Mask object innside another object?

[stir]

Hi, this might be a tricky one.

But is it possible to render out a mask for an object innside another refractive object?
In my example i have a model that is refractive and with sss simulating the look of jello.

Then i have a couple of fishes swimming innside it.
The fish is both getting affected by the IOR of the jello and is reflected innside it.
Is it still possible to render out a mask of the fishes and its reflection for color correction in post?
Or if not a mask, is it possible to render out the fishes alone, but still affected by the IOR?

As i write this i understand that this sounds crazy, but i'll ask anyway hehe

Thanks
-Mats

[DartFrog]

Sort of. You can keep your clearish object as-is, but the thing inside should be made into an emissive material. You may want to adjust your light settings so it doesn't actually emit and bounce light around. Turn off all lights in your scene except that one that's inside the jelly. You end up with a black and white mask.