classification describing any “motor built in
a frame smaller than that having a continuous
rating of 1 horsepower, open type, at 1700 to
1800 rpm.”
fractional rate loss
for frame-by-frame
transmitted convolutionally encoded data,
the fraction of overhead (compared to the size
of the frame) needed to put the encoder into
a known state.
fragmentation
waste of memory space
when allocating memory segments for pro-
cesses. Internal fragmentation occurs when
memory blocks are rounded up to fix block
sizes, e.g., allocated in sizes of power of 2
only. E.g., if 35 K of data is allocated a 64 K
block, the difference (64
− 35 = 29K) is
wasted. External fragmentation occurs be-
tween allocated segments, as a result of allo-
cating different sized segments for processes
entering and leaving memory.
This latter
fragmentation is also called checkerboard-
ing.
frame
(1) a set of four vectors giving po-
sition and orientation information.
(2) the basic element of a video sequence.
The standard frame rate for TV standards
is 25 frames/s (European standards, e.g.,
PAL and SECAM) or 30 frames/s (U.S. and
Japanese standards, e.g., NTSC).
(3) in paging systems, a memory block
whose size equals the size of a page. Frames
are allocated space according to aligned
boundaries, meaning that the last bits of the
address of the first location in the frame will
end with
n zeros (binary), where n is the ex-
ponent in the page size. Allocating frames
for pages makes it easy to translate addresses
and to choose a frame for an incoming page
(since all frames are equivalent).
(4) time interval in a communication sys-
tem over which the system performs some pe-
riodic function. Such functions can be mul-
tiple access functions (e.g., TDMA multi-
ple access frame) or speech-processing func-
tions (e.g., speech coding frame, interleaving
frame, or error control coding frame).
(5) single image; component of a se-
quence of images which, displayed rapidly
in succession, give the illusion of a moving
picture. In video a frame represents a single
complete scan of the image; it often consists
of two interlaced fields.
frame grabber
a device that is attached to
an electronic camera and which freezes and
stores images digitally, often in gray-scale or
color format, typically in one or three 8-bit
bytes per pixel respectively.
frame memory
video memory required
to store the number of picture elements for
one complete frame of electronically scanned
video information. The memory storage in
bits can be computed by multiplying the
number of video samples made per horizontal
line, times the number of horizontal lines per
field (vertical scan), times the number bits per
sample, times the number of fields/frame. A
sample consists of the information necessary
to reproduce the color information.
The NTSC television system consists of
two interlaced fields per frame. Storage re-
quirements are usually minimized by sam-
pling the color video information consisting
of the luminance (
Y ) and the two color differ-
ence signals, (
R −Y ) and (B −Y ). The color
signal bandwidth is less than the luminance
bandwidth that can be used to reduce the field
memory storage requirements. Four samples
of the luminance (
Y ) signal is combined with
two samples of the (
R − Y ) signal and two
samples of the (
B − Y ) signal. The preced-
ing video sampling techniques is designated
as 4:2:2 sampling and reduces the field mem-
ory size by one third.
The number of memory bits that are re-
quired to store one NTSC frame is two times
the number of bits required to store one
NTSC field. Field memory for NTSC video
sampled at 4 times the color subcarrier fre-
quency at 8 bits/pixel would require 7.644
megabits of RAM when 4:2:2 sampling is
used.
c
2000 by CRC Press LLC