What is the difference between SDTV, EDTV, and HDTV? What is the difference between 480i, 480p, 720p, 1080i, and 1080p?

If you have not been following the changes in television technology in the last few years, the onslaught of new acronyms and terms can be daunting.

The "TV" portion of SDTV, EDTV, and HDTV is what you would expect -- television. SD stands for "Standard Definition", ED stands for "Enhanced Definition", and HD stands for "High Definition".

Before tackling the differences between 480i, 480p, 720p, 1080i, and 1080p -- which in basic terms refer to the width of the image -- it is worthwhile to know that the "i" suffix stands for "interlaced" and the "p" suffix stands for "progressive".

Interlaced means that a single frame of television is presented in two parts -- first the television "loads" every other line of the picture (2, 4, 6, and so on), and then it loads the remaining lines (1, 3, 5, etc). Progressive means that all lines of the picture are loaded simultaneously, which can make a substantial difference in picture quality, particularly with fast moving images -- sports, action movies, and so forth.

SDTV -- which basically is the same as analog television, but transmitted digitally so that there is no signal loss regardless of distance -- is offered in 480i, EDTV is offered in 480p, and HDTV is offered in 720p, 1080i, and 1080p.

However, as of the date last updated (see top), 1080p is not used for broadcasts due to bandwidth constraints, but it is supported by the Blu-ray and HD-DVD standards. There are differences in aspect ratios (4:3 or 16:9) -- the ratio between the width and height of the display -- as well.

The differences between standards are summarized below in this handy chart:

	SDTV	EDTV	EDTV	HDTV	HDTV	HDTV
Width/Scan	480i	480p	480p	720p	1080i	1080p
Resolution	640x480	640x480	720x480	1280x720	1920x1080	1920x1080
Ratio	4:3	4:3	16:9	16:9	16:9	16:9

For more details -- in addition to history and advantages and disadvantages of each standard -- please refer to the excellent Projector Central website.

The Apple TV supports 720p as its maximum standard, and movies purchased from iTunes are encoded at 480p. Consequently, Apple TV might be of most interest to those with an EDTV (480p) or 720p HDTV.