AOV’s, Render’s & Light Groups in Nuke
Following the rendering of images from Maya as .exr files, it is now possible to bring the CG assets back into nuke to begin post-production processing of the 3D assets.
Creating a 3D ST Map
Before bringing 3D assets into Nuke, there is a need to set up an appropriate that contains the motion data that will align with both the footage and the CG Assets. Following the same steps highlighted in the 2D Tracking post. Making sure that the output is set to ST Map so that motion data is written into the ST Map.
AOV’s and Renders in Nuke
With each 3D asset, bringing them into Nuke, it is important to ensure that they are properly organised into pairings or groups, depending on whether you have rendered out shadows and reflections to ensure that your node tree is clear for all post-production, at this point it is also useful to ensure that each of the rendered assets is named based on its collection name from Maya ([asset name] Shadow etc) .
To ensure that each of the separate layers (Model, Shadow and reflections) all appear as a group, ensure that a merge node is used to bring each layer together – initially these merge nodes should all be focused on a single set of assets before the final merge is placed for all CG Assets ahead of the CG assets being brought into the 3D ST Map.
Once this has been done, it is important to ensure that all the rendered layers for the surfaces that have data (Diffuse, Specular, Sub-surfaces etc) are identified to ensure that these can be separated out using the shuffle nodes. Setting up these nodes to one for each of the selected surfaces that have data.
At this point, it is also imperative to create a copy node that is directly connected to the CG Read node and is piped in before the premult node to ensure that the Alpha channel from the original read node is copied into the main pipeline.
After this preliminary setup, colour correction and altering of the different channels can be done using the same steps explained in the colour correction and grading post. At this point other nodes such as Glow and Edge Blur can be applied to each of the layers to achieve the desired outcome for the composition, based on initial artistic ideas.
Further Reading and Research
To gain a deeper understanding of the ways in which Nuke can be used for multipass compositing I watched the following youtube videos that provided alternative ways to approach this https://www.youtube.com/watch?v=_kQ-x6CYKXY & https://www.youtube.com/watch?v=sPn0FW5AfVI
In preparation for my final project, which will hopefully include two moving animated assets, I also researched the potential use of the relight nodes and Arnold light groups and how these can be adjusted in Nuke using the two following YouTube tutorial https://www.youtube.com/watch?v=sUzcHzKKalw & https://www.youtube.com/watch?v=YGIdh5W37pQ