An anamorphic image is one where the width of the image has been squeezed to fit into a smaller number of pixels horizontally than the actual display size.
[show a wide image shrinking]. For example, the 2K Cinemascope format has 1828 x 1556 pixels, but is displayed as if there were actually 3,656 x 1556 pixels. Each pixel in he image is effectively twice as wide as it is high in the final displayed image. [see also aspect ratio].
Anamorphic images originated as a way to fit wider images onto a standard 4:3 frame of film. The camera was fitted with an anamorphic lens that squeezed the image, and the movie projector was consequently fitted with another anamorphic lens that stretched the image back to its natural width.
In the digital age, anamorphic formats are still occasionally used to reduce file size. When working with anamorphic formats, most software maintains the squeezed image data for all its processing, only stretching the images on the fly for the operator to preview. This minimizes sub-pixel softening artifacts and maintains image integrity throughout the DI process.