HDTV: An Advertising Myth De-bunked

There's a great deal of nonsense talked about HDTV and much of the noise comes
from manufacturers' and retailers' advertising which in some cases is extremely
misleading.

One of the areas of greatest confusion is resolution. Resolution is defined as the
number of pixels - the elements which make up a digital image - in an image and is
usually quoted as a x b, where a is the number of pixels across the screen
(horizontal) and b is the number of pixels up and down (vertical, also referred to as
the number of lines). In this article we'll explain everything you need to know about
the number of pixels required for HDTV.

HDTV Specification

HDTV: An Advertising Myth De-bunked

The HDTV specification provides for three different types of HDTV, denoted by the
number of lines of resolution and the signal type. They are:

1080p (1080 lines, progressive scan)

1080i (1080 lines, interlaced)

720p (720 pixels, progressive)

Any TV not capable of displaying at least 720 lines is not 'HDTV ready' and any
signal with fewer than 720 lines is not an HDTV signal.

Interlaced or Progressive?

The 'i' and 'p' in the HDTV specification refer to interlaced and progressive scan. The
analog TV we've been watching for years is interlaced. That simply means that each
frame of video (of which there are 30 per second in NTSC and 24 per second in PAL)
is split into two fields. Each field contains alternate lines of the signal (one has the
odd, the other the even) and is displayed for 1/60th of a second (1/48th for PAL).
Because it happens so fast, your brain interprets each frame as a single image.
Progressive scan signals have no fields, they simply display each frame in its
entirety for 1/30th (or 1/24th) of a second. This results in a higher quality image,
particularly noticeable in fast-action broadcasts such as sporting events.

So every TV that can display 720 lines is HDTV ready?

No, and this is one of the key areas of confusion. The other important element of
the HDTV specification is that signals must be broadcast in 16:9 widescreen. This is
known as the aspect ratio, where '16' refers to the width of the image and '9' to the
height. In other words, the height of the picture is 9/16ths of the width.
Some manufacturers promote TVs with a maximum resolution of 1024 x 768 pixels
as HDTV ready. This is incorrect. Although the total number of vertical pixels is
greater than the 720 minimum necessary for HDTV, at an aspect ratio of 16:9 it
would need 1280 pixels horizontally to display a 720-line HDTV picture. The only
solution is to either squash or crop the picture, neither of which is satisfactory.
So, in order to be properly HDTV capable, a TV needs to be able to display at least
1280 pixels horizontally as well as at least 720 vertically.

Remember before you buy to check that the resolution of your HDTV is at least
1280 x 720 pixels and don't rely on the logo on the box.

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