Matte (filmmaking)
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 with a background image. 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, the director 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. There would be 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, the images can be combined 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 traveling mattes. Traveling mattes enable greater freedom of composition and movement, but they are also more difficult to accomplish.
Compositing techniques known as chroma keying that remove all areas of a certain color from a recording—colloquially known as "bluescreen" or "greenscreen" after the most popular colors used—are probably the best-known and most widely used modern techniques for creating traveling mattes, although rotoscoping and multiple motion control passes have also been used in the past. Computer-generated imagery, either static or animated, is also often rendered with a transparent background and digitally overlaid on top of modern film recordings using the same principle as a matte—a digital image mask.
History
Mattes are a very old technique, going back to the Lumière brothers. Originally, the matte shot was created by filmmakers obscuring the background section on the film with cut-out cards. When the live action portion of a scene was filmed, the background section of the film wasn't exposed. Then a different cut-out would be placed over the live action section. The film would be rewound, and the filmmakers would film their new background. This technique was known as the in-camera matte and was considered more a novelty than a serious special effect during the late 1880s. A good early American example is seen in The Great Train Robbery 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'. Around this time, another technique known as the glass shot was also being used. The glass shot was made by painting details on a piece of glass which was then combined with live action footage to create the appearance of elaborate sets. The first glass shots are credited to Edgar Rogers.The first major development of the matte shot was the early 1900s by Norman Dawn ASC. Dawn had seamlessly woven glass shots into many of his films: such as the crumbling California Missions in the movie Missions of California, and used the glass shot to revolutionize the in-camera matte. Now, instead of taking their live action footage to a real location, filmmakers would shoot the live action as before with the cut-out cards in place, then rewind the film and transfer it to a camera designed to minimize vibrations. Then the filmmakers would shoot a glass shot instead of a live action background. The resulting composite was of fairly high quality, since the matte line—the place of transition from the live action to the painted background—was much less jumpy. In addition, the new in-camera matte was much more cost-effective, as the glass didn't have to be ready the day the live action was shot. One downside to this method was that since the film was exposed twice, there was always the risk of accidentally overexposing the film and ruining the footage filmed earlier.
The in-camera matte shot remained in use until the film stock began to go up in quality in the 1920s. During this time a new technique known as the bi-pack camera method was developed. This was similar to the in-camera matte shot, but relied on one master positive as a backup. This way if anything was lost, the master would still be intact. Around 1925 another method of making a matte was developed. One of the drawbacks of the old mattes was that the matte line was stationary. There could be no direct contact between the live action and the matte background. The traveling matte changed that. The traveling matte was like an in-camera or bi-pack matte, except that the matte line changed every frame. Filmmakers could use a technique similar to the bi-pack method to make the live action portion a matte itself, allowing them to move the actors around the background and scene—integrating them completely. The Thief of Bagdad represented a major leap forward for the traveling matte and the first major introduction of the bluescreen technique invented by Larry Butler when it won the Academy Award for Best Visual Effects that year, though the process was still very time-intensive, and each frame had to be hand-processed.
Computers began to aid the process late in the 20th century. In the 1960s, Petro Vlahos refined the use of motion control cameras in bluescreen and received an Academy Award for the process. The 1980s saw the invention of the first digital mattes and bluescreening processes, as well as the invention of the first computerized non-linear editing systems for video. Alpha compositing, in which digital images could be made partially transparent in the same way an animation cel is in its natural state, had been invented in the late 1970s and was integrated with the bluescreen process in the 1980s. Digital planning began for The Empire Strikes Back in 1980, for which Richard Edlund received the Academy Award for his work to create an aerial-image optical printer for combining mattes, though this process was still analog. The first fully digital matte shot was created by painter Chris Evans in 1985 for Young Sherlock Holmes for a scene featuring a computer-graphics animation of a knight leaping from a stained-glass window. Evans first painted the window in acrylics, then scanned the painting into LucasFilm's Pixar system for further digital manipulation. The computer animation blended perfectly with the digital matte, something a traditional matte painting could not have accomplished.
, nearly all modern mattes are now done via digital video editing, and the compositing technique known as chroma key - an electronic generalization of the bluescreen - is now possible even on home computers.
Technique
In-camera matte shot
The in-camera matte shot, also known as the Dawn Process is created by first mounting a piece of glass in front of the camera. Black paint is applied to the glass where the background will be replaced. The actors are then filmed with minimal sets. The director shoots several minutes of extra footage to be used as test strips. The matte painter then develops a test strip and projects a frame of the 'Matted' shot onto the easel mounted glass. This test footage clip is used as the reference to paint the background or scenery to be matted in on a new piece of glass. The live action part of the glass is painted black, more of the test footage is then exposed to adjust and confirm color matching and edge line up. Then the critical parts of the matted live action scene are threaded up for burning the painted elements into the black areas. The flat black paint put on the glass blocks light from the part of the film it covers, preventing double exposure over the latent live action scenes from occurring.Bi-pack process
To begin a bipack matte filming, the live action portion is shot. The film is loaded and projected onto a piece of glass that has been painted first black, then white. The matte artist decides where the matte line will be and traces it on the glass, then paints in the background or scenery to be added. Once the painting is finished the matte artist scrapes away the paint on the live action portions of the glass. The original footage and a clean reel are loaded into the bi-pack with the original threaded so it passes the shutter in front of the clean film. The glass is lit from behind, so that when the reels are both run, only the live action is transferred to the clean film. The reel of original footage is then removed and a piece of black cloth is placed behind the glass. The glass is lit from the front and the new reel is rewound and run again. The black cloth prevents the already exposed footage from being exposed a second time; the background scenery has been added to the live action.Rotoscoping
The rotoscope was a device used to project film onto a canvas to act as a reference for artists.Walt Disney used the technique extensively in Snow White and the Seven Dwarfs in order to make the human characters' motions more realistic. The film went significantly over budget due to the complexity of the animation.
The technique had a few other uses, such as in 2001: A Space Odyssey where artists manually traced and painted alpha mattes for each frame. Rotoscoping was also used to achieve the fluid animations in Prince of Persia, which were impressive for the time. Unfortunately, the technique is very time-consuming, and trying to capture semi-transparency with the technique was difficult. A digital variant of rotoscoping exists today, with software helping users avoid some of the tedium; for instance, interpolating mattes between a few frames.