First, the basics. Every HDTV has what’s referred to as a native resolution. This is the only resolution the television can display. Every broadcast it receives or digital format it displays (such as a DVD), must all display in the native format. To do this the HDTV converts any signal that differs from its native resolution to the native resolution. Lower resolutions are “upgraded” and higher resolutions are “downgraded.” This process is known as upconverting and downconverting.
In the switch from standard definition broadcasts to high-definition broadcasts, there are competing formats. Some networks broadcast in 720p (1280 x 720) and others in 1080i (1920 x 1080). A 720p HDTV will be able to display 720p broadcasts natively. Displaying a signal without conversion results in an excellent picture. Once the TV has to convert a signal, the conversion process itself can degrade picture quality. Therefore a 720p broadcast might look better on a 720p TV than on a 1080p, if the processor chip in the 1080p HDTV is not up to snuff.
Other networks broadcast in 1080i, which the 1080p HDTV can display natively. A 720p set will have to downconvert a 1080i signal before displaying it. Both HDTVs will also have to de-interlace the 1080i signal but this does not involve changing the resolution, only reordering frame display. An interlaced signal is designed to paint every other line on the display, then fill in the missing lines. Progressive scan TVs paint the screen sequentially, from top to bottom, reducing the flicker affect of interlaced signals.
So far it might sound like a wash. A 720p HDTV will display 720p broadcasts natively, and a 1080p will display 1080i broadcasts natively. The 1080p might be seen as having the advantage that it will also upconvert 720p signals to 1080p resolution, and if the internal processing chip is a good one, this should improve picture quality to lessen "stair stepping" and the "screen door affect" by packing more pixels into the image for an overall smoother quality. Meanwhile, the 720p set will have to downconvert 1080i broadcasts
But the real advantage of the 1080p is in watching HD DVD and Blu-ray discs. These digital discs are formatted in 1080p and studio movies on this media played on the 1080p HDTV are astounding. A 720p set that will accept a Blu-Ray signal must downconvert these formats to lesser resolutions, robbing the viewer of the true Blu-ray / HD DVD experience. The 1080p is also a preferable set for gamers who intend to connect a PC, XBox™ or PlayStation™.
All else being equal, 720p HDTVs are less expensive than their higher resolution siblings. If you aren’t big on DVDs and don’t plan on buying a Blu-ray or HD DVD player, you might opt to save some money. For gamers or movie fanatics, consider the higher resolution set, but stick with a quality brand that will provide a solid upconverter for all of those 720p broadcasts you’ll be watching between movies. Also, be sure the 1080p HDTV provides 1080p inputs or ports. Accepting 1080p input (as from a Blu-Ray player) is a different function than upconverting broadcast signals, and some earlier models lacked the ability to accept 1080p signals.
