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Video Standards -
NTSC - is the analog television system in use in Canada, Japan, South
Korea, the Philippines, the United States and a few other countries in the
Americas. It is named for the National Television System(s) Committee,
the U.S. standardization body that adopted it. In 1941 the committee
settled on a 525-line transmission standard, with a frame rate of 30 frames
per second, with an aspect ratio of 4:3, which is still basically the United
States Standard to this day. The NTSC format is used with the M format
which consists of 29.97 interlaced frames of video per second. Each frame
consists of 484 lines out of a total of 525 (the rest are used for sync,
vertical retrace, and other data such as captioning). The NTSC refresh
frequency was originally exactly 60 Hz in the black and white system,
chosen because it matched the nominal 60 Hz frequency of alternating
current power used in the United States
PAL – short for phase-alternating line, phase alternation by line or phase
alternation line, is a color encoding system used in large parts of the
world, predominantly in Europe (except France which uses SECAM).
PAL uses 625 lines, and a 50 Hz refresh rate, (which recently has been
changed to 100 Hz to reduce flicker rate). [Hertz (Hz), stands for cycles
per second] This gives a better quality and more stable picture. PAL
format as it has greater resolution than NTSC, is generally better than the
latter, especially for DVD movies. However, the alternation of color
information - Hanover Bars - can lead to picture grain on pictures with
extreme phase errors even in PAL systems
SECAM – also written SÉCAM (Séquentiel couleur à mémoire, French for
"sequential color with memory"), is an analog color television system first
used in France. It is similar to PAL, it also uses 625 lines and a 50 Hz
system. As color television became popular, there was a requirement that
monochromatic (black and white) television sets remain compatible.
Because of the requirement, color standards add a second signal to the
basic monochrome signal, and this signal carries the color information,
called chrominance (or C in short), while the black and white information
is called the luminance (Y in short). Old TV receivers only see the
luminance, while color receivers process both signals. In order to get
color, and not increase bandwidth, the color signal has to be somehow
inserted into the monochrome signal, without disturbing it. This insertion
is possible because the spectrum of the monochrome TV signal is not
continuous, hence empty space exists which can be utilized. This lack of
continuity results from the discrete nature of the signal, which is divided
into frames and lines. Analogue color systems differ by the way in which
empty space is used. In all cases, the color signal is inserted at the end of
the spectrum of the monochrome signal. The color space is three
dimensional by the nature of the human vision, so after subtracting the
luminance, which is carried by the base signal, the color sub carrier still
has to carry a two dimensional signal. Typically the red (R) and the blue
(B) information are carried because their signal difference with luminance
(11 Seiten)
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