Back Projection
Back projection is used mostly for shots inside moving vehicles, where slight loss of image quality is less noticable because of the windshield between the camera and the screen.
The system has also been used for stop-motion effects work. Actors in the foreground can act with a back-projected (eg. stop-motion animated)
creature or the footage of the actors can be back-projected, a frame at a time, onto the screen so that they can be combined with stop-motion creatures
animated frame-by-frame in the foreground.
The back-projected footage originally looked less bright than the rest of the scene, but this was improved on in the 1940's with the devolpment of the 'triple-head' process. This used one projector shining light directory onto the back of the screen, and two more on both sides, bouncing identical images from mirrors, so they were superimposed precisely. This created a brighter picture.
Blue (or Green) Screen
A system which replaces a specified colour (blue in this case) with images from another source. This can either be done optically (eg. using film) or electronically
(eg. in video, also known as Chroma-Key in video). Some computer systems look at pixel in the scene and determine whether to replace that pixel with
the other video source. Better computer systems allow 'some' of the colour of the pixel from 1 image and 'some' from another image. The better systems
could be take transparent objects (eg. bottles) or smoke and combine these with the images from another source.
Chroma-Key
Keying out parts of an image which contain a particular colour (or colours). Eg. replacing a blue or green background with images from another source.
C.G.I.
Computer Generated Imagary. The effects created by computer, eg. the 3D rendered graphics, etc.
Composite/Compositing
Combining 2 or more images together into 1. Can be done optically or using a computer.
Digital Matte Painting
A painting created on a computer where parts of the painting will contain the live-action footage. Used in replace of traditional matte
paintings (which were normally done on large sheets of glass).
Go-Motion
Similar to 'Stop-Motion', but the animation is produced by rods attached to the pupet/creature, which can be programmed by a computer
to perform the required movement. The advantage over stop-motion is that a lot more realistic movement can be created, because
the puppet/creature blurs slightly between each frame. The disadvantage is that the rods attached to the creature need to be hidden from
view (e.g. using the blue-screen process).
Freezing Time
An effect where time appears "frozen" (eg. for a few seconds or more). If the camera appears to be moving, this will generally be done by using multiple
cameras (see TimeTrack). If the camera isn't moving, then the same frame is simply being repeated for the length of the shot.
Front Projection
The system used for some of the flying scenes in Superman (1978) and also for the opening scenes in 2001: A Space Oddessey. In this system, the 'background' footage is projected first onto a mirror, then onto a two-way mirror placed between the actor and the camera. This way the image from the projector appears on the screen behind the actor, and the camera records both that image and the actor.
Luma-Key
Keying out parts of an image which are a specified brightness level.
Matte
Usefull in compositing so the area to be keyed out can be drawn by hand.
Matte Painting
A painting done for feature film use which is intended to look like part of the actual film, usually done on a large sheet of glass.Gaps are left in the
painting so that that live action footage can be projected through the glass. If the painting is of (for example) a city, small holes can be created in
the painting, and a light shone from the back so that thousands of lights from the city show through.
Matte paintings are currently being replaced by Digital Matte paintings.
Motion Capture
The process of recording the data from human movement so that it can be used for 3D characters created on a computer.
This can be used for 3D animations for film, TV and games, and also for special effects work.
There are wireless, magnetic motion capture systems, and also optical systems, which track markers attached to the animator.
Motion Control
Controling the motion of a camera or special effects object (eg. model space ship etc), using commands from a computer, so that the exact moves can be repeated as many times. This makes it easy to composite it (ie.combine it with another shot).
Rostrum
A film (or video) camera anchored on a stand which gives movement to the camera. This is used for animation, and also for filming matte paintings, etc. which require camera movement. Professional rostrums are adapted for computer control. All camera and table movements, including the shutter controls can be programmed before the start of the shoot.
Rotoscoping
Drawing around something in the frame so that an effect can be applied to that part of the film.
If an animated creature has to go behind something in the live action piece of film, that object can be drawn around so a matte can be created, so that the createure will not show over the top of that object. If the camera is moving, then each frame of film would have to be rotoscoped. If the camera is still, then the same matte can probably be used for all frames in that shot.
Rotoscoping was first used by the Fleischers for making cartoons. The Fleischers invented the Rotoscope, which is a device for projecting live-action film on to paper frame by frame, so that the outline could be traced and used as a guide for the animation.
The Rotoscope consists of an animation camera and a light source (usually using a prism behind the movement and the lamp house attached to the camera's open door) that projects a print through the camera's lense and the projected image is then traced to create a matte. The lamp house is then removed and the raw
stock placed in the camera and the drawings are filmed through the same lense that projected the image. The resulting image will then fit the original image if the two strips of film are run bi-packed in the same projector movment (using an optical printer).
In digital film effects work, rotoscoping refers to any drawn matte, as both images can be seen compisited while the matte is being drawn, so good results can be achieved.
Stop-Motion Animation
Moving a special effects puppet or model/creature a small amount and recording a single frame (or small number of frames) so that when the film is played back at a normal speed it appears to move. The disadvantage with this form of animation is that it can sometimes appear to 'strobe', partly due to the lack of blur between the frames. See 'Go-Motion'.
Talent
An actor/actress/extra in your film.
TimeTrack
A system by which time appears to "freeze" while the camera keeps moving. It involves using a series of film cameras (more than 10) placed in a line or arc. All cameras film simultaneously, and are therefore all recording exactly the same moment in time. When moving between the shots from the different cameras, taking those frames which were recorded simultaneously, the camera appears to record things "frozen" in time. This is used for films (eg. Batman and Robin) and commercials.
Travelling Matte
A 'moving' matte. Allowing spaceships etc. to move across the screen.
Virtual Sets
Sets which are generated (at least partially) from data within a computer. Mostly used for TV work, these systems replace the real set
(eg. an empty studio) with a computer generated set, allowing the actor/presenter to move in the foreground. eg. the background is 'keyed out'
and replaced with the set which has been created in a 3D package (eg. Softimage or 3D Studio Max), and any camera movements will be duplicated by the 'virtual camera'. This will require a powerful computer, especially if it is to be done in real-time, for example a Silicon Graphics machine.
The method of keeping track of the camera movement (so that it can be duplicated in the 3D computer set) is different for the various sytems. Some
systems use a blue grid painted on the back wall of a studio of a known size. A red LED is projected onto the cameras and the actor/presenter so that they too can be tracked throughout the set.
Vistavision
A film-format which uses the normal 35mm film but uses special cameras to record the images vertically rather than horisontally.
It is used a lot in special effects because of the increased film size, so it will reduce the amount of 'grain' built up through the many compositing stages.
Wire Removal
Removal of unwanted wires, rods, etc. from a piece of film by replacing them with what would have been seen if they weren't there (eg. the background).
This can be done by replacing them with the same area from another frame in which the wires/rods were not visible, or by averaging the colours on either side
of the wire and replacing it with the average.
