How to add fake reflection to live action plate window?

[Yngvai]

I'm working on a shot where a CG Optimus Prime drives up. One thing that would really enhance the realism of the shot would be to add Optimus's reflection to the windows in the building on the live action plate.



Is it possible to do this? I would need to composite the reflection of just Optimus but still allow the background plate to show...like an alpha channel reflection. Creating small planes of glass material in 3d space in the approximate location obviously doesn't work because there's nothing behind the glass in the virtual 3d space.

I did some searches of the web but couldn't find any solutions relevant to this problem.

I'm using Blender with Octane Render.

[SSmolak]

This probably can be done inside Octane using AOV mixing with layers and custom AOV as mask.

[Yngvai]

Thanks for the response. Looks like I won't need to do the reflections anyway. I had some other footage where a delivery truck drove by while filming, and when the truck is in the approximate location of Optimus, no reflection shows up in the windows.



To confirm, I created a specular reflective wall and turned off the HDRI environment so that the wall would only reflect sunlight and Optimus. Optimus's reflection on the wall is off the screen.



Thus I don't need to worry about the reflection.

That said, it would be awesome if Octane had a reflection catcher option for materials just like a shadow catcher option. Looking back on other OTOY posts related to this topic, I've seen other people request such a feature.

[Hesekiel2517]

It's already possible with the layer system. Here is how to do it: https://www.youtube.com/watch?v=YB4LBf_t_Xs

This works great, but there are still some limitations so I would like to see this improved aswell