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