Case Study: Bloody Day

Project Target & Shot Conditions

The main goal of the project was the creation of a CG helmet (modeled from physical references) to be integrated onto a moving driver's head inside a vehicle. The footage was shot on a Nikon D3200 with an 18-55mm lens.

This sensor and lens combination presented several classic matchmove challenges. Rolling shutter distortion had to be corrected to prevent coordinate jitter. Due to high film grain and sensor noise, white circular trackers were manually placed on the background wall to provide stable anchors for the tracker.

Adopted Workflow

1. Marker Placement: Small tracking markers closer to the lens and larger markers on the distant wall (close markers failed during solve).
2. Object Tracking: Markers placed on the driver's head hood to isolate rotation and translation.
3. Scaling & Scene Prep: Distance measurements taken between background and hood trackers for correct metric scaling.
4. Focal Length Calibration: Shot at a fixed focal length, though snapping a lens checkerboard photo was forgotten on set, forcing a two-stage focal solve.
5. Shutter Prep: Footage shot at 59.94fps to minimize rolling shutter line scan delays.
6. HDR & Mesh References: Captured 360-degree reference photos for lighting reflection extraction (HDR) and helmet modeling reconstruction.
7. Camera & Object Solver: Solved lens distortion profiles, executed camera path solve, solved driver head motion relative to camera, and exported coordinates.

Solver Challenges & Solutions

Low Parallax Shift: Background features were far and flat, making 3D depth calculation difficult. Adding circular markers was critical to stabilizing the solve.

Window Occlusion Roto: Passing vehicles crossed behind the driver, partially revealing tracking markers on the background wall through the car windows. To solve this, precise rotoscoping was performed to mask out moving geometries and prevent tracking corruption.

Clean Plate Rig Removal: Red markers around the driver's neck and a steel spring support had to be cloned and painted out frame-by-frame in post-production to create a clean, natural composite.