connecting signals are given as Laplace trans-
formations. Although the system blocks and
signals have the same mathematical form, the
blocks represent operators that act on the in-
coming signals while the signals represent
functions of time.
block matching
the process of finding the
closest match between a block of samples in
a signal and a block of equal size in another
signal (or a different part of the same sig-
nal) over a certain search range. Closeness
is measured by correlation or an error metric
such as mean square error. Used in data com-
pression, motion estimation, vector quantiza-
tion, and template matching schemes.
block multiplexer channel
an I/O chan-
nel can be assigned to more than one data
transfer at a time. It always transfers infor-
mation in blocks, with the channel released
for competing transfers at the end of a block.
See also
byte multiplexer channel
,
selector
channel
.
block transfer
the transmission of a sig-
nificantly larger quantity of data than the min-
imum size an interconnect is capable of trans-
mitting, without sending the data as a number
of small independent transmissions (the goal
being to reduce arbitration and address over-
head).
block transform
a transform that divides
the image into several blocks and treats each
block as an independent image. The trans-
form is then applied to each block indepen-
dently. This occurs in the JPEG standard im-
age compression algorithm, where an image
is divided into 8
× 8 blocks and the DCT
is applied independently to each block. Usu-
ally the blocks do not overlap each other, that
is, they have no signal samples in common.
See also
transform coding
,
lapped orthogonal transform
.
block truncation coding (BTC)
tech-
nique whereby an image is segmented into
n × n nonoverlaping blocks of pixels, and
a two-level quantizer is designed for each
block. Encoding is essentially a local bina-
rization process consisting of a
n×n bit map
indicating the reconstruction level associated
with each pixel. Decoding is a simple pro-
cess of associating the reconstructed value at
each pixel as per the bit map.
block carry lookahead adder (BCLA)
an adder that uses two levels of carry looka-
head logic.
block-diagram simulator
a simulator
that allows the user to simulate systems as
a combination of block diagrams, each of
which performs a specific function. Each
function is described using a mathematical
equation or a transfer function.
blocked state
See
blocking
.
blocked-rotor current
See
locked-rotor
current
.
blocked-rotor test
an induction motor
test conducted with the shaft held so it cannot
rotate. Typically about 25% of rated voltage
is applied, often at reduced frequency and the
current is measured. The results are used to
determine the winding impedances referred
to the stator.
blocking
state entered if a new user finds
all channels or access mechanisms busy and
hence is denied service. Generally accom-
panied by a busy signal. The call blocking
probability may be given by the Erlang B or
Erlang C formula. See also
adequate service
,
multiple access interference (MAI)
.
blocking artifact
the visibility in an im-
age of rectangular subimages or blocks af-
ter certain types of image processing. Also
called blocking effect distortion.
blocks world
a visual domain, typical
of early studies on machine vision, in which
objects are light, plane-faced solids over a
dark background.
c
2000 by CRC Press LLC