Digital Home Thoughts: Progressive versus Interlaced: 720p versus 1080i

"This depicts how progressive (P) scanning works - see top row - versus how interlaced (I) scanning works - bottom row. People (such as Congressmen) read "our" 720P proposal and "their" 1080I proposal and assume that 1080I is superior because the number is larger. The diagram above shows that this is a fallacy. In the progressive system, 720 lines are presented to the human eye every 1/60th of a second while the so-called 1080I system presents only 540 lines. Therefore a more accurate name for the interlaced system is 540I. It also more accurately represents the fact that the interlaced system is lower in quality than our 720P system. Not only is 720P superior to 540I in quality (note the well-known artifact: interlace flickers), but it is cheaper! And it is naturally compatible with computers (which all use progressive scanning). Now you can understand the title of this page: It is 720P that is greater than 540I - formerly known in old-speak as 1080I."

A very informative site that is a must-read if you're confused about HDTV resolution and what progressive and interlaced mean.