The aspect ratio of an image is ratio of the displayed width to the height of the image (usually expressed as "x:y"). For instance, the aspect ratio of a traditional television screen is 4:3, or 1.33:1. A high definition television uses an aspect ratio of 16:9, or about 1.78:1.
Televisions now come in 2 different shapes:
- Standard Definition Television: This is the traditional television set that has appeared in homes for the past 50 years. A standard definition television set, also called NTSC, has a resolution of 480i and is in a 4:3 aspect ratio. Also called NTSC.
- High Definition Television: The latest television that will be in all homes soon. A high definition television has a max resolution of 1080i/p and is in a 16:9 aspect ratio.
When trying to fit a 16:9 film on a standard definition TV, black bars are added to the top and bottom of the film in order to preserve the director's composition and original theatrical experience. This process is called Letterbox.
WIKIPEDIA ARTICLE ON ASPECT RATIOS
What to learn more? Check out this article from CinemaSource (Adobe pdf format file)
