background image
ISO/IEC 10918-1 : 1993(E)
3.1.35
DC coefficient:
The DCT coefficient for which the frequency is zero in both dimensions.
3.1.36
DC prediction:
The procedure used by DCT-based encoders whereby the quantized DC coefficient from the
previously encoded 8
8 block of the same component is subtracted from the current quantized DC coefficient.
3.1.37
(DCT) coefficient:
The amplitude of a specific cosine basis function may refer to an original DCT coefficient,
to a quantized DCT coefficient, or to a dequantized DCT coefficient.
3.1.38
decoder:
An embodiment of a decoding process.
3.1.39
decoding process:
A process which takes as its input compressed image data and outputs a continuous-tone
image.
3.1.40
default conditioning:
The values defined for the arithmetic coding conditioning tables at the beginning of
coding of an image.
3.1.41
dequantization:
The inverse procedure to quantization by which the decoder recovers a representation of the
DCT coefficients.
3.1.42
differential component:
The difference between an input component derived from the source image and the
corresponding reference component derived from the preceding frame for that component (in hierarchical mode coding).
3.1.43
differential frame:
A frame in a hierarchical process in which differential components are either encoded or
decoded.
3.1.44
(digital) reconstructed image (data):
A continuous-tone image which is the output of any decoder defined in
this Specification.
3.1.45
(digital) source image (data):
A continuous-tone image used as input to any encoder defined in this
Specification.
3.1.46
(digital) (still) image:
A set of two-dimensional arrays of integer data.
3.1.47
discrete cosine transform; DCT:
Either the forward discrete cosine transform or the inverse discrete cosine
transform.
3.1.48
downsampling (filter):
A procedure by which the spatial resolution of an image is reduced (in hierarchical
mode coding).
3.1.49
encoder:
An embodiment of an encoding process.
3.1.50
encoding process:
A process which takes as its input a continuous-tone image and outputs compressed image
data.
3.1.51
entropy-coded (data) segment:
An independently decodable sequence of entropy encoded bytes of compressed
image data.
3.1.52
(entropy-coded segment) pointer:
The variable which points to the most recently placed (or fetched) byte in
the entropy encoded segment.
3.1.53
entropy decoder:
An embodiment of an entropy decoding procedure.
3.1.54
entropy decoding:
A lossless procedure which recovers the sequence of symbols from the sequence of bits
produced by the entropy encoder.
3.1.55
entropy encoder:
An embodiment of an entropy encoding procedure.
3.1.56
entropy encoding:
A lossless procedure which converts a sequence of input symbols into a sequence of bits
such that the average number of bits per symbol approaches the entropy of the input symbols.
3.1.57
extended (DCT-based) process:
A descriptive term for DCT-based encoding and decoding processes in which
additional capabilities are added to the baseline sequential process.
3.1.58
forward discrete cosine transform; FDCT:
A mathematical transformation using cosine basis functions which
converts a block of samples into a corresponding block of original DCT coefficients.
CCITT Rec. T.81 (1992 E)
3
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