How to create renderelement for object reflected in other object?

[fraggle]

Hello,
I wondering what's the way to create a render element to select object visible in a mirror. Not the mirror itself, but what reflect in the mirror without making another render.

Thanks

[Neilg]

In the mirror material change 'affect channels' to 'all', then give the object in the reflection a channel and it'll be both visible and in the mirror. Give the mirror a different channel if you want to use that as a mask to isolate only the reflected object.

[fraggle]

Great, thanks

[fraggle]

I must probably do something wrong because I can't see the IDobject in the mirror.

[fraggle]

Hello,
Can somebody give me the solution to be able to select an object inside the reflection of another object.
Thanks

[Svetlozar Draganov]

The teapot is probably barely visible in the multimatte render element since it's IOR is very low. MM element takes that into account and creates a mask that corresponds to it.
Here is a quick example following your setup:


If you can't see the reflection matte even with higher IOR values, please attach the scene for investigation.

[fraggle]

Thanks,
i used the same parameters (affect all) but in the refraction slot to get the IDobject behind a glass, but it doesn't works. What's the trick here?

[fraggle]

[fraggle]

Also, let me add that I'm looking for several objectID, so if I override ObjectID by a channel ID I'm going to lost individual selection by object.

[joconnell]

I don't think object ID can work with this, it's an integer channel that can only store whatever object is closest to camera in each pixel. You'll have to use multimatte or cryptomatte for this instead.

[fraggle]

I don't think object ID can work with this, it's an integer channel that can only store whatever object is closest to camera in each pixel. You'll have to use multimatte or cryptomatte for this instead.

Sad, because I do have a lot of different object and I was hoping to get an easy hand on it in Postprod. Multimatte will need a very long setup for a lot of object and as for cryptomatte it won't help much with photoshop Post prod I believe.