Green Screen Prof Oakes

Lecture Outline Intro Definition Terms History Process Lighting and Shooting Practice pulling Green Screen in FCP

Green Screen? Also known as chroma key, blue screen or keying Technique for mixing two or more images together in which one color (or color range) from one image is removed to reveal the image behind it. Today this is an essential part of a method known as Compositing Effects-heavy movies use this method extensively during production. Through the use of green screen, mattes, alpha channels, and CGI animation, there are unlimited possibilities for filmmakers.

Green Screen Process A pre-determined color is completely removed from the image. Usually this is green or blue but is sometimes orange or magenta. Why green and blue? – These are opposite the red and orange found in many skin types – The green (RGB) channel in most cameras is most sensitive The green areas are “pulled” or “keyed” out of the picture, revealing the image behind it. This footage is usually combined or composited with other layers of imagery (still or moving).

Terms to Know Compositing CGI- Computer Generated Imagery Matte (Travelling Matte/)Garbage Matte Alpha Channel RGB Color Rotoscope Flat Lighting/Diffuse Lighting

Brief History Earliest special effects – In-camera effects (Multiple Exposure) – stop camera effects (stop motion) Blue screen (film) Matte effects/Traveling matte Miniatures – Sets- Metropolis – Animation King Kong-Willis O’Brien Jason and Argonauts - Harryhausen Optical Printer Motion Control Cameras CGI – Computer Graphics Imaging

Melies’ A Trip to the Moon

Early Effects Georges Melies (France) was an early pioneer of visual effects. – 500 short films – Multiple Exposures, time-lapse, dissolves, hand- painted film – Le Voyage dans la Lune (1902) A combination of live action and animation. Miniatures and matte painting

Mattes Mattes are a very old technique, going back to the Lumiere Brothers Great Train Robbery (1903) shows a train outside a window in a ticket office During the 1920s and 1930s, special effects techniques were improved and refined by the motion picture industry. Rear Projection substituted painted backgrounds with moving backgrounds

Matte The background layers are often referred to as mattes in both still photography and motion pictures Mattes are used to combine two or more image elements into a single, final image. Usually, mattes are used to combine a foreground image (such as actors on a set, or a spaceship) with a background image (a scenic vista, a field of stars and planets). In film, the principle of a matte requires masking certain areas of the film emulsion to selectively control which areas are exposed.

Traveling Mattes Color photography enabled the development of traveling matte techniques such as blue- screen The Thief of Bagdad (1940) used this technique The Ten Commandments (1956) – Multiple Crowds and architecture – Parting of the Red Sea

The Ten Commandments

Miniatures Ray Harryhausen extended the art of stop-motion animation with mattes – The 7th Voyage of Sinbad (1958) – Jason and the Argonauts (1963) 2001: A Space Odyssey (1968) – Established a new high-bench mark for special effects – Spaceship shots created through minatures, hand-drawn rotoscopes, and motion control cameras.

Optical Printer Essentially, an optical printer is a projector aiming into a camera lens, and it was developed to make copies of films for distribution. Linwood G. Dunn (A.S.C) was an early innovator in using the optical printer for special effects – Citizen Kane (1941) “Deep focus” Xanadu scenes

Optical Printer

Motion Control Camera Effects

Motion Control Star Wars (1977) – George Lucas – Industrial Light and Magic founded – John Dykstra – Computer controlled camera rig “Dykstraflex” – Travelling-matte compositing Close Encounters of the Third Kind (1977) – Steven Spielberg – Douglas Trumbull developed his own motion-control system developed techniques for creating intentional lens flare

Digital Filmmaking CGI backgrounds, props, effects, and characters Blending of animation and live action Motion Capture Independent Features - Robert Rodriguez “Sin City” and “300”

Alpha Channel To store matte information, the concept of an alpha channel was introduced by A.R. Smith in the late 1970’s and developed in the 1980’s. In a 2D image element, which stores a color for each pixel, additional data is stored in the alpha channel with a value between 0 and 1. – A value of 0 means that the pixel does not have any coverage information and is transparent. – A value of 1 means that the pixel is opaque.

Alpha Channel

Lighting The screen needs to be EVENLY LIT - (No Shadows/Highlights) Consistency of color is the goal Dull GS materials (Canvas) are preferable 2 or more lights needed Green screen should be BRIGHT (2 F-Stops higher than subject) The Actor should not cast shadows on the screen The actor should avoid wearing green or blue

Common Problems Removing part of actor Green halo/artifacts/Edges (hair) Noise on the subject, especially on edges Green reflection on actor

Exercise Practice with “Stacy” footage Set up the green screen in 439 Shoot footage “Key”out the green screen in FCP Add whatever elements you want to the background.