Page 168 - Electrical Engineering Dictionary

must consist of one or several closed curves, from a uniform field of the same mean lu-
one for the outer contour, and the others (if minance, and the contrast sensitivity is the
any) for the inner contours surrounding any inverse of the threshold contrast. See also
holes. See contour filling, contour following, human visual system.
edge.
control intervention, by means of appro-
contour filling an object contour is gen- priate manipulated inputs, into the controlled
erally built with an edge detector, but such process in the course of its operation; some
a contour can be open, because some of its form of observation of the actual controlled
pieces, not recognized by the edge detector, process behavior is usually being used by the
may be missing. To close the contour, miss- controller.
ing pieces can be added by an operator filling
small holes in a contour. See contour, edge control and status register (CSR) an
detection. internal CPU register that contains a packed
bit array of I/O control information. CSRs
contour following an operator which, can reside on I/O devices as well.
starting from a contour point, follows the
closed curve made by that contour. See control bus contains processor signals
contour. used to interface with all external circuitry,
such as memory and I/O read/write signals,
contrast (1) a measure of the intensity interrupt, and bus arbitration signals.
difference (ratio) between an object and the
image background. control channel the control channel
(2) the difference in the perception of vi- usedtotransmitnetworkcontrolinformation.
sual energy between picture white and pic- No user information is sent on this channel.
ture black. The ratio between the darkest and Compare with traffic channel.
lightest portions of a TV picture.
control chart plot of data over time in-
contrast enhancement alteration of dicating the fluctuation of the main statisti-
the contrast in an image to yield more cal characteristics applied in statistical qual-
details or more information. See also ity control. Control charts can be used to
contrast, histogram stretching, histogram determine if a process is in a state of statis-
equalization. tical control by examining past data and to
determine control limits that would apply to
contrast enhancement layer (CEL) a future data in order to check if the process
highly bleachable coating on top of the pho- maintains in this state.
toresist that serves to enhance the contrast of The individual observations are plotted
an aerial image projected through it. against three lines. The center one represents
an estimate of the process mean, standard
contrast rendition factor (CRF) the ra- deviation or other statistic, two others rep-
tio of visual task contrast with a given light- resent the lower control limit (LCL) and the
ing environment to the contrast with sphere upper control limit (UCL), respectively. If
illumination. the control charts are being used for the first
time, it is necessary to determine trial con-
contrast sensitivity the responsiveness of trol limits.These limits should be revised if
the human visual system to low contrast pat- the points outside them are traced to a special
terns. In psychophysics, the threshold con- cause which can be removed. The most fre-
trast is the minimum contrast needed to dis- quently used control charts are X, s (mean,
¯
¯
tinguish a pattern (such as a spatial sinusoid) standard deviation) and X, R (mean, range)

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