Somewhere in every campaign there is one frame that decides what the rest look like. Naming it early and treating it as a reference makes that decision explicit instead of emergent.
In generative production the hero frame does a second job: it becomes the grading reference for the whole set. Grading each clip to look good on its own produces nine slightly different blacks; grading everything to the hero produces a campaign.
It is not the same thing as a master plate. A plate fixes what the product is. A hero frame fixes what the world looks like.
How is a hero frame different from a master plate?
A master plate is a flat, deliberately unglamorous reference for the product’s geometry and labelling. A hero frame is the finished, fully lit image that sets the tone the rest of the set is graded and composed against.
When should the hero frame be locked?
Before the bulk of the set is generated. Locking it afterwards means re-grading everything to match a decision made late.