What Exactly is HDTV?

The most difficult thing to judge when shopping for a TV is how good the picture looks. Good is a subjective term, so relying on the judgment of reviewers may not get you exactly what you want. Then again, many reviewers scoff at the kinds of pictures that impress TV shoppers in the store. In this section, we'll offer some tips on how to become a more discerning viewer and what separates good pictures from the rest.

1. Display resolution

HDTVs come in display resolutions of 720p (720 lines of detail) or 1080i/p (1,080 lines of detail). A standard-definition (SD) TV has 480. The "p" refers to progressive scan, in which each of the picture frames that appears is drawn line by line from top to bottom on the screen, causing onscreen action to appear smoother. The "i" stands for interlaced, meaning that every second line of a picture is drawn in sequence.

Those models with non-standard resolutions scale the incoming video signals to fit the available pixels, throwing away information if they have fewer pixels and interpolating information if they have more pixels than the source.

Native resolution	Commonly called	Meets definition of high-def?	Frequency	Typical TV types
1,920 x 1,080	1080p	Yes	Increasingly standard, especially for 32-inch and larger TVs	Flat-panel LED, LCD and plasma
1,366 x 768	768p	Yes	Getting less common these days, mainly for LCD and smaller TVs	Flat-panel LCD; 50-inch plasma
1,280 x 720	720p	Yes	Common in rear-projection, but not flat panels	DLP, LCD, and LCoS projection
1,024 x 768	XGA	No	Standard plasma resolution	42-inch plasma

HDTVs that display 1080p content are becoming standard in the HD world. They're said to be the best for TV viewing since they combine the smooth images of progressive scan and the sharpness of 1,080 lines of resolution.

2. Aspect ratio

Movies, commercials and TV shows filmed in HD have a wider aspect ratio (the ratio of a screen's height to its width) than their SD counterparts. HD display width divided by its height is denoted as 16:9 compared with SD's 4:3 ratio. The net result is a rectangular, widescreen format for all HDTV panels and content.

More often than not, anamorphic movies are produced in various ultra-wide formats originally intended for screening in cineplexes and theaters. These normally result in top and bottom black bars when played back on HDTVs, a bottleneck which can be partially overcome with inbuilt aspect ratio settings.

3. HD tuner

To see the mutilated corpses of CBS' CSI crime drama series in stomach-turning detail or to count freckles on the faces of the Grey's Anatomy medical series' cast requires an HDTV, HD settop box and external antenna. An HD tuner-integrated TV or Integrated Digital TV (IDTV) requires only an external antenna. You will also need to sign up with an HD broadcast provider in your country to receive these programs.