Page 86 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes explained that the 16 : 9 ratio was chosen as being the geometric mean of 4 : 3, Academy ratio,
and 2.4 : 1, the widest cinema format in common use, in order to minimize wasted screen space
when displaying content with a variety of aspect ratios.)
An aspect ratio of 16 : 9 was duly agreed at the first meeting of the IWP11/6 working party
at the BBC’s Research and Development establishment in Kingswood Warren. The resulting
ITU-R Recommendation ITU-R BT.709-2 (“Rec. 709”) includes the 16 : 9 aspect ratio, a specified
colorimetry, and the scan modes 1080i (1,080 actively interlaced lines of resolution) and 1080p
(1,080 progressively scanned lines). The British Freeview HD trials used MBAFF, which contains
both progressive and interlaced content in the same encoding.

5.3 analogue video

The original video recording method that stores continuous waves of red, green and blue
intensities. In analogue video, the number of rows is fixed. There are no real columns and the
maximum detail is determined by the frequency response of the analogue system.
Analogue video may be carried in separate channels, as in two channel S-Video (YC) and multi-
channel component video formats.
Analogue video is used in both consumer and professional television production applications.
However, digital video signal formats with higher quality have been adopted, including serial
digital interface (SDI), Firewire (IEEE1394), Digital Visual Interface (DVI) and High-definition
Multimedia Interface (HDMI).

5.3.1 analogue video formats
Composite video signals are analogue signals that combine luminance and chrominance (colour)
information in a single analogue signal that can be transmitted over a single wire or stored in a
single track on an analogue magnetic tape. The NTSC video signals used by commercial television
sets in the US and Japan are an example of composite signals. Composite video is particularly
prone to errors in reproducing exact colours due to the overlap of the colour and luminance
signals. Video professionals jokingly refer to “Never The Same Colour” (NTSC).
The S-Video signals separate the luminance and chrominance information into two separate
analogue signals that can be transmitted over two separate wires or stored in two separate tracks
on an analogue tape. The S-Video is generally superior to composite video in reproducing colours
correctly. The S-VHS and Hi8 video tape standards use S-Video. Ordinary VHS video tape uses
composite NTSC signals. Thus, in general, using an S-VHS or Hi8 video camera with S-Video
output to provide the analogue video signal to the S-Video input of a PC video capture card will
provide better video quality.
A third type of video signal is component video. In component video, the luminance (Y) and
two colour difference signals (U and V or I and Q) are separated into three separate analogue
signals that can be transmitted over three separate wires or stored in three separate tracks on an
analogue tape, or digitized separately. Component video is used in professional video production
and provides the best quality and the most accurate reproduction of colours. The professional
Betacam SP video cameras use component video. The current generation of widely used PC video
capture cards do not provide component video inputs.

5.4 Digital video

Digital video is audio/visual in a binary format. Information is presented as a sequence of digital
data, rather than in a continuous signal as analogue information is.
Information in the natural world, received through the five senses, is analogue. That means it is
infinitely variable. Digital A/V information, on the other hand, consists of discrete units of data that

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