DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

PAL, nonmathematical A PAL (1) system, with 576i scanning, wherein the unmodulated
color subcarrier is incoherent with sync or the +25 Hz offset is
absent. See PAL, mathematical, above.
P B , P R
Scaled color difference components, blue and red, used in component
analog video: Versions of B’ minus luma (B’-Y’) and R’ minus
luma (R’-Y’) scaled for excursion nominally identical to luma for
component analog transmission. P B and P R according to the
EBU N10 standard are equivalent to C B and C R scaled by the
factor 219 ⁄224; however, various different industry standards are in
wide use for 480i. See also C B, C R, on page 616, and U, V, on
page 649.
Peak white The most positive excursion of a luma, R’, G’, or B’ component.
Distinguished from reference white: Reference white is usually not
“peak,” because studio video systems typically allow signals to
excurse to a peak somewhat above the reference white level.
Pedestal Black level (see page 614) expressed as an offset in voltage or IRE
units relative to blanking level. Conventionally about 54 mV (7.5
IRE) in ITU-R System M, SMPTE 170M, and the archaic EIA
RS-343-A; conventionally zero in all other systems, where
blanking level and black level are identical. Pedestal is properly
a voltage offset or a level; it is incorrect to express pedestal as
a percentage. See also Setup, on page 647.
Picture In MPEG-2, one of (i) a top field, (ii) a bottom field, or
(iii) a progressive frame.
Picture excursion The excursion from blanking to reference white. In 480i, 100 IRE
by definition. In analog System M and the archaic EIA RS-343-A,
5 ⁄7 V (about 714 mV); in other systems, particularly 576i and
HDTV, 700 mV.
Picture:sync ratio The ratio between picture excursion (from blanking to reference
white) and sync excursion (from synctip to blanking). Conventionally
10:4 for System M and the archaic EIA RS-343-A, and 7:3 in
other systems.
Pillarbox format An image (such as 4:3 aspect ratio) conveyed or presented in
a format having a wider aspect ratio (such as 16:9), using the full
height of the widescreen format but not using the full width. The
term echoes letterbox; it derives from the name for a tall postbox
in the U.K.
Pixel Picture element: The collection of quantized samples that are
specific to a single spatial sampling site in an image; usually three
color component samples, perhaps augmented by a transparency
(alpha or key) component sample. The term is ambiguous when
chroma subsampling is involved.
Power function A function of the form y = x a (where a is constant). Distinguished
from exponential function, which has the form y = a x (where a is
constant). Gamma correction in video approximates a power function
V’ = L γ E, where γ E (the encoding gamma) symbolizes a
GLOSSARY OF VIDEO SIGNAL TERMS 641