3. Vertical interval reference (VIR) signal. The VIR signal is a program-related
reference signal inserted during the vertical blanking interval of a color
television program.
It is intended to reduce undesirable variations in color
throughout the television system by assisting television producers, technicians,
and operators in adjusting various signal parameters so that different programs and
program segments have similar amplitude and phase characteristics whether viewed
sequentially on the same channel or on different channels.
a. The VIR signal is also intended to be associated with televised programs as
an operational tool for checking the parameters of the programs and is a reference
for the programs being transmitted.
The VIR signal, however, is not intended to
provide quantitative data on transmission distortions.
b. Because the VIR signal is intended to be associated with a particular
program, it should only be inserted into the program signal at a point in the video
system where both the correct amplitudes and phase of the composite color signal
are established and the artistic judgement is made that color reproduction is as
desired.
Thus, it is the responsibility of each production organization to make
that artistic judgement.
(1) Once
the VIR signal is inserted in this manner, it represents a
certification
of and a reference for the program signal. After the VIR signal has
been inserted
into the program signal, it must be treated exactly like the program
signal in all
equipment through which it passes so that the VIR signal will always
correspond to
the program.
(2) Then, when adjustments are made to restore a VIR signal to its proper
characteristics at any point in the video system, the program will have been re-
established to essentially the same characteristics as when it was initially
certified.
(3) The VIR signal inserted at the point of certification should remain with
the program to its final destination. Exceptions to this practice should be made
only at a point of recertification, such as an assembly point of various program
segments.
c. One important application of the VIR signal is in the adjustment of a
reproduced video tape recording. This usage applies to all video tape formats used
for broadcasting and is important both for the playback of a single tape and the
sequential playback of several short commercial program segments.
The VIR signal
will be added to each video tape at a point prior to the duplication of the final
release copies.
This will be done after the correct signal parameters are
established and any necessary artistic judgements have been made as to proper color
reproduction. The program then will have been certified.
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