Curly Hair, Motion Blur and a 96-Frame Hero Shot
You are a roto artist at a mid-sized VFX studio in Mohali. Shot A010 is 96 frames at 4096×2160, 24 fps: a woman with curly hair turns her head against a green screen. Frames 41–58 carry heavy motion blur from a 180-degree shutter. The comp supervisor needs a hair alpha plus a separate garbage matte for a rig visible near the left shoulder. The producer has booked six hours. A junior artist proposes one spline around the entire head with a 12-pixel feather, arguing that 'the comp will fix the rest.' The green screen is uneven, with a dark patch behind the left shoulder. The downstream keyer is already failing on fine flyaways. Internal review is in three hours; final delivery is tomorrow at 10:00. The supervisor says, 'Just get it close; we will clean it in comp.' You have a Wacom tablet, Nuke and Silhouette, and one render node. What do you do?
1. How would you break down this shot, and what spline and keyframing strategy would you use for the curly hair and the motion-blurred frames? Justify your choices in terms of the downstream key.
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Plan in layers, not one shape. I would separate the head and scalp core, the hair mass, three or four flyaway clusters, the left shoulder, and the rig. A single 12-pixel feather would blur flyaways into the green and make the downstream key fail; it would also chatter as the head turns. The core and hair mass get tight splines with 1–2 px feather. Flyaways get small, thin shapes only where they affect the silhouette; I would not roto every strand. On frames 41–58 I would animate the core shape every frame because the head moves too far for reliable interpolation. For motion blur, I would roto the sharp core and match the blur in comp using directional or vector blur, or build a second blurred matte from the core. Rotoing individual blur streaks is slow and usually wrong. The dark green patch needs a separate holdout shape because the key cannot separate it. I would label the hair alpha and garbage matte as separate outputs and test both over bright green, mid-grey and black before review.
2. At the 3 pm review, what do you show and what do you say to the supervisor who wants 'close enough'?
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I would not argue abstractly; I would show a split-screen. On one side, the junior's single feathered spline keyed over bright green, with lost flyaways and a soft halo. On the other, the layered matte with core and flyaway shapes. I would also show the alpha alone and a downstream key test. I would say: 'Close enough fails here because the keyer uses the alpha to suppress green; a 12-pixel feather contaminates the edge and costs the comp team more time than a clean core matte.' Then I would propose a staged deliverable: locked core and garbage matte at 3 pm, hair detail pass by 6 pm, final QC by 8 pm, leaving buffer before 10 am. I would ask the comp artist to test the core matte immediately so we are not guessing. I would record the decision and time estimate in the shot notes, and ask the supervisor to confirm priorities in writing. This keeps the deadline realistic without pretending the first version is final.
3. The plate has a slow camera push-in, and the rig crosses the hair for 12 frames. How do you keep the garbage matte from slipping without over-keyframing?
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I would track the rig with a small 2D point track on a high-contrast area, parent the garbage-matte shape to that track, and keep a manual offset shape for the frames where the rig passes behind hair. I would check every 8–10 frames rather than trusting the track blindly, because a slow push-in changes scale slightly and a point track can drift. For the 12 crossing frames, I would keyframe the shape's edge to follow the hair silhouette and use a separate holdout so I do not destroy the rig matte. I would avoid keyframing every point on every frame; instead I would use fewer points with careful animation, then check the matte over a bright constant and against the plate. Finally, I would label the rig matte as a separate output and note the crossing frames in the shot notes for the comp artist.