The Matte Learns Only Inside the Band

A bad cutout rarely announces itself as a bad cutout. The car lands on a new backdrop, the paint looks clean, then a thin piece is gone. An antenna. A tire lip. The dark seam under a rocker panel. The complaint that comes back is never technical. The vehicle looks wrong. I wanted the last correction stage to fix fuzzy edges without handing it the whole car to rewrite. That sounds like a small distinction. It stops being small the first time a model improves one boundary and quietly damages another. So the rule is physical. Edit the uncertain strip. Leave the settled area alone. This is Part 2. Part 1, "Negative Space Is a Label", was about supervision: what the pixels beside an object teach a model, and why a shadow touching a tire has to be labeled as evidence against foreground. This one moves from training to runtime. A mask already exists. Where is a learned stage allowed to act? 1. The contract lives in the band CarSegNet is the research implementation here. Its pipeline module splits the route by media type, and the docstring says the design more clearly than any diagram I could draw after the fact. Stills run SAM 3 text concept, then NSJ alpha, then composite. A detector box prompt and a depth prior are optional inputs. Video runs SAM 3.1 multiplex propagation, per-frame NSJ with temporal handling, a depth-parallax plate, composite, encode. The list matters less than the handoff. SAM gives a semantic prior. NSJ receives a trimap band. The compositor receives a matte only after the prior and the refiner have each done bounded work. flowchart TD image[Vehicle Image] segment[Concept Mask] trimap[Trimap Band] refiner[NSJ Alpha Refiner] depth[Depth Prior] composite[Showroom Composite] frozen[Prior Frozen Outside Band] image --> segment segment --> trimap trimap --> refiner image --> depth depth --> refiner refiner --> composite segment -.-> frozen frozen --> composite The diagram is a contract. It is not a model zoo. The refiner edits the uncertain strip. The sema