Anamorphic widescreen can refer to either a technique of motion picture cinematography that captures a widescreen image on standard 35mm film, or a similar principle applied to DVD recordings to allow for the best picture quality possible. In either case, it involves the compressing or "squeezing" of a widescreen image to maximize resolution.
This technique was first used in motion picture cinematography in the 1950s. Standard 35mm motion picture film has an aspect ratio of 1.37:1, meaning it is 1.37 times as wide as it is tall. Widescreen is 2.39:1, however, meaning it is wider than the film negative. Prior to the development of the anamorphic technique, rectangular widescreen images had to be recorded on 35mm film so that their full width fit on the more square-shaped negative, with unused portions above and below the image. The image on the negative resembles a small rectangle within a larger, square frame.
Anamorphic widescreen uses the entire frame by vertically stretching the image to fit on the negative. This is accomplished with special lenses that compress the image as it is filmed. To correct the distortion caused by a 2.39:1 image being stretched to fill a 1.37:1 frame, another lens, this one on the theater's projector, is used to correct the picture's proportions. The resulting image has greater resolution because more film area is being used to project the same picture.
This technique works similarly when applied to DVD. Conventional analog televisions have an aspect ratio of 4x3, or 1.37:1, and therefore have the same problem accommodating widescreen images as 35mm film. A video image not recorded in anamorphic widescreen looks much like a non-anamorphic film negative: the full width of the image is presented with black bars at the top and bottom. On non-anamorphic or "letterboxed" DVDs, these bars are present in the DVD signal.
Anamorphic DVDs record a vertically stretched image that fills an entire 4x3 frame. When played back on a 4x3 television, the DVD player restores the correct aspect ratio and generates black bars at the top and bottom of the frame, and it looks much like a letterboxed DVD. On a widescreen (16x9) television, the difference is obvious, however. The television, much like an anamorphic projection lens, restores the image to its original proportions and, depending on the aspect ratio of the film, displays smaller or no black bars because both the television screen and movie are widescreen. Non-anamorphic video played on the same television has not only the black bars at the top and bottom, but gray bars on the left and right because the video signal is more square than the television screen.
Anamorphic widescreen DVDs are usually labeled "anamorphic" or "enhanced for 16x9 televisions." Because all digital televisions are 16x9, this type of DVDs have less chance of becoming obsolete in the wake of the digital TV conversion.