobH2]

Good enough. I'll vote.

Well, we all think that everything we need is "desperate" don't we...lol...? I'll render the mask in VRay I guess. I think it can do it.

Thanks for the fast response.

[iancamarillo]

or hide the glass and re render only masks. I dreaded this workflow but surprisingly was very fast for an animation I did

[Frood]

You don't get a refractive mask doing so. Depending on the (glass) object you only get some approximation but usually just a wrong mask.


Good Luck

[iancamarillo]

yes sorry, I misread the initial post

[pokoy]

Smartass alert here but can't you disable all lights, set the glass reflection to zero, set the object that you need a mask of to self illumination 1/white and render that? Not a direct solution but maybe a viable workaround.

[Frood]

Interesting hack! Now we have shadowcatcher workaround for opacity masks and self illu for refraction - and a horrible workflow :) But for that one mask quickly needed, why not.


Good Luck

[pokoy]

Yeah it's not very elegant but will probably work, I've used this setup on a few occasions. Forgot to specify that you'd probably need to use a LightMtl because you need to make the object not emit any light.

If you need the mask for reflections too you need to keep reflections enabled for the glass material. 

[iancamarillo]

nice!

[actrask]

I just had to do a similar trick that pokoy used. Put a Rayswitcher on the object behind the glass and have only the 'refract override' set to a self illuminated RG or B color. This will stop the self-illum from kicking out any GI. Put a flat black material on everything except the glass and refracted object. I'd save a scene state before doing this.

Aside from all that, is it really that hard to implement this or is it just not a high priority?

[julienbe]

Same problem for me here.
I'm working on a commercial with a fish in an aquarium. It is practically impossible to use the render elements for post-production because of the refraction of the aquarium glass.

JULIEN

[actrask]

What if you set the aquarium glass object to "not visible to camera"?

[bluesarchitecture]

i found this...

dont know if it helps.

https://coronarenderer.freshdesk.com/support/solutions/articles/5000529357-how-to-make-an-object-invisible-in-masks-render-elements-

[actrask]

Wow, I never knew about that. Thank you!