When viewing
Anamorphic (16:9) video on a
4:3 TV, the image must be squeezed vertically in order to correct the
Aspect ratio (AR), which is different than the
AR of your TV screen. If you think in terms of square
Pixels. For a
NTSC TV you'd have a horizontal
Resolution of 640
Pixels (480 x 4 / 3). For a 640 pixel wide screen, the center 360 horizontal lines make up the
16:9 area of the display. If your
DVD player were to handle this the same way as it would for a
16:9 screen it would look like the image below. Notice that it appears horizontally squeezed. The face is too tall and skinny. Instead, your
DVD player will squeeze the video vertically and add borders to the top and bottom, preserving the original
AR and compensating for the different screen shape. These borders are known as a Letterbox.
Above is the
Frame displayed with its original height, as stored on an
Anamorphic (Widescreen) DVD. Below is the same
Frame, squeezed vertically to maintain proper
Display Aspect Ratio (DAR). Click on either image to see a larger version.
Letterbox borders are also used to
Encode Widescreen images to a
4:3 video frame for DVD. If the example frames above were from a DVD encoded
Fullscreen, rather than widescreen, the original frame would look like the bottom image with the correct AR for a 4:3 TV used.
Related Guides
Resizing DVD-Video To Square Pixels
Digital Video Fundamentals - Resolution and Aspect Ratio
Related Hardware
16:9 HDTVs
