Video distribution in many buildings is simply a retransmission of program-
ming provided by the local cable company. More sophisticated systems may
selectively filter or block some of the programming from a local cable com-
pany or insert local sources of video from a DVD, camera, data network or
character generator.
Video distribution, like other technology systems in a building has evolved
and is moving to digital formats, standard cable infrastructure (unshielded
twisted-pair copper and fiber optic cabling) and the IP protocol. The result
is IP television or IPTV. In many ways video distribution is following the evo-
lutionary technical path that voice, wireless, video surveillance and access
control have taken.
Video Display and Viewing
In 1941 the U.S. National Television Standards Committee (NTSC) proposed
the original analog television format for black and white television, following
in 1950 with a backward compatible standard for color television. Many of
us still watch television in the 1950 standard.
Analog video is a group of still images or frames. Thirty of these frames are
broadcast each second giving viewers a visual sense of motion. The quality of
the resolution of any video transmission is determined by the number of horizon-
tal lines displayed on the screen and the number of tiny dots, or pixels, that emit
either red, blue, or green light to create the picture we see on the screen. The total
number of pixels is the measure of the quality or resolution of the picture.
The 1941 analog standard called for 480 horizontal lines of resolution (addi-
tional lines are reserved for synchronization and information such as captioning),
720 pixels per horizontal line, and a technique called interlacing. Interlacing
means that only half of the horizontal lines are used in creating each frame; that
is, even-number lines are broadcast in one frame and odd number horizontal lines
are broadcast in the next frame. The total resolution of a screen can be calculated
by multiplying the number of pixels in each line by the number of lines on the
screen (720 pixels per horizontal line for 480 lines¼345,600 total pixels).
There are currently 18 different digital television formats set by the
Advanced Television System Committee (ATSC) standard. These are formats
for televisions and displays that can be grouped as follows:
Standard Definition (SDTV)—This is basically the analog television standard
delivered as a digital signal with three variations of the formats dealing with
the number of pixels, the shape of the pixels, and use of interlacing.
Enhanced Definition (EDTV)—EDTV is like SDTV with the main difference
being that it uses progressive scanning rather than interlacing. There are
Video, IPTV, and Digital Signage Systems 93