USE 3D MODELS AS GRAPHICS IN NUKE
01 IMPORT AN ALEMBIC INTO NUKE
This tutorial uses Nukex, but the experience should be the same for Nuke Indie users. A new Nuke Comp has been created into which has been placed a 32-bit colour 'Beauty pass' of a room with a TV screen, with no other passes. An Alembic file has been exported from the 3D scene with the full range of animation of the camera. This is then dragged onto the Node graph in Nuke from the finder or explorer, or via a Readgeo node.
02 IMPORT ONLY THE SELECTED ELEMENTS
When the Alembic file is imported, a dialog appears which allows an artist to decide which elements are required in the Nuke Comp. In this case, only the Screen shape for the TV and camera are needed, so those are highlighted. Select 'Create parents as separate nodes' to import these two elements into Nuke, as an all-inone node imports every part of the scene as a single node.
03 CREATE A 3D SCENE WITHIN NUKE
Now we have two nodes, a camera node and a Readgeo node which contaminates the mesh for the TV screen. We need an additional node, the Scanlinerender. This node translates the 3D scene into a 2D image. Make sure that the Project settings and camera fps match those of the original scene file. It ensures that there isn't any mismatch when it comes to compositing onto the backplate.
04 OVERLAY THE MODEL ONTO THE BACKPLATE
To apply the Cryptomatte to the Beauty pass, add a Copy node and plug the Beauty into the 'B' pipe and the Scanlinerender into the 'A' pipe of a Merge node. In this example, a square UV image has been applied to the Readgeo node to check the texture placement. As can be seen, Nuke has now applied the image to the scene. The scene is now ready for colour correction and compositing work.