Specifications

6
A Digital Video Primer
Another factor to be aware of regarding resolution on digital TVs is the physical size of the
screen. ere are more dots placed horizontally across a 50-inch plasma screen than on a 27-inch
direct-view screen. Although a 1080i image may be fed to an HDTV display, that display may
not be able to reproduce all the dots in the image received. Digital TVs reprocess (upconvert or
downconvert) the image to conform to the number of dots actually available on the screen. A
1080i image created for HDTV with a resolution of 1920 x 1080 may be downconverted to t
1366 x 768, 1280 x 960, 1024 x 768, or any other pixel eld. As you may expect, downconversion
results in a loss of detail.
You may nd yourself working with a wide variety of frame rates and resolutions. For example, if
you are producing a video that is going to be distributed on HDTV, DVD, and the web, then you
need to produce videos in three dierent resolutions and frame rates. Frame rate and resolution
are very important in digital video because they determine to a great extent how much data must
be stored and streamed to view your video. ere are oen trade-os between the desire for great
quality video and the requirements imposed by storage and bandwidth limitations.
More data is required to produce higher-quality images and sound.
Aspect ratios
e width-to-height ratio of an image is called its aspect ratio. e 35mm still photography lm
frames on which motion picture lm was originally based have a 4:3 (width:height) ratio, which
is oen expressed as 1.33:1 or 1.33 aspect ratio (multiplying the height by 1.33 yields the width).
From 1917 to 1952, the 4:3 aspect ratio was used almost exclusively to make movies and to
determine the shape of theater screens. When television was developed, existing camera lenses
all used the 4:3 format, so the same aspect ratio was chosen as the standard for the new broadcast
medium. is 4:3 format is now known as fullscreen TV.
In the 1950s, the motion picture industry began to worry about losing audiences to broadcast
television. So the movie studios began to introduce a variety of enhancements to give audiences a
bigger, better, and more exciting experience than they could have in their own living rooms. One
of those enhancements was a wider screen. Studios produced widescreen lms in a number of
scope formats, such as Cinemascope (the original), Warnerscope, Technicscope, and Panascope.
Widescreen became a hit with audiences, and eventually a standard aspect ratio of 1.85 was
adopted for the majority of lms.
One problem with the widescreen format was that it did not translate well to television. For many
years, when widescreen lms were shown on television, the sides of the image were lopped o to
accommodate the 4:3 ratio of TV. Eventually, letterboxing came into vogue, whereby black bars
were positioned above and below the widescreen image, in order t the full width of the image on
the TV screen.
160
120
240
483
720
1080
352 720 1280 1920
QCIF
176x128
22,528px
CIF
352x288
101,376px
NTSC DV
720x480
345,600px
720
1280x720
921,600px
1080
1920x1080
2,073,600px
16:9 aspect ratio of widescreen TV
4:3 aspect ratio of fullscreen TV
A comparison of the sizes, shapes, and resolutions of
standard frame dimensions: CIF (Common Intermedi-
ate Format), QCIF (Quarter CIF), NTSC DV, and two HD
standard.