Hello everyone,

its my first time trying to implement houdini vfx in real footage.

I have a small building where the explosion happens, so i modeled it inside Houdini (before i did camera tracking etc), did all the pyro and debris from inside. Right now i want to have render passes containing only Pyro and Rbd, without modeled building object and then composite it to real footage in Nuke. How do i render those separate passes? Many thanks for replies.

look into cryptomattes, it gives you nice masks for objects and/or materials.

easiest is to use Objects tab on Mantra or Karma ROP

remove * from Candidate objects
set Forced Objects to your pyro and debris
set Forced Matte to your building

therefore Pyro and Debris will be renered together, and building will be used as a matte

you can of course separate it more and just render pyro and use debris and building ad a Forced Matte
and with another rop render debris, and use building as a Forced Matte and pyro as Forced Phantom

etc...