A little theory won't kill anybody...
Let us explain some of the basic terms connected to theory of reception usage of HD signal.
HDTV is abbreviation for
High Definition Television
. It involves a digital signal with higher picture
resolution than recent SDTV (
standard-definition television
) PAL, SECAM a NTSC standards.
Minimum HDTV resolution must be at least 720p (1280x720) – “720” means that the signal is
recounted on the TV screen in 720 horizontal lines and “p” means progressive (uninterlaced) mode.
An even higher quality image is reached with 1080i and 1080p (i = interlaced).
We can also encounter 576p - EDTV (Extended Television) version of resolution that is used by some
DVD players but is not used in satellite transmission
You can see comparison of different resolutions on Pic.1.
There are two ways of recounting picture used in practice -
progressive
and
interlaced
. In progressive
recounting just pair or impair lines are drown at the moment but the recounting progresses so quickly
that the human eye is not able to notice it in normal conditions. A small decrease of picture quality can
be seen during fast action scenes when noticeable flickering can appear. In interlaced recounting
whole screen (all lines) are drown at each moment - „refresh“.
To complete definition of HDTV signal we must describe information about number of pictures
(frames) displayed per one second. The designation of 720p signal should be for example 720p50 – it
means that the picture consists of 1280 x 720 pixels and is recounted 50 times a second. 1080p
resolution signal can be distributed in 1080p24, 1080p25 or 1080p30 (for NTSC) versions.
It is very important to realize the difference between picture quality of SDTV and HDTV. The new
generation of TV transmission enables up to four times higher resolution than SDTV, which results in a
sharper, more precise and more realistic picture.
Pic.1
