Alphas and flipbooks

[revelationsr]

I have a scene i want to do a slap comp. I have an object and a pyro. I would like to know how to make sure the object does not show up in the alpha of the flipbook. Also it seems the pyro has a slight ghost of the object drawn in it despite that  object being shaded black and is behind it.

 

Any thoughts?

 

Cheers.

[jamesr]

Make a pure green (0,1,0) background and use it as the image plane for the camera (camera --> view > background image) and flipbook over that. Then key it out in nuke. 

(You could also color a grid green and parent it to the camera)

 

[jamesr]

Here's a quick example of what I mean

 

Edit: I just realized I forgot to include the part where you ask about holding something out, too

boom_comp.mov

 

 

 

Edited April 4, 2018 by jamesr

[jamesr]

Sorry, here it is with a holdout. Same concept, green box. 

 

boom_comp_holdout.mov

[mcgillk]

I was running into a similar issue a while ago and found a way to pu my sim over my image plate without any sort of compositing. Can't share the file at the moment but here are the steps I used.

1. UV Texture node on the objects you want to make "invisible". For "texture type" put "Perspective From Camera" and drop your camera into the camera field.
2. Create a material with a roughness of 1, no reflectivity, and use your image plate as the base color texture.

Now you've got a camera projection on top of any foreground objects that need to be treated as matte objects for your sim.