Page 144 - Electrical Engineering Dictionary

product codes, M/RVQ, I/RVQ, G/SVQ, coding gain (1) the reduction in signal-
CVQ, FSVQ) for codebook design are em- to-noise ratio required for a specified error
ployed to reduce computational costs low. performance in a block or convolutional for-
See also vector quantization, tree structured ward error control system as compared to an
VQ. uncoded system with the same information
rate, channel impairments, and modulation
codebook generation a fundamental and demodulation techniques. In a trellis
problem in vector quantization. Codebooks coded modulation system, it is the ratio of
are typically generated by using a training set the squared free distance in the coded system
of images that are representative of the im- to that of the uncoded system.
ages to be encoded. The best training image (2) the difference between the SNR/bit
to encode a single image is the image itself. (dB) required for an uncoded and a coded
This is called a local codebook. The main system to attain the same arbitrary error prob-
question addressed here is what codevectors ability. Depends on the code parameters and
should be included in the codebook. See also also on the SNR per bit.
vector quantization.
coding of graphics use of a representa-
codebook training the act of designing a tion scheme for graphics. Graphics coding
codebook for a source coding system. The is typically a two-level coding scheme. Both
LBG algorithm is often used to design the exact and approximate methods are applica-
codebook for vector quantizers. ble to this type of coding. Run-length coding,
predictive coding, line-to-line predictive dif-
ferential coding, and block coding are typical
codec word formed from encoder and
for graphic coding.
decoder. A device that performs encoding
and decoding of communications protocols.
coding of line drawings use of a rep-
resentation scheme for line drawings. Line
coded modulation an integrated modu-
drawings are typically coded using chain
lation and coding approach for bandwidth-
codes where the vector joining two succes-
constrained channel where the redundancy
sive pixels are assigned a codeword. Higher
introduced by the code is compensated by
efficiency is obtained by differential chain
increasing the number of signals, for per-
coding in which each pixel is represented by
formance improvement without additional
the difference between two successive abso-
bandwidth or transmission power.
lute codes.
codeword the channel symbol assigned
coding redundancy See redundancy.
by an encoder to a source symbol. Typically
the codeword is a quantized scalar or vector. coefficient of thermal expansion (CTE)
mismatch the difference between the co-
coding the process of programming, gen- efficients of thermal expansion of two com-
erating code in a specific language. The pro- ponents, i.e., the difference in linear thermal
cess of translating data from a representation expansion per unit change in temperature.
form into a different one by using a set of (This term is not to be confused with ther-
rules or tables. See also ASCII, EBCDIC, mal expansion mismatch).
binary.
coefficient of utilization (CU) the ra-
coding at primary rates for videoconfer- tio of the lumens reaching the working plane
encing See image coding for videoconfer- to the total lumens generated by the lamp.
encing. This factor takes into account the efficiency

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2000 by CRC Press LLC