Smart vector is a powerful and expensive node in nuke for difficult tracking of face.
Sometimes we may use a combined method to do the tracking with the help of swith node.
Mocha is also a good plugin for tracking.
Smart vectors are usually used in beauty work:
Beauty work in reference frame
We do all the beauty work in a reference frame.
The first step is always denosing the plate. In this case we use denoise node as well as median node, they are both heavy-working nodes and median node is a kind of filter node.
We clean up the plate afterwards. With rotopaint node, we clone for large flaws, remember to set the output in RGBA-alpha channel.
Also we have a excellent gizmo node called VanityFix, it works perfectly with tiny and high-intesity flaws.
We union those alpha outputs and premult them.
Denoised Plate Without VanityFix With VanityFix
Tracking with smart vectors
SmartVector node may take some time to run, depending on machines. The best extension for vectors file is .exr.
Then we will use VectorDistort node to track the face directly, and regrain to match the original plate.
The final step will be merge the beauty work with the original plate, we can merge it twice, the last one is used to recover some imperfection to make the final plate more believable.