This refers to the picture's screen format or shape. The ratio of a screen's width to its height is called the aspect ratio. When you see the words "THIS FILM HAS BEEN FORMATTED TO FIT YOUR TV" this means that the widescreen image from the original movie has been chopped or modified to fit your square television at home. Analog televisions typically have an aspect ratio of 4:3 (pronounced 4 by 3), in other words, if a television is three inches high, it has to be four inches wide to display today's analog signal. 4 parts wide by 3 parts high.
The new digital standard supports a wider screen, with an aspect ratio of 16:9. (or 16 parts wide by 9 parts high) reminiscent of the widescreens found in the theater. The ATSC standard supports both of these picture shapes.
Many digital televisions and all HDTV's will support a wider, more cinematic screen shape to enable you to see the whole picture in the wide format in which it was filmed.
Not all HDTV's will be in a 16:9 format, some will be the traditional 4:3 shape. In order to qualify as a High Definition Television, a set must be able to display a 16:9 format and reproduce at least 1 million pixels. To display a widescreen image on a square TV, manufacturers will often "Letterbox" or shrink the image until it fits on the screen, then the top and bottom of the screen are filled in with dark bands. As a rule of thumb, if a television set can display a one-million pixel count, it can be classified as a HDTV. Pixel count can be determined by multiplying the horizontal lines of resolution by the vertical lines.
What are the different Resolution Standards?
SDTV can be either 480i or 480p (the p stands for progressive) and will most likely be in a 4:3 aspect ratio.
HDTV signals, on the other hand, will be 720p, 1080i or 1080p and will be presented in a 16:9 ratio.