**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**