used in order to alleviate circuit losses at high
microwave frequencies.
spatial redundancy
the redundancy be-
tween samples of an image or random process
that is a function of spatial coordinates. Im-
ages typically exhibit a high degree of spatial
redundancy which can be exploited to obtain
a high compression ratio.
spatial resolution
(1) the ability to re-
solve two closely spaced points or a periodic
pattern. Rayleigh proposed the criterion that
two stars could be resolved when the maxi-
mum in the image pattern from one star co-
incides with the first minimum in the other.
Units of spatial resolution are lines or line
pairs per millimeter.
(2) a measure of the ability of a system
to resolve spatial details in a signal. For a
discrete image, spatial resolution generally
refers to the number of pixels per unit length,
giving possibly different horizontal and ver-
tical spatial resolutions. See also
frequency
resolution
.
spawn
to create a new process within a
multitasking computing system.
SPDT
See
single-pole double-throw
.
speaker identification
a task that consists
of identifying which speaker (of a closed set)
pronounced a given portion of speech signal.
The basic assumption is that no speaker dif-
ferent from the defined closed set is consid-
ered. The emphasis is on the discrimination
of the given speakers, whereas no strong re-
jection constraints are commonly required.
speaker verification
a task that, unlike
speaker identification, the speaker set for this
problem is open. As a consequence, one has
to verify the given speaker against any poten-
tional impostor that is not known in advance.
Basically, one cannot rely on the knowledge
of the probability distribution of the “nega-
tive examples,” since there is no restriction
on who is supposed to use the verification
system.
SPEC
See
System Performance and
Evaluation Cooperative
.
SPEC benchmarks
suites of test pro-
grams created by the System Performance
and Evaluation Cooperative.
special-purpose digital signal processor
digital signal processor with special feature
for handling a specific signal processing ap-
plication, such as FFT.
specific absorption rate (SAR)
the depo-
sition of energy over time into a body. The
units are generally watts per kilogram of body
mass. This is the attribute on which findings
by various researchers can be compared and
on which the exposure standards base their
guidelines.
specific inductive capacity
See
dielectric
constant
.
specification
a statement of the design or
development requirements to be satisfied by
a system or product.
speckle
(1) grainy light pattern that results
when coherent light scatters from a rough sur-
face.
(2) granular image noise due to fluctua-
tions in the number of photons arriving at an
image sensor. Speckle often occurs in night-
vision equipment and X-ray images. Also
called quantum mottle.
speckle pattern
grainy appearance of the
intensity of scattered light due to random in-
terference. The grain size is inverse of the
illuminated area of the scattering medium in
wavelength units.
SPECT
See
single photon emission
computed tomography
.
c
2000 by CRC Press LLC