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Video Production Glossary
Matte
Mattes are used in photography and special
effects filmmaking 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 this case, the matte is the background
painting. In film and stage, mattes can be physically huge sections of
painted canvas, portraying large scenic expanses of landscapes.
In film, the principle of a matte requires masking certain areas of the film
emulsion to selectively control which areas are exposed. However, many
complex special-effects scenes have included dozens of discrete image
elements, requiring very complex use of mattes, and layering mattes on top
of one another.
For an example of a simple matte, we may wish to depict a group of actors in
front of a store, with a massive city and sky visible above the store's
roof. We would have two images—the actors on the set, and the image of the
city—to combine onto a third. This would require two masks/mattes. One would
mask everything above the store's roof, and the other would mask everything
below it. By using these masks/mattes when copying these images onto the
third, we can combine the images without creating ghostly double-exposures.
In film, this is an example of a static matte, where the shape of the mask
does not change from frame to frame.
Other shots may require mattes that change, to mask the shapes of moving
objects, such as human beings or spaceships. These are known as travelling
mattes. Travelling mattes enable greater freedom of composition and
movement, but they are also more difficult to accomplish. Bluescreen
techniques, originally invented by Petro Vlahos, are probably the best-known
techniques for creating travelling mattes, although rotoscoping and multiple
motion control passes have also been used in the past.
Mattes are a very old technique, going back to the Lumière brothers. A good
early American example is seen in The Great Train Robbery (1903) where it is
used to place a train outside a window in a ticket office, and later a
moving background outside a baggage car on a train 'set'.
Garbage matte
A "garbage matte" is often hand-drawn, sometimes very quickly made, and can
be used to exclude parts of an image that another process, such as
bluescreen, would not remove. The name stems from the fact that the matte
removes "garbage" from the procedurally produced image. This "garbage" might
include a rig that is holding a model or the lighting grid above the top
edge of the bluescreen. Garbage mattes can also be used to include parts of
the image that might otherwise have been removed by the bluescreen, such as
too much blue reflecting on a shiny model ("blue spill").
Mattes and widescreen shooting
Another use of mattes in filmmaking is to create a widescreen effect. In
this process, the top and bottom of a standard frame are matted out, or
masked, with black bars, i.e. the film print has a thick frame line. Then
the frame within the full frame is enlarged to fill a screen when projected
in a theatre.
Thus, in "masked widescreen" an image with an aspect ratio of 1.85:1 is
created by using a standard, 1.37:1 frame and matting out the top and
bottom. If the image is matted during the video production process it is
called a "hard matte." In contrast, if the full frame is filled during
filming and the projectionist is relied upon to matte out the top and bottom
in the theatre, it is referred to as a "soft matte."
In video production, a similar effect is often used to present widescreen
films on a conventional, 1.33:1 television screen. In this case, the process
is called letterboxing. However, in letterboxing, the top and bottom of the
actual image are not matted out. The picture is "pushed" farther back on
screen and thus made "smaller", so to speak, so that, in a widescreen film,
the viewer can see, on the left and right of the picture, what would
normally be omitted if the film were shown fullscreen on television,
achieving a sort of "widescreen" effect on a square TV screen. In
letterboxing, the top of the image is slightly lower than usual, the bottom
is higher, and the unused portion of the screen is covered by black bars.
For video transfers, transferring a "soft matte" film to a home video format
with the full frame exposed, thus removing the mattes at the top and bottom,
is referred to as an "open matte transfer." In contrast, transferring a
"soft matte" film to a home video format with the theatrical mattes intact
is referred to as a "closed matte transfer."
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