Open matte is a filming technique that involves matting out the top and bottom of the film frame in the movie projector (known as a soft matte) for the widescreen theatrical release and then scanning the film without a matte (at Academy ratio) for a full-screen home video release.
Open matte can be used with non-anamorphic films presented in 2.20:1 or 2.39:1, but it isn't used as often, mainly because it adds too much additional headroom, depending upon how well the framing was protected. Instead, those films will employ either pan and scan or reframing using the well-protected areas. Films shot anamorphically use the entire 35mm frame (except for the soundtrack area), so they must use pan and scan as a result.
The rise of new film exhibition technologies in the 1950s like Cinerama, and anamorphic lenses, shooting wide aspect ratios for theatrical films. This coincided with the rise of television and home media with a much different, narrow aspect ratio of 4:3. To avoid letterboxing for broadcast releases, films were therefore reframed and cropped shot by shot to fit appropriately, and full screen with the 4:3 aspect, with a process called Pan and Scan. Hence, only a cropped small portion of the theatrical frame was broadcast.
Many films over the years have used the open matte technique for home video releases and television broadcasts, the most prominent of which include the Back to the Future trilogy, the Jurassic Park trilogy, Schindler's List, Titanic, and Top Gun as well as many films that have been specially formatted for the IMAX expanded aspect ratio of 1.90:1 and 1.43:1. Stanley Kubrick also used this technique for his last three films The Shining (1980), Full Metal Jacket (1987) and Eyes Wide Shut (1999). Sam Raimi’s Spider-Man (2002) and James Cameron's Terminator 2: Judgment Day (1991) are also examples of open matte.
Usually, non-anamorphic 4-perf films are filmed directly on the entire full-frame silent aperture gate (1.33:1). When a married print is created, this frame is slightly re-cropped by the frame line and optical soundtrack down to the Academy ratio (1.37:1). The movie projector then uses an aperture mask to soft matte the Academy frame to the intended aspect ratio (1.85:1 or 1.66:1). When the 4:3 full-screen video master is created, many filmmakers may prefer to use the full Academy frame ("open matte") instead of creating a pan and scan version from within the 1.85 framings. Because the framing is increased vertically in the open matte process, the decision to use it needs to be made prior to shooting, so that the camera operator can frame for 1.85:1 and "protect" for 4:3; otherwise unintended objects such as boom microphones, cables, and light stands may appear in the open matte frame, thus requiring some amount of pan and scan in some or all scenes. Additionally, the un-matted 4:3 version may often throw off an otherwise tightly-framed shot and add an inordinate amount of headroom above actors (particularly with 1.85:1), depending upon how well the framing was protected. With high definition television now in common usage (with its standardized 16:9 (1.78:1) aspect ratio), the need to reformat 1.85:1 movie for television viewing has virtually evaporated, although television broadcasts still reformat 2.39:1 movie by means of using an open matte or pan and scan. For films with wider aspect ratios (2.39:1, for example) the matting bars will appear on the top and bottom of the screen of the broadcast image, thus preserving each director's framing intent.