HDTV (and digital TV, DTV, in general_there are some digital TV variants that are not high-definition) is all about giving you a bigger and better picture, better audio, and generally making your TV-watching experience more like a movie-watching experience. In fact, at its best, HDTV is so realistic that it’s often described as “looking through a window”_as if you’re really there, not just watching a program.

HDTV – Video standards
There are three essential concepts to understand when you are comparing different video standards:

HDTV – Resolution:
the number of individual picture elements that make up a TV image. The higher the resolution, the more detailed the image, and the sharper the image will appear.Resolution is defined by one of two factors:

HDTV – Lines
(the number of left-to-right lines the TV can display). CRT-based TVs (tube TVs) are rated this way.

HDTV – Pixels
(the number of pixels across the screen times the number up and down). Fixed-pixel displays (plasmas,LCDs, DLPs and the like) are rated this way.

HDTV – Scan Type
comes in two forms:
Interlaced scan: These TV images are created by lighting up every other row of horizontal lines on the screen in one instant, and then going back through and lighting up the remainder of the lines in the next instant. It happens so fast that your eye can’t really tell it’s happening.

HDTV – Progressive scan:
These systems light all the horizontal lines in the same instant, which can make the image seem “smoother” and more like film (or real life).

HDTV – Aspect Ratio (the shape of your TV picture):
Traditional TVs have a 4:3 aspect ratio (screen shape).

This means that for every 4 units of measure across the screen, you have 3 units of screen height. For example, if the screen is 12 inches wide, it will be 9 inches high. HDTVs have a 16:9 aspect ratio_which makes the screen relatively much wider for the same height, compared to a 4:3 TV. Most movies are widescreen (16:9, or even wider), so HDTVs can display most movies without the annoying “letterbox” black bars on the top and bottom of the screen.

HDTV standards
There isn’t a single “HDTV” standard out there. Instead, ATSC contains many different TV standards (with different resolutions,aspect ratios, and scan types), in fact. Some of these standards are truly HDTV; most are not. In the real world, you will deal with four standards when you try to watch TV content on your HDTV.

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