2.39:1 is an aspect ratio used in cinematic films, with the image 2.39 times as wide as it is tall. The format comes about from using anamorphic lenses with standard 35mm movie film. An anamorphic lens essentially stretches or compresses light in one dimension. The light coming into the camera is squeezed horizontally, allowing a widescreen image to fit on a normal film negative. Since the standard negative has a 1.37:1 ratio, an anamorphic lens that doubles the horizontal aspect would result in a 2.74:1 ratio. 2.39 was reached as an industry compromise due to the use of non-spherical lenses and space on the negative needed to store sound data. When these films are played back, another anamorphic lens in the projector stretches the image out to its original ratio.

As 2.39:1 is a wider picture format than the 16:9 used in high definition displays, content played back on them will have letterboxing at the top and bottom of the screen.