anamorphic widescreen

[valencia]

With respect to DVD formats, what is anamorphic widescreen and how does it differ from letterbox?

[Hippy]

Anamorphic from two Greek words, means literally "capable of up-shape". To grasp the need for this you have to know that films for theatre showing use a "wide-screen" format that is not completely compatible with traditional television displays, although the newer wide screen televisions go some way to get round this.

A traditional TV has an aspect ratio (width compared with height) of 4 by 3 (1.333:1) whereas a wide screen TV has an aspect ratio of 16 by 9 (1.78:1) and there are a few steps in between that we needn't get into here.

The film can be put onto the DVD as a 16 by 9 image with black bits at the top and bottom included on the image to make it fit the 4 by 3 TV screen. This is so called letterbox. It would look exactly the same on any display. If the film were encoded with the full 16 by 9 information and the playback displayed everything on a 4 by 3 aspect ratio the picture would fill the screen, but it would be impossibly squeezed in the left-right plane. Now if it were possible for the playback machine to reduce the left-right resolution and reduce the up-down picture size then it would look fine again. In fact it would look like the letterbox version, but with potentially higher definition as the whole bandwidth is devoted to picture, the borders being generated by the playback machine.

Anamorphic encoding does just that. The full digital image is preserved along with information about the aspect ratio of the original, and the playback device adapts to the best display.

This idea was copied from the cinema wide screen (Cinemascope, Panavision etc.) film optical technology developed in the early 1950s in America. The prints for showing in the cinema are on 35mm or 70mm film with a 6 by 5 (1.2:1) aspect ratio but the picture is optically squashed from left to right, and the special lens on the projector stretches the image back out again to 47 by 20 (2.35:1) so it looks fine on the screen.

[valencia]

Wow! Thanks for all your help!