Electrical Engineering Dictionary - part 88

(2) the place from which input and out-

put occurs in a computer. Examples include
printer port, serial port, and SCSI port.

I/O processor

an input/output processor

with a unique instruction set, dedicated to
performing I/O operations exclusively, thus
alleviating the burden off the CPU. It usually
has a separate local bus for I/O operations
data traffic, thus permitting the CPU to ac-
cess memory on the main system bus with-
out interruption. For example, the Intel 8086
CPU has an 8089 I/O processor associated
with it. Both can operate simultaneously, in
parallel.

I/O register

a special storage location

used specifically for communicating with in-
put/output devices.

I/O routine

a function responsible for

handling I/O and transferring data between
the memory and an I/O device. See also

I/O

controller

I/O system

the entire set of input/output

constructs, including the I/O devices, device
drivers, and the I/O bus.

I/O throughput

the rate of data trans-

fer between a computer system and I/O de-
vices. Mainly determined by the speed of the
I/O bus or channel. Throughput is typically
measured in bits/second or bytes/second. In
some instances, the throughput average rate
is given and in others the maximum rate is
given. See also

I/O bandwidth

I/O trunk

See

I/O bus

I/O unit

the equipment and controls nec-

essary for a computer to interact with a hu-
man operator or to access mass storage de-
vices or to communicate with other computer
systems over communication facilities.

I-line

a line of the mercury spectrum cor-

responding to a wavelength of about 365 nm.

See

index assignment

IAEA

International Atomic Energy Agency,

an organization which monitors nuclear ma-
terials and energy.

See

integrated circuit

ICE

See

in-circuit emulator

ideal filter

(1) a system that completely

rejects sinusoidal inputs of the form

x(t)4 =

A cos ωt, −∞ < t < ∞, for ω within a cer-
tain frequency range, and does not attenuate
sinusoidal inputs whose frequencies are out-
side this range. There are four basic types of
ideal filters: low-pass, high-pass, band-pass,
and bandstop.

(2) a filter that has zero gain in the stop-

band, a constant, usually unity, gain in the
passband, and a zero transition band width. A
1-D ideal lowpass filter has unity gain for fre-
quencies less than or equal to the cutoff fre-
quency, and zero gain for frequencies greater
than the cutoff frequency. An ideal filter is
unrealizable in practice.

ideal operating amplifier

an op amp hav-

ing infinite gain from input to output, with
infinite input resistance and zero output re-
sistance and insensitive to the frequency of
the signal. An ideal op amp is useful in first-
order analysis of circuits.

ideal transformer

a transformer with zero

winding resistance and a lossless, infinite
permeability core resulting in a transformer
efficiency of 100 percent. Infinite permeabil-
ity would result in zero exciting current and
no leakage flux. For an ideal transformer, the
ratio of the voltages on the primary and sec-
ondary sides would be exactly the same as
the ratio of turns in the windings, while the
ratio of currents would be the inverse of the
turns ratio.

ideality factor

the factor determining the

deviation from the ideal diode characteristic
m = 1. At small and large currents m ≈ 2.

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idempotent

an operator is idempotent if

applying it twice gives the same result as ap-
plying it only once; mathematically speak-
ing, if

ψ is the operator and X the ob-

ject to which it is applied, this means that
ψ(ψ(X)) = ψ(X).

idler wave

the additional, often unwanted,

output wave produced by an optical paramet-
ric oscillator designed to generate a signal
wave.

IEC

See

International Electro-technical

Commission

IEEE

See

Institute of Electrical and

Electronics Engineers

IEEE Color Books

a series of seven

books related to industrial and commer-
cial power systems containing recommended
IEEE/ANSI standards and practices.

The

books are color-coded as to subject as fol-
lows:

Gray:

Power systems in commercial

buildings

Green: Grounding industrial and com-

mercial power systems

Brown: Power system analysis
Gold: Design of reliable industrial and

commercial power systems

Orange: Emergency and standby power

for industrial and commercial power systems

Red: Electric distribution practice in in-

dustrial plants

Buff: Protection and coordination of in-

dustrial and commercial power systems.

IEEE float encoding

See

NaN

IEEE representation

an encoding con-

vention for the representation of floating-
point values within computing systems.

IEEE Standard 754

the specification that

defines a standard set of formats for the rep-
resentation of floating-point numbers.

See

intermediate frequency

IF amplifier

an amplifier having high

and controllable gain with a sharp band-pass
characteristic centered around the intermedi-
ate frequency (IF).

IGBT

See

insulated gate bipolar junction

transistor

ignitron

a high-voltage mercury switch.

The device is found in modulators used to
dump the capacitor bank voltage in the event
of a PA crowbar. An ignitron passes electrical
current to a pool of liquid mercury at ground
potential.

II-VI semiconductor

binary semicon-

ductor made from elements in the periodic
table two columns to the “left” and “right” of
silicon, e.g., CdTe, ZnS, etc.

IID

See

independent and identically

distributed

III-V semiconductor

a binary semicon-

ductor made from elements from columns III
and V in the periodic table.

illumination

(1) in vision science, the

amount of light per unit area delivered to a
surface and accounting for the spectral sen-
sitivity of the human eye.

(2) informally, the amount of light falling

on an object. Also called illuminance. See
also

luminance

(3) the effect of a visible radiation flux

received on a given surface. Illumination is
measured by the illuminance, which is the lu-
minous flux received by surface unit, usually
expressed in lux. One lux equals 1 lumen/m

illumination system

the light source and

optical system designed to illuminate the
mask for the purpose of forming an image
on the wafer.

ill-posed problem

a problem whose so-

lution may not exist, may not be unique, or
may depend discontinuously on the data. (A
problem is well-posed if it can be shown that

2000 by CRC Press LLC

its solution exists, is unique, and varies con-
tinuously with perturbation of the data. If
any of the three conditions does not hold, the
problem is ill-posed.)

image

information stored digitally in a

computer, often representing a natural scene
or other physical phenomenon, and presented
as a picture. The brightness at each spot in
the picture is represented by a number. The
numbers may be stored explicitly as pixels or
implicitly in the form of equations. See also

ie s

image acquisition

the conversion of

information into an image.

Acquisition

is the first stage of an image processing
system and involves converting the input
signal into a more amenable form (such
as an electrical signal), and sampling and
quantizing this signal to produce the pix-
els in the image.

Hardware, such as

lenses, sensors and transducers are partic-
ularly important in image acquisition. See
also

analog-to-digital converter

image analysis

the extraction of infor-

mation from an image by a computer. The
results are usually numerical rather than pic-
torial and the information is often complex,
typically including the recognition and inter-
pretation of objects in or features of the im-
age.

image classification

the division by a

computer of objects in an image into classes
or groups. Each class contains objects with
similar features. Also, the division of the
images themselves into groups according to
content.

image coding

the usual reasons for coding

messages lie in the areas of data compres-
sion and data security. However, the main
motivation for recoding images is to achieve
the high rates of data compression required

to cope with the storage and transmission of
prodigious amounts of image data. See

still

image coding

and

video codingfor methods.

image coding for videoconferencing

this

is also called coding at primary rates for
videoconferencing. In North America and
Japan, one of the most plentiful is the DSI rate
of 1.544 Mb/s. In Europe, the corresponding
rate is 2.044 Mb/s. The main difference is
that in videoconferencing the video camera
is fixed and picture data is produced only if
there are moving objects in the scene. Typ-
ically, the amount of moving data is much
smaller than the stationary area.

image compression

representation of still

and moving images using fewer bits than
the original representation. See

still image

coding

and

video coding

for methods.

image compression or coding

the pro-

cess of reducing the number of binary digits
or bits required to represent the image.

image correlation

the calculation of the

correlation function where the two signal in-
puts are images.

image degradation

blurring of an image

wavefront due to scattering as it passes an
inhomogeneous medium, e.g., astronomical
images due to atmospheric scattering.

image dissector

a nonstorage photoemis-

sion device used as a light detector in early
television camera tubes. Electron streams,
emitted by light striking a photocathode
film, are focused on a plane containing a
small aperture into a photomultiplier struc-
ture. Scanning is accomplished by magneti-
cally deflecting the electron stream across the
aperture.

image enhanced mixer

mixer that op-

erates on the principle of terminating the
image frequency component at an optimal
impedance level that improves the conversion

2000 by CRC Press LLC

loss of the mixer. The optimal impedance ter-
mination allows the image product to remix
with the LO frequency component such that
the down-converted signal is in phase with
the IF component and thus increases its mag-
nitude. The image spectral component is at a
frequency that is either the sum or difference
of the LO and IF components.

image enhancement

processing an image

to improve its appearance, or to make it more
suited to human or machine analysis. En-
hancement is based not on a model of degra-
dation (for which, See

restoration

) but on

qualitative or subjective goals such as remov-
ing noise and increasing sharpness. Contrast
stretching, edge emphasis, and smoothing are
examples of enhancement techniques.

image feature

an attribute of a block of

image pixels.

image frequency rejection ratio

ratio of

output for the image frequency below that
for the desired signal when both image and
desired signal levels at the input are the same.

image frequency response

output gener-

ated in a superheterodyne receiver due to an
undesired signal with a frequency spaced by
twice the IF from desired frequency.

image fusion

the merger of images taken

with different imaging modalities or with dif-
ferent types of the same modality, for ex-
ample, different spectral bands.

See also

multispectral image

image guide

a type of dielectric waveg-

uide based on a dielectric rod waveguide with
a conducting plate placed at the plane of sym-
metry.

image hierarchy

a way to organize the

image data in order of importance.

Each

level corresponds to a reconstructed image
at a particular resolution or level of quality.
Generally, they are classified into fixed and
variable resolution hierarchies.

image impedance

the input impedance

into a passive 2-port device when that device
is terminated in an infinite chain of identi-
cal devices connected to both ports such that
each port is connected to the same port (i.e.,
port 1 connects to port 1 and port 2 connects
to port 2 throughout the infinite chain, giv-
ing a perfect match). The impedance looking
into port 1 is

I11

, and into port two is

I22

For a uniform transmission line, the image
impedances are equal to each other and also
equal to the characteristic impedance of the
line.

image processing

the manipulation of

digital images on a computer, usually done
automatically (solely by the computer) but
also semi-automatically (the computer with
the aid of a person). The goal of the pro-
cessing may include compressing the image,
making it look better, extracting information
or measurements from it or getting rid of
degradations.

See also

image recognition

the identification and

interpretation of objects in an image. Im-
age recognition is a higher-level process that
requires more intelligence than other parts
of image processing such as image enhance-
ment. Artificial intelligence, neural nets or
fuzzy logic are often used. See also

artificial

intelligence

artificial neural network

image reconstruction

(1) the process of