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Resolution & Interlacing
Two elements that determine the quality of a TV picture are:
Resolution
If you’ve ever looked very closely at your TV, you have noticed the picture is actually made up of many
lines scanning across the screen. e set of lines that make up a complete image are called a “frame.” For
TV equipment and broadcasts, resolution is defi ned by the number of horizontal lines displayed to make
up each frame of a video image. e more lines of resolution used to compose each frame, the more
detailed and sharp the picture. Standard TV resolution uses 480 horizontal lines to make up each video
frame; HDTV uses either 720 or 1080 lines to compose each frame.
Interlaced & Progressive
e term “interlacing” refers to whether each of those frames contains all of the lines of image, or every
other line. Interlaced signals take every other line from 2 frames, each lasting 1/60th of a second, and
combine them into one frame lasting 1/30th of a second. In this way, interlacing tricks the eye into
thinking it’s seeing twice the resolution that’s actually being displayed. In non-interlaced video, referred
to as “progressive scan” video, frames are displayed every 1/60th of a second containing all of the lines of
video information.
e specifi cations for video resolution are usually stated by giving the number of horizontal lines (480,
720 or 1080, as described above) followed by either the letter “i” (for interlaced) or “p” (for progressive
scan). Most standard TV broadcasts are 480i; some DVDs and non- HDTV digital broadcasts use 480p.
Specifi cation for HDTV broadcasts and equipment requires either 1080i or 720p.