DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

K-factor, K-rating A numerical characterization of pulse fidelity, obtained by
measuring the tightest fit of a specific set of time-domain envelope
to a raised cosine test pulse. Distinguished from Kell factor, k
below.
Kell effect In a video system – including sensor, signal processing, and
display – Kell effect refers to the loss of resolution, compared to
the Nyquist limit, caused by the spatial dispersion of light power.
Some dispersion is necessary to avoid aliasing upon capture, and
to avoid objectionable scan line (or pixel) structure at display.
Kell factor, k Historically, the ratio between effective resolution and theoretically
obtainable resolution for a given number of active scan lines.
Generally between 0.7 and 0.9. Now deprecated. Distinguished
from interlace factor; also distinguished from K-factor, K-rating.
Key A component signal indicating transparency of the accompanying
foreground image data, coded between zero (fully transparent)
and unity (fully opaque). In computer graphics, called alpha, α
(see page 613). The keying (or compositing) operation is
performed as: R = α · FG +(1-α)·BG, where FG represents foreground
(fill) video and BG represents background video. Foreground
image data that has been premultiplied by the key is
called shaped in video (or associated or premultiplied in computer
graphics). Foreground image data that has not been premultiplied
by the key is called unshaped in video (or unassociated or nonpremultiplied
in computer graphics).
L A , active lines The count of scan lines containing the picture. L A for a frame is
equivalent to the number of rows of image samples. (Vertical
interval lines are not considered active; however, closed caption
lines in 480i are considered active.)
L T , total lines The count of total scan lines in a frame.
Legal 1. In component video signal coding, the condition where each
signal of a component set lies within its reference range. In an
R’G’B’-legal combination, all of R’, G’, and B’ lie within their reference
ranges. (See also Valid, on page 650.)
2. In NTSC and PAL coding and transmission, compliance with
broadcast standards. (NTSC broadcast transmission has a 120 IRE
amplitude limit that requires limiting the saturation of colors near
pure yellow and pure cyan.)
3. In JPEG or MPEG, a bitstream that is compliant with standards,
an encoder that produces only compliant bitstreams, or a decoder
that correctly decodes any compliant bitstream.
Letterbox A widescreen image (such as 16:9 aspect ratio) conveyed or
presented in a format having a narrower aspect ratio (such as 4:3),
using the full width of the narrower format but not using the full
height.
634 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES