How to reflect\catch light but be invisible on render? I want a mash was able to catch light but was invisible on render. I want this effect to happen, but the plane was invisible. Is it possible? Or can I cast colored shadow? I need this in cycles. This question is not about "how to make an obect invisible" it's about how to make in catch light.


Fore example



I need this happen



How can I get light accents without white face??? Do you see that light distributes unequally on shaped objects, how can I get only light fingerprint on transparent background?
I couldn't manage to make this "light catcher" using nodes but as a workaround or just alternate method you can use Baking. For this answer I'm using Blender 2.80 Beta and Cycles but the workflow is the same as in 2.79b.

Scene setup for baking




Background needs to be black.
Light should be fully white - you can change color of it after bake.
Object may be simple Diffuse - needs to be UV Unwrapped.


Baking



Bake Type - Diffuse with Influence Direct.

You should get a map like this:



Using it



Now you can use baked map as a mask to combine Transparent shader with another of your likeness. Color Ramp is for fine tuning mask strength.