Chapter 1

96 Everything You Ever Wanted to Know About DVD
4:3 aspect ratio) to get 540 lines. On a 1.78 (16:9) display, you get 405 lines.
In practice, most DVD players provide about 500 lines instead of 540
because of filtering and low-quality digital-to-analog converters. VHS has
about 230 (172 widescreen) lines, broadcast TV has about 330 (248
widescreen), and laserdiscs have about 425 (318 widescreen).
Don’t confuse lines of horizontal resolution (resolution along the X axis)
with scan lines (resolution along the Y axis). DVD produces exactly 480
scan lines of an active picture for NTSC and 576 for PAL. The NTSC standard
has 525 total scan lines, but only 480 to 483 or so are visible. (The
extra lines contain sync pulses and other information, such as the Closed
Captions that are encoded into line 21.) PAL has 625 total scan lines, but
only about 576 to 580 are visible. Because all video formats (VHS, laserdisc,
and broadcast) have the same number of scan lines, it’s the horizontal resolution
that makes the big difference in picture quality.
For more information, see Allan Jayne’s TV and Video Resolution Explained
(http://members.aol.com/ajaynejr/vidres.htm).
What’s Widescreen? How Do the Aspect Ratios Work?
Video can be stored on a DVD in 4:3 format (the standard TV shape) or 16:9
(widescreen). The width-to-height ratio of standard television is 4 to 3; in
other words, 1.33 times wider than high. New widescreen televisions,
specifically those designed for HDTV, have a ratio of 16 to 9, that is, 1.78
times wider than high.
DVD is specially designed to support widescreen displays. Widescreen
16:9 video, such as from a 16:9 video camera, can be stored on the disc in
anamorphic form, meaning the picture is squeezed horizontally to fit the
standard 4:3 rectangle. It is then unsqueezed during playback.
Things get more complicated when film is transferred to video, because
most movies today have an aspect ratio of 1.66, 1.85 (flat), or 2.40 (scope).
Because these don’t match 1.33 or 1.78 TV shapes, two processes are
employed to make various movie pegs fit TV holes.
Letterbox (often abbreviated to LBX) means the video is presented in its
theatrical aspect ratio, which is wider than standard or widescreen TV.
Black bars, called mattes, are used to cover the gaps at the top and bottom.
A 1.85 movie that has been letterboxed for a 1.33 display has thinner
mattes than a 2.4 movie letterboxed to 1.33 (28 percent of the display
height versus 44 percent), although the former are about the same thickness
as those of a 2.4 movie letterboxed to 1.78 (26 percent of display
height). The mattes used to letterbox a 1.85 movie for 1.78 display are so
thin (2 percent) that they’re hidden by the overscan of most widescreen