ISO/IEC 18477-9:2016 情報技術—連続トーン静止画像のスケーラブルな圧縮とコーディング—パート9：アルファチャネルコーディング | ページ 6

3.1.1

ASCII encoding

encoding of text characters and text strings according to ISO/IEC 10646

3.1.2

base decoding path

process of decoding legacy codestream and refinement data to the base image, jointly with all further steps until residual data is added to the values obtained from the residual codestream

3.1.3

base image

collection of sample values obtained by entropy decoding the DCT coefficients of the legacy codestream and the refinement codestream, and inversely DCT transforming them jointly

3.1.4

alpha channel

additional scalar image channel that encodes the opacity of each sample in the main image

3.1.5

alpha component

synonym for alpha channel

3.1.6

binary decision

choice between two alternatives

3.1.7

block

8×8 array of samples or an 8×8 array of DCT coefficient values of one component

3.1.8

box

structured collection of data describing the image or the image decoding process embedded into one or multiple APP₁₁ marker segments

Note 1 to entry: See ISO/IEC 18477-3:2015, Annex B for the definition of boxes.

3.1.9

byte

group of 8 bits

3.1.10

coder

embodiment of a coding process

3.1.11

coding

encoding or decoding

3.1.12

coding process

general reference to an encoding process, a decoding process, or both

3.1.13

compression

reduction in the number of bits used to represent source image data

3.1.14

component

two-dimensional array of samples having the same designation in the output or display device

Note 1 to entry: An image typically consists of several components, e.g. red, green and blue.

3.1.15

composition

process of merging the decoded image data with background image data using opacity information and generating one single final output image

3.1.16

continuous-tone image

image whose components have more than one bit per sample

3.1.17

decoder

embodiment of a decoding process

3.1.18

decoding process

process which takes as its input compressed image data and outputs a continuous-tone image

3.1.19

encoder

embodiment of an encoding process

3.1.20

encoding process

process which takes as its input a continuous-tone image and outputs compressed image data

3.1.21

entropy decoder

embodiment of an entropy decoding procedure

3.1.22

entropy decoding

lossless procedure which recovers the sequence of symbols from the sequence of bits produced by the entropy encoder

3.1.23

entropy encoder

embodiment of an entropy encoding procedure

3.1.24

entropy encoding

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

3.1.25

fixed point discrete cosine transformation

fixed point DCT

implementation of the discrete cosine transformation based on fixed point arithmetic following the specifications in ISO/IEC 18477-8:2016, Annex E

3.1.26

high dynamic range

HDR

image or image data comprised of more than eight bits per sample

3.1.27

integer based discrete cosine transformation

integer point DCT

transformation of an 8×8 sample block from the spatial domain to the frequency domain using the integer approximation of the discrete cosine transformation as specified in ISO/IEC 18477-8:2016, Annex E

3.1.28

joint photographic experts group

JPEG

informal name of the committee which created this document

Note 1 to entry: The"joint" comes from the ITU-T and ISO/IEC collaboration.

3.1.29

legacy codestream

collection of markers and syntax elements defined by Rec. ITU-T T.81 | ISO/IEC 10918-1 bare any syntax elements defined by the ISO/IEC 18477 family of standards. That is, the legacy codestream consists of the collection of all markers except those APP₁₁ markers that describe JPEG XT boxes by the syntax defined in ISO/IEC 18477-3:2015, Annex A

3.1.30

legacy decoding path

collection of operations to be performed on the entropy coded data as described by Rec. ITU-T T.81 | ISO/IEC 10918-1 jointly with the Legacy Refinement scans before this data is merged with the residual data to form the final output image

3.1.31

legacy decoder

embodiment of a decoding process conforming to Rec. ITU-T T.81 | ISO/IEC 10918-1, confined to the lossy DCT process and the baseline, sequential or progressive modes, decoding at most four components to eight bits per component

3.1.32

lossless

encoding and decoding processes and procedures in which the output of the decoding procedure(s) is identical to the input to the encoding procedure(s)

3.1.33

lossless coding

mode of operation which refers to any one of the coding processes defined in ISO/IEC 18477-8:2016 in which all of the procedures are lossless

3.1.34

lossy

encoding and decoding processes which are not lossless

3.1.35

low-dynamic range

LDR

image or image data comprised of data with no more than eight bits per sample

3.1.36

pixel

collection of sample values in the spatial image domain having all the same sample coordinates, e.g. a pixel may consist of three samples describing its red, green and blue value

3.1.37

point transformation

application of a location independent global function to reconstructed sample values in the spatial domain

3.1.38

precision

number of bits allocated to a particular sample or DCT coefficient

3.1.39

premultiplied content

image component that has already multiplied by the scaled value of the alpha channel on a pixel-by-pixel basis to ease the composition of the image with the background

3.1.40

procedure

set of steps which accomplishes one of the tasks which comprise an encoding or decoding process

3.1.41

quantize

act of performing the quantization procedure for a DCT coefficient

3.1.42

residual decoding path

collection of operations applied to the entropy coded data contained in the residual data box and residual refinement scan boxes up to the point where this data is merged with the base image to form the final output image

3.1.43

residual image

sample values as reconstructed by inverse quantization and inverse DCT transformation applied to the entropy-decoded coefficients described by the residual scan and residual refinement scans

3.1.44

residual scan

additional pass over the image data invisible to legacy decoders which provides additive and/or multiplicative correction data of the legacy scans to allow reproduction of high-dynamic range or wide colour gamut data

3.1.45

refinement scan

additional pass over the image data invisible to legacy decoders which provides additional least significant bits to extend the precision of the DCT transformed coefficients

Note 1 to entry: Refinement scans can be either applied in the legacy or residual decoding path.

3.1.46

sample

one element in the two-dimensional image array which comprises a component

3.1.47

sample grid

common coordinate system for all samples of an image

Note 1 to entry: The samples at the top left edge of the image have the coordinates (0,0), the first coordinate increases towards the right, the second towards the bottom.

3.1.48

superbox

box that carries other boxes as payload data

3.1.49

sub box

box that is contained as payload data within a superbox