High Definition Compared to Standard Definition
(Measured in Pixels)
1. Standard Definition (SDTV) - DTV: 480i (720 x 480, interlaced)
2. Enhanced Definition (EDTV) - DVD:
480p (720 x 480, progressive)
480p-wide (854 x 480, progressive)
3. High Definition (HDTV) – DTV, HD Discs:
720p (1280 x 720, progressive)
1080i (1920 x 1080, interlaced)
1080p (1920 x 1080, progressive)
4. High Def DVD - Blu-Ray only
Aspect Ratio
The term Aspect Ratio refers to the width of a picture (or screen) in relation to its height.
Ratios are expressed in the form "width x height".
For example, a 4:3 ratio means the picture is 4 units wide by 3 units high. It can also be written 4x3.
Note that the actual physical size of the picture is irrelevant.
Aspect Ratio refers only to the relationship between width and height. Common Aspect Ratios
There are three common aspect ratios:
4:3
This is the standard television format used throughout the second half of the 20th Century. Sometimes referred to as 12x9.
16:9
This format has gained acceptance as the new standard for widescreen TV, DVD and high-definition video
21:9 (Cinemascope)
A very wide screen format used for theatrical release movies.
Adapting the Ratio
Letterbox
Letterboxing is a technique used to display widescreen content on a traditional 4:3 screen such as those used by old-style television sets.
The technique is very simple — the picture frame is reduced in size until it fits the screen, leaving black bars above and below the picture.
The effect is like looking through the slot of a letterbox, hence the name. Pixel Issues
The information of a 4:3 or 16:9 aspect ratio is imbedded within the formatting of the program.
A device that does not correct for aspect will either display an image that is stretched out too wide, or narrowed and elongated.
| 
