Chromakey Technology and Technique HISTORY Schüfftan process Miniatures and mirrors Double exposure Matted cameras Glass Plates Rear projection HISTORY Double exposure Glass Plates Matted cameras Rear projection From Filming the fantastic: a history of visual effects cinematography by Mark Sawicki HISTORY Double exposure Glass Plates Matted cameras Rear projection From Filming the fantastic: a history of visual effects cinematography by Mark Sawicki COLOUR - Selectively defining of a specific colour value - Making specific colour values generate an alpha channel - Using the Alpha Channel to define transparency COLOUR RGB colour space + Alpha Channel Black and white mask dictating transparency RGB RGBA ELEMENTS of the COMPOSIT Source Alpha Plate Final CAMERA and COLOUR SPACE The greater the amount of colour information the cleaner the key - Option A) Use a high-end 4:2:2 camera (Varicam, Sony F900, Panasonic HPX500, Sony PDW700, etc) Option B) Record SDI feed direct form camera to SDI hardware (deck, PC card, etc) Option C) Use a 4:2:0 camera with a high native resolution and large sensor (Sony Ex1, Ex3) High native resolution can make up limitations of colour sampling. 1920x1080 photosites at 420 provides more ‘colour data’ than a less photosites at 422. LIGHTING Screen light Screen light Back Back Fill Key LIGHTING STEPS 1. Light the screen 2. Adjust camera exposure until Zebras show (90IRE) 3. Adjust lighting to make Zebra pattern even across the screen 4. Stop exposure down to loose the Zebra 5. Light the subject with Key, Fill and Backlight 6. White balance for the subject not the screen 7. Adjust Key, Fill and Backlight to match the Plate 8. Check for exposure and clipping 9. Check for Spill DE-SPILL Isolate the screen colour - props - costumes - set pieces Use complimentary colours to de-spill - magenta gels SHOOTING and STAGING Key things to remember... Hair and costume: Choose colours carefully. Tie hair back when you can. Blondes make things more difficult. Avoid ‘shiny things’ Camera movement: Avoid moving camera shots. Motion tracking and match moving makes things much more complex and often requires specialist 3D tracking software. Shutter speed and motion blur: Turn off any kind of in-camera ‘image sharpening’ feature. Use higher shutter speeds (1/75-1/100) or 50p frame rate shooting to avoid motion blur. DoF: Keep your subjects sharp but your screen blurred. Rack-focusing between two subjects in front of a screen is problematic. Don’t use a 35mm adapter; you need as much light and sharpness as possible. READINGS and RESOURCES Greenscreen Checklist http://generalspecialist.com/2006/10/greenscreen-and-bluescreen-checklist.asp Lighting greenscreen on location http://www.lowel.com/edu/lesson_green_screen.html Visual Effects History http://joebruton.com/LensBased_Feb/flash/VisEffects1006.swf Filming the fantastic: a history of visual effects cinematography http://www.scribd.com/doc/12242274/FilmingtheFantasticvisualeffectscinematography Timeline if special effects milestones http://www.pbs.org/wgbh/nova/specialfx2/timeline.html.