DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Transcoding 1. Traditionally, converting a video signal having one colorencoding
method into a signal having a different color-encoding
method, without altering the scanning standard; for example,
576i PAL to 576i SECAM.
2. In compressed digital video distribution, various methods of
recoding a compressed bitstream, or decompressing then recompressing.
Transition sample An active sample near the left or right edge of the picture whose
amplitude is reduced or forced to blanking level so as to limit the
high-frequency content of the video signal at the picture edges.
Trichromaticity The property of human vision whereby additive mixtures of
exactly three properly chosen primary components are necessary
and sufficient to match a wide range of colors. That this is
possible is surprising, considering that physical spectra are infinitely
variable; but not surprising, considering that the retina
contains just three types of photoreceptor cone cells.
Trilevel sync Sync information conveyed through an analog pulse having
a transition from blanking level to +300 mV, then a transition
from +300 mV to -300 mV, then a final transition back to
blanking level. Standard for HDTV. Distinguished from bilevel sync,
used in SDTV.
Tristimulus A component value that represents spectral radiance weighted by
a spectral sensitivity function having significance with respect to
the trichromaticity of human vision (see Trichromaticity, above). In
video, a tristimulus signal such as R, G, or B is proportional to
intensity. RGB signals are subject to gamma correction as part of
their conversion into video signals.
TRS Timing reference signal: A sequence of four words that signals
sync, inserted into 4:2:2 or 4f SC data stream. See EAV, on
page 627, and SAV, on page 646.
TV lines per picture height,
TVL/PH
In video, a unit of horizontal resolution defined by the ratio of the
distance between spatially adjacent scan lines in the frame (as
numerator) and the picture height (as denominator). In an interlaced
system, adjacent scan lines are in opposite fields. One TV
line corresponds to a pixel, half a cycle, or half a line pair in film.
See Resolution (n.), on page 644.
U, V 1. Color difference components, blue minus luma (B’-Y’) and red
minus luma (R’-Y’), scaled prior to quadrature modulation by the
factors 0.492111 and 0.877283, respectively, to contain the reference
excursion of the composite video signal within the range
-33 1 ⁄3 IRE to +133 1 ⁄3 IRE. See also [C B , C R ]; [I, Q]; [P B , P R ].
2. The symbols U and V are sometimes used loosely or incorrectly
to refer to unscaled B’-Y’ and R’-Y’ components; to components
C B and C R that are scaled for component digital transmission; to
components P B and P R that are scaled for component analog
GLOSSARY OF VIDEO SIGNAL TERMS 649