Page 299 - Electrical Engineering Dictionary

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