When buying an HDTV display, look for key features that will give you the best quality images. Moving up to HDTV capabilities isn't much of a price jump, and in fact, you probably can't find a TV that’s bigger than about 20 inches and not an HDTV.
Key characteristics
An HDTV has the following key characteristics:
Resolution: Can display true high-definition signals with at least 720 lines of horizontal resolution (in other words, 720 lines of picture data stacked on top of each other vertically on the screen). The latest and greatest HDTVs can display the full 1920 x 1080 pixels of 1080i and 1080p HDTV signals. Such HDTVs are often called 1080p HDTVs.
Aspect ratio: Has a widescreen aspect ratio of 16:9.
Tuner: Has a built-in TV tuner, which is capable of decoding any over-the-air broadcast format within the ATSC digital television standard.
An HDTV-ready set must meet only the first two requirements — in other words, there’s no TV tuner in an HDTV-ready system. Direct-view, flat-panel, front-projection, and rear-projection display systems can all be built as an HDTV or HDTV-ready system. And just like non-HDTV versions of these displays, a huge range of sizes and shapes is on the market.
Features to look for
Beyond the physical type of TV and the actual picture quality of the TV (which varies, based on the type of TV and specific engineering and design decisions made by the manufacturer), you should consider specific features and specifications when looking at HDTVs.
The following features and characteristics apply across the different types of TVs (LCD, plasma, and so on) unless otherwise specified:
HDTV versus Full HD HDTV: All HDTVs have a display resolution of at least 720p (1280 x 720 pixels). Those TVs which have a resolution of 1920 x 1080 are often described as Full HD HDTVs. If you absolutely have to have the latest and greatest thing — or if you’re going to have a particularly large HDTV for your home theater room — you should definitely get a Full HD 1080p set. Otherwise, you may be perfectly content with a 720p display.
Supported input resolutions: Just as HDTVs have a display resolution (the number of pixels on the screen), they also have supported input resolutions — the resolutions of incoming TV signals that the TV can accept and convert to the display resolution. Many HDTVs (even those with a display resolution of 1080p) can’t accept a 1080p, for example.
For Blu-ray discs, you should consider an HDTV that has Full HD capabilities, supports 1080p input resolutions, and can support 1080p24. 1080p24 (the 24 refers the frame rate) is a special mode in Blu-ray discs that matches the frame rate of the video to the frame rate used to record movies on film.
Deep color support: Most high-definition TV sources have a color depth of 8 bits per color (or 24 bits for red, green, and blue combined). Some high-end HDTVs support a system called deep color (or, in tech terms, xvYCC). Deep color takes the color depth to 10, 12, or more bits — meaning that video is then capable of supporting millions of colors.
120 Hz refresh: Common video sources (including HDTV) have frame rates between 24 and 60 frames per second. A number of LCD TVs are designed to play all signals coming into the TV at 120 frames per second. They do this by using some high-powered chips and some sophisticated math to interpolate what the picture would look like if it was recorded at 120 Hz (120 times per second). This faster refresh rate is designed to overcome a limitation of LCD TVs — namely that they have a slower response time to moving images on the screen than other TVs.
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Source:http://www.dummies.com/how-to/content/what-to-look-for-in-an-hdtv.html
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