824 Chapter 28
28.8 Digital Video .........................................................................................................
In order to see the forces that have led to the rapid adoption of digital video processing
and interfacing throughout the television industry in the 1990s, it is necessary to look
at some of the technical innovations in television during the late 1970s and early 1980s.
The NTSC and PAL television systems described earlier were developed primarily
as transmission standards, not as television production standards. As we have seen,
because of the nature of the NTSC and PAL signal, high-frequency luminance detail
can easily translate to erroneous color information. In fact, this cross-color effect is an
almost constant feature of the broadcast standard television pictures and results in a
general “ business ” to the picture at all times. That said, these composite TV standards
(so named because the color and luminance information travel in a composite form)
became the primary production standard mainly due to the inordinate cost of “ three-
level ” signal processing equipment (i.e., routing switchers, mixers), which operated on
the red, green, and blue or luminance and color-difference signals separately. A further
consideration, beyond cost, was that it remained diffi cult to keep the gain, DC offsets,
and frequency response (and therefore delay) of such systems constant, or at least
consistent, over relatively long periods of time. Systems that did treat the R, G, and B
components separately suffered particularly from color shifts throughout the duration of
a program. Nevertheless, as analogue technology improved, with the use of integrated
circuits as opposed to discrete semiconductor circuits, manufacturers started to produce
three-channel, component television equipment that processed the luminance, R Y and
B Y signals separately. Pressure for this extra quality came particularly from graphics
areas, which found that working with the composite standards resulted in poor quality
images that were tiring to work on, and where they wished to use both fi ne detail textures,
which created cross-color, and heavily saturated colors, which do not produce well on a
composite system (especially NTSC).
So-called analogue component television equipment had a relatively short stay in the
world of high-end production largely because the problems of intercomponent levels,
drift, and frequency response were never ultimately solved. A digital system, of course,
has no such problems. Noise, amplitude response with respect to frequency, and time
are immutable parameters “ designed into ” the equipment—not parameters that shift
as currents change by fractions of milliamps in a base-emitter junction somewhere!
From the start, digital television offered the only real alternative to analogue composite
processing and, as production houses were becoming dissatisfi ed with the production