Course 16: Video-Based Rendering:Acquisition...

Camera issues: Tradeoffs between analog vs. digital caqmeras, resolution vs. bandwidth vs. processing time, color adjustment and calibration, frame vs. field capture (field tear example), 3 CCD vs. 1 CCD cameras (color leak/halo example), zoom lenses and distortion, shutter speed vs. motion blur...

Infrastructure issues: Camera placement (wide vs. narrow base line), bandwidth / time code / sync, diffuse lighting, capture pc's and networking, geo and color calibration.

Example system: CMU virtualized reality lab. First built 1996, now in 3rd gen.

• 1st gen: 3D Dome w/51 b+w cameras, 51 vcr's.
• 2nd gen: 3D Room, 14 hq cameras w/zoom, 25 low res cameras, video stored on 17 PC's, 6 second capacity. Analog images time coded before digitization.
• 3rd gen: 3D Cage, sync+infrastructure from 2nd gen but w/24 PC's, 48 cameras, video written directly to RAID (640x480 30fps), 2-10 hour capacity.

Capture: plan, clean the set, always get clean bg, capture multiple times, playback after capture, "Remember to capture camera calibration information" <-- yeah...;)

Post capture processing: field mode correction, geo calibration, silhouetting.

BGsubtraction from clean plate: diff + levels > contract + expand matte > manual corrections (removing shadows etc.)

Region-based approach to post-processing: Remove shadows by comparing color against bg: shadow color matches clean bg color.