Video resolution is one of those “fuzzy” things in life. It
is common to see video resolutions of 720 x 480 or 1,920
x 1,080. However, those are just the number of horizontal
samples and vertical scan lines and do not necessarily
convey the amount of useful information.
For example, an analog video signal can be sampled
at 13. 5 MHz to generate 720 samples per line. Sampling
the same signal at 27 MHz would generate 1,440 samples
per line. However, only the number of samples per line has
changed, not the resolution of the content.
Therefore, video is usually measured using “lines of
resolution.” In essence, how many distinct black-and-white
vertical lines can be seen across the display? This number
is then normalized to a 1:1 display aspect ratio (dividing
the number by 3/4 for a 4: 3 display or by 9/16 for a 16: 9
display). Of course, this results in a lower value for
widescreen (16: 9) displays, which goes against intuition.
Standard definition video is usually defined as having
480 or 576 interlaced active scan lines and is commonly
called 480i or 576i, respectively.
For a fixed-pixel (non-CRT) consumer display with a
4: 3 aspect ratio, this translates into an active resolution of
720 x 480i or 720 x 576i. For a 16: 9 aspect ratio, this translates into an active resolution of 960 x 480i or 960 x 576i.
Enhanced definition video is usually defined as having
480 or 576 progressive active scan lines and is commonly
called 480p or 576p, respectively.
For a fixed-pixel (non-CRT) consumer display with a 4: 3
aspect ratio, this translates into an active resolution of 720
x 480p or 720 x 576p. For a 16: 9 aspect ratio, this translates
into an active resolution of 960 x 480p or 960 x 576p.
The difference between standard and enhanced
definition is that standard definition is interlaced, while
enhanced definition is progressive.
High definition video is usually defined as having 720
progressive (720p) or 1,080 interlaced (1,080i) active
scan lines. For a fixed-pixel (non-CRT) consumer display
with a 16: 9 aspect ratio, this translates into an active
resolution of 1,280 x 720p or 1,920 x 1,080i, respectively.
However, HDTV displays are technically defined as
being capable of displaying a minimum of 720p or 1,080i
active scan lines. They also must be capable of displaying
16: 9 content using a minimum of 540 progressive (540p)
or 810 interlaced (810i) active scan lines. This enables
the manufacturing of CRT-based HDTVs with 4: 3 aspect
ratios and LCD/plasma 16: 9 aspect ratio displays with
resolutions of 1,024 x 1,024p, 1,280 x 768p, 1,024 x 768p,
and so on, lowering costs.
Audio and Video Compression
The recent advances in consumer electronics — such
as digital television, DVD players and recorders, digital
video recorders, and so on — were made possible due to
audio and video compression based largely on MPEG-2
video with Dolby® Digital, DTS®, or MPEG audio. New
audio codecs (such as MPEG- 4 HE-AAC and WMA Pro)
and new video codecs (such as H.264 and SMPTE VC-1)
offer much better compression than legacy codecs for the
same quality. These advances are enabling new ways of
distributing content (both to consumers and within the
home), new consumer products (such as portable video
players and mobile video/cell phones), and more
cable/satellite channels. NV
About the Author
Keith Jack is the author of Video Demystified and Director of
Product Marketing at Sigma Designs, a leading supplier of Digital
Media Processors that provides high quality processing of H.264,
WMV9/VC-1, MPEG- 4, MPEG-2, MPEG-1, and content. In his
previous career in marketing and chip design, he was involved in
bringing over 30 multimedia chips to the consumer market.
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