Introduction
Resolution & Interlacing
Two elements that determine the quality of a TV picture are:
Resolution
For TV equipment and broadcasts, resolution is defined by the number of horizontal lines displayed to make up each frame of a video image. The 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
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. The set of lines that make up a complete image are called a “frame.” Like a child’s flipbook where the image seems to move as the pages change, your TV displays video by changing these frames at a rate 60 frames per second.
The 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
The specifications 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
6Defining
