Letterboxing
A technique for displaying movies on video in the original aspect ratio of the theater,
resulting in the apparent cropping of the top and bottom of the screen. The technique
accommodates program material that has a wide picture aspect ratio.
Level
A defined set of constraints on the values that may be taken by some parameters within
a profile. A profile can contain one or more levels.
LOCAL BUS
A data bus that connects directly, or almost directly, to the microprocessor. Although
local buses can support only a few devices, they provide very fast throughput. Modern PCs
include both a PCI local bus and a more general ISA expansion bus for devices that do not
require such fast data throughput. Lossless compression
A compression technique that preserves all the original information in an image or
other data structures.
Lossy compression
A compression technique that achieves optimal data reduction by discarding redundant
and unnecessary information in an image. See DCT.
Low Memory
In DOS systems, the first 640K of memory. This portion of memory is reserved for
applications, device drivers, and memory-resident programs (TSRs). Low memory is also
called conventional memory.
Low Voltage Differential (LVD)
Low voltage differential increases the bus cable length to 12 meters and provides the
capability to connect up to 15 peripherals on a single 16-bit SCSI bus.
LSI
Large Scale Integration; generally more than 1,000 and less than 10,000 components on
a computer chip.
Luma (Y)
One of the coefficients in composite video. Video originates with linear-light
(tristimulus) RGB primary components, conventionally contained in the range 0 (black) to
+1 (white). From the RGB triple, three gamma-corrected primary signals are computed; each
is essentially the 0.45-power of the corresponding tristimulus value, similar to a
square-root function.
Although television primaries have changed over the years since the adoption of the NTSC
standard in 1953, the coefficients of the luma equation for 525- and 625-line video have
remained unchanged. For HDTV, the primaries are different, and the luma coefficients have
been standardized with somewhat different values. |
