High Definition

High Definition (HD) refers to the
resolution that a television is able to display. The image on your
television is made up of many small dots, called pixels. Standard
Definition, which is the TV that you watched growing up, comes in at a
resolution of 480 pixels from top to bottom and 640 pixels from left to
right. High definition, as the name suggests, increases the number of
pixels that form the image.

The terms used to describe high definition refer specifically to the
number of lines on pixels that can be displayed from top to bottom. The
different formats of high definition TV signal are known as 720p, 1080i
and 1080p. The first refers to content with 720 lines from top to
bottom and the latter two to content that has 1080 lines from top to
bottom. The “p” and “i” refer to progressive scan and interlaced scan
respectively, see our article on 1080p for a more in-depth discussion of the difference between progressive and interlaced.

The High Definition standard also defines the aspect ratio of the
content. In order to be considered high definition the content must
have an aspect ratio of at least 16:9, which is generally referred to
as widescreen content. As such any High Definition content will be
widescreen. The High Definition standard also supports even wider
aspect ratios, but none that are more narrow. TV shows filmed in the
4:3 aspect used in standard definition TV can either be stretched to
fit the screen, or presented with two black bars on the side to fill
out the screen. Currently both content and displays max out at 1080p,
however more High Definition standards with even higher resolutions are
being worked on. The next expected resolution of high definition will
be 2160p, which has a resolution of 2160 lines from top to bottom and
3840 lines from left to right in standard 16:9 aspect ratio. The
Japanese have also been experimenting with a format called Super
Hi-Vision, which has a resolution of 7680 by 4320 pixels. This next
iteration of HD is not expected to be commercially available for some
years yet.

Another commonly used phrase with HDTVs is Full HD. Although this
phrase does not have a formal definition, it usually refers to a
display that has enough pixels to represent every pixel of a 1080p
signal. The majority of medium and high-end LCD and Plasma HDTVs on the
market at the moment are Full HD models, but some rear projection and
low-end models claim to be 1080p, but do not have enough pixels to
represent every pixel in the signal. There are also still some
lower-end models that support a maximum resolution of 720p, although
these can generally downsample higher resolution content to fit on the
screen.