ISO/IEC 18477-8:2016

Information technology — Scalable compression and coding of continuous-tone still images — Part 8: Lossless and near-lossless coding

ISO/IEC 18477-8:2016 specifies a coding format, referred to as JPEG XT, which is designed primarily for continuous-tone photographic content.

Technologies de l'information — Compression échelonnable et codage d'images plates en ton continu — Partie 8: Titre manque

General Information

• Status: Withdrawn
• Publication Date: 13-Oct-2016
• Withdrawal Date: 13-Oct-2016
• ICS: 35.040 - Information coding
• ICS: 35.040.30 - Coding of graphical and photographical information
• Technical Committee: ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
• Drafting Committee: ISO/IEC JTC 1/SC 29/WG 1 - JPEG Coding of digital representations of images
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 29-May-2020

Relations

• Revised: ISO/IEC 18477-8:2020 - Information technology — Scalable compression and coding of continuous-tone still images — Part 8: Lossless and near-lossless coding
• Effective Date: 23-Apr-2020

Standards Content (Sample)

INTERNATIONAL ISO/IEC
STANDARD 18477-8
First edition
2016-10-15
Information technology — Scalable
compression and coding of
continuous-tone still images —
Part 8:
Lossless and near-lossless coding
Technologies de l’information — Compression échelonnable et codage
d’images plates en ton continu
Reference number
ISO/IEC 18477-8:2016(E)
©
ISO/IEC 2016

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ISO/IEC 18477-8:2016(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
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ISO/IEC 18477-8:2016(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Symbols . 7
3.3 Abbreviated terms . 7
4 Conventions . 7
4.1 Conformance language . 7
4.2 Operators . 8
4.2.1 Arithmetic operators . 8
4.2.2 Logical operators . 8
4.2.3 Relational operators . 8
4.2.4 Precedence order of operators . 8
4.2.5 Mathematical functions . 9
5 General . 9
5.1 General definitions . 9
5.2 Overview of ISO/IEC 18477-8 . 9
5.3 Profiles .11
5.4 Encoder requirements .11
5.5 Decoder requirements.12
Annex A (normative) Encoding and decoding process .13
Annex B (normative) Boxes .18
Annex C (normative) Multi-component decorrelation transformation .26
Annex D (normative) Entropy coding of residual data in the DCT-bypass and large range mode .30
Annex E (normative) Discrete cosine transformation .41
Annex F (normative) Component upsampling .54
Annex G (normative) Quantization and noise shaping for the DCT-bypass process .56
Annex H (normative) Profiles .59
Bibliography .60
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ISO/IEC 18477-8:2016(E)

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical
activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work. In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for
the different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/IEC JTC 1, Information technology, SC29, Coding of
audio, picture, multimedia and hypermedia information.
A list of all parts in the ISO 18477 series, published under the general title Information technology —
Scalable compression and coding of continuous-tone still images, can be found on the ISO website.
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ISO/IEC 18477-8:2016(E)

Introduction
This document specifies a coded codestream format for storage of continuous-tone high and low
dynamic range photographic content. JPEG XT part 8 is a scalable lossy to lossless image coding system
supporting multiple component images consisting of integer samples between 8- and 16-bit resolution,
or floating point samples of 16-bit resolution. It is by itself an extension of ISO/IEC 18477-6 and
ISO/IEC 18477-7, which specify intermediate range and high-dynamic range image decoding algorithms.
Both of these are based on the box-based file format specified in ISO/IEC 18477-3, which is again an
extension of ISO/IEC 18477-1; the codestream is composed in such a way that legacy applications
conforming to Rec. ITU-T T.81 | ISO/IEC 10918-1 are able to reconstruct a lossy, low dynamic range,
8 bits per sample version of the image.
Today, the most widely used digital photography format, a minimal implementation of JPEG (specified
in Rec. ITU-T T.81 | ISO/IEC 10918-1), uses a bit depth of 8; each of the three channels that together
compose an image pixel is represented by 8 bits, providing 256 representable values per channel.
For more demanding applications, it is not uncommon to use a bit depth of 16, providing 65 536
14
representable values to describe each channel within a pixel, resulting in over 2.8 x 10 representable
colour values. In some less common scenarios, even greater bit depths are used, requiring a floating-
point sample representation.
Most common photo and image formats use an 8-bit or 16-bit unsigned integer value to represent some
function of the intensity of each colour channel. While it might be theoretically possible to agree on
one method for assigning specific numerical values to real world colours, doing so is not practical.
Since any specific device has its own limited range for colour reproduction, the device’s range may be a
small portion of the agreed-upon universal colour range. As a result, such an approach is an extremely
inefficient use of the available numerical values, especially when using only 8 bits (or 256 unique
values) per channel. To represent pixel values as efficiently as possible, devices use a numeric encoding
optimized for their own range of possible colours or gamut.
This part of JPEG XT is primarily designed to encode intermediate or high dynamic image sample values
without loss, or with a precisely controllable bounded loss using the tools defined in ISO/IEC 18477-
1 and some minimal extensions of those tools. The goal is to provide a backwards compatible coding
specification that allows legacy applications and existing toolchains to continue to operate on
codestreams conforming to this document.
JPEG XT has been designed to be backwards compatible to legacy applications while at the same time
having a small coding complexity; JPEG XT uses, whenever possible, functional blocks of Rec. ITU-T T.81
| ISO/IEC 10918-1 to extend the functionality of the legacy JPEG Coding System. It is optimized for
storage and transmission of intermediate and high dynamic range and wide colour gamut 8- to 16-
bit integer or 16-bit floating point images while also enabling low-complexity encoder and decoder
implementations.
This document is an extension of ISO/IEC 18477-1, a compression system for continuous tone digital
still images which is backwards compatible with Rec. ITU-T T.81 | ISO/IEC 10918-1. That is, legacy
applications conforming to Rec. ITU-T T.81 | ISO/IEC 10918-1 will be able to reconstruct streams
generated by an encoder conforming to this document, though will possibly not be able to reconstruct
such streams in full dynamic range, full quality or without loss.
This document is itself based on ISO/IEC 18477-3 that defines a box-based file format similar to
other JPEG standards. It also contains elements of ISO/IEC 18477-6 and ISO/IEC 18477-7. The aim
of this document is to provide a migration path for legacy applications to support lossless coding of
intermediate and high dynamic range images, that is images that are either represented by sample
values requiring 8- to 16-bit precision, or even using 16-bit floating point sample resolution. While Rec.
ITU-T T.81 | ISO/IEC 10918-1 already defines a lossless mode for integer samples, images encoded in
this mode cannot be decoded by applications only supporting the lossy 8-bit-mode; the coding engine
for lossless coding in Rec. ITU-T T.81 | ISO/IEC 10918-1 is completely different from the lossy coding
mode. Unlike the legacy standard, this document defines a lossless scalable coding engine supporting
all bit depths between 8 and 16 bits per sample, including 16-bit floating point samples, while also
staying compatible with legacy applications. Such applications will continue to work, but will only able
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to reconstruct a lossy 8-bit standard low dynamic range (LDR) version of the full image contained in
the codestream. The parts of ISO/IEC 18477 specify a coded file format, referred to as JPEG XT, which is
designed primarily for storage and interchange of continuous-tone photographic content.
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INTERNATIONAL STANDARD ISO/IEC 18477-8:2016(E)
Information technology — Scalable compression and
coding of continuous-tone still images —
Part 8:
Lossless and near-lossless coding
1 Scope
This document specifies a coding format, referred to as JPEG XT, which is designed primarily for
continuous-tone photographic content.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 18477-1:2015, Information technology — Scalable compression and coding of continuous-tone still
images — Part 1: Scalable compression and coding of continuous-tone still images
ISO/IEC 18477-3:2015, Information technology — Scalable compression and coding of continuous-tone still
images — Part 3: Box file format
ISO/IEC 18477-6:2016, Information technology — Scalable compression and coding of continuous-tone
still images — Part 6: IDR Integer Coding
ISO/IEC 18477-7:2016, Information technology — Scalable compression and coding of continuous-tone still
images — Part 7: HDR Floating-Point Coding
ITU-T T.81 | ISO/IEC 10918-1,Information technology — Digital compression and coding of continuous
tone still images — Requirements and guidelines
ITU-T BT.601,Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9
aspect ratios
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
AC coefficient
any DCT coefficient for which the frequency is not zero in at least one dimension
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3.1.2
ASCII encoding
encoding of text characters and text strings according to ISO/IEC 10646
3.1.3
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
3.1.4
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
3.1.5
block
8×8 array of samples or an 8×8 array of DCT coefficient values of one component
3.1.6
box
structured collection of data describing the image or the image decoding process embedded into one or
multiple APP marker segments
11
Note 1 to entry: See ISO/IEC 18477-3:2015, Annex B for the definition of boxes.
3.1.7
byte
group of 8 bits
3.1.8
coding
encoding or decoding
3.1.9
coding process
general reference to an encoding process, a decoding process, or both
3.1.10
compression
reduction in the number of bits used to represent source image data
3.1.11
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.
3.1.12
continuous-tone image
image whose components have more than one bit per sample
3.1.13
DC coefficient
DCT coefficient for which the frequency is zero in both dimensions
3.1.14
DCT coefficient
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
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3.1.15
decoder
embodiment of a decoding process
3.1.16
decoding process
process which takes as its input compressed image data and outputs a continuous-tone image
3.1.17
dequantization
inverse procedure to quantization by which the decoder recovers a representation of the DCT
coefficients
3.1.18
discrete cosine transform
DCT
either the forward discrete cosine transform or the inverse discrete cosine transform
3.1.19
downsampling
procedure by which the spatial resolution of a component is reduced
3.1.20
encoder
embodiment of an encoding process
3.1.21
encoding process
process which takes as its input a continuous-tone image and outputs compressed image data
3.1.22
entropy decoder
embodiment of an entropy decoding procedure
3.1.23
entropy decoding
lossless procedure which recovers the sequence of symbols from the sequence of bits produced by the
entropy encoder
3.1.24
entropy encoder
embodiment of an entropy encoding procedure
3.1.25
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
3.1.26
extension image
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
[SOURCE: ISO/IEC 18477-6:2016, 3.1.54]
3.1.27
fixed point discrete cosine transformation
implementation of the discrete cosine transformation based on fixed point arithmetic following the
specifications in Annex E
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3.1.28
forward DCT bypass
transformation that takes an 8×8 sample block and prepares it for entropy coding without applying a
discrete cosine transformation
3.1.29
forward fixed point DCT
transformation of an 8×8 sample block from the spatial domain to the frequency domain using the fixed
point arithmetic as specified in Annex E
3.1.30
forward integer 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 Annex E
3.1.31
inverse DCT bypass
transformation that takes an 8×8 sample block as generated by entropy decoding and level-shifts it
without applying a discrete cosine transformation
3.1.32
inverse fixed point DCT
transformation of an 8×8 sample block from the frequency domain to the spatial domain using the fixed
point arithmetic as specified in Annex E
3.1.33
inverse integer DCT
the transformation of an 8×8 sample block from the frequency domain to the spatial domain using the
integer approximation of the discrete cosine transformation as specified in Annex E
3.1.34
frequency
two-dimensional index into the two-dimensional array of DCT coefficients
[SOURCE: ISO/IEC 10918-1:1994, 3.1.61]
3.1.35
high dynamic range
HDR
image or image data comprised of more than eight bits per sample
3.1.36
Huffman encoding
entropy encoding procedure which assigns a variable length code to each input symbol
3.1.37
intermediate dynamic range
image or image data comprised of more than eight bits per sample
3.1.38
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.
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3.1.39
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 family ISO/IEC 18477 standards, i.e., the legacy codestream consists of the
collection of all markers except those APP markers that describe JPEG XT boxes by the syntax defined
11
in ISO/IEC 18477-3:2015, Annex A
3.1.40
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
3.1.41
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)
3.1.42
lossless coding
mode of operation which refers to any one of the coding processes defined in ISO/IEC 18477-8 in which
all of the procedures are lossless
3.1.43
lossy
encoding and decoding processes which are not lossless
3.1.44
low-dynamic range
LDR
image or image data comprised of data with no more than eight bits per sample
3.1.45
marker
two-byte code in which the first byte is hexadecimal FF and the second byte is a value between 1 and
hexadecimal FE
3.1.46
marker segment
marker together with its associated set of parameters
3.1.47
noise shaping
signal processing technique that removes quantization noise from the low frequency components and
injects it into the high frequency domain where it can be removed by filtering
3.1.48
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
3.1.49
point transformation
application of a location independent global function to reconstructed sample values in the spatial domain
3.1.50
precision
number of bits allocated to a particular sample or DCT coefficient
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3.1.51
procedure
set of steps which accomplishes one of the tasks which comprise an encoding or decoding process
3.1.52
quantization value
integer value used in the quantization procedure
3.1.53
quantize
act of performing the quantization procedure for a DCT coefficient
3.1.54
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 legacy data to form
the final output image
3.1.55
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
3.1.56
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
3.1.57
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.
3.1.58
sample
one element in the two-dimensional image array which comprises a component
3.1.59
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.
3.1.60
superbox
box that carries other boxes as payload data
3.1.61
sub box
box that is contained as payload data within a superbox
3.1.62
uniform quantization
procedure by which DCT coefficients are linearly scaled in order to achieve compression
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3.1.63
upsampling
procedure by which the spatial resolution of a component is increased
3.2 Symbols
X width of the sample grid in positions
Y height of the sample grid in positions
Nf number of components in an image
s subsampling factor of component i in horizontal direction
i,x
s subsampling factor of component i in vertical direction
i,y
H subsampling indicator of component i in the frame header
i
V subsampling indicator of component i in the frame header
i
v sample value at the sample grid position x,y
x,y
R additional number of DCT coefficients bits represented by refinement scans in the base image,
h
8+R is the number of non-fractional bits (i.e. bits in front of the “binary dot”) of the output of
h
the inverse DCT process in the base image
R additional number of DCT coefficients bits represented by refinement scans in the residual, P+R
r h
is the number of non-fractional bits (i.e. bits in front of the “binary dot”) of the output of the
inverse DCT process in the residual image where P is the bitdepth indicated in the frame header
of the residual codestream
R additional bits in the HDR image. 8+Rb is the sample precision of the reconstructed HDR image
b
3.3 Abbreviated terms
ASCII American Standard Code for Information Interchange
LSB least significant bit
MSB most significant bit
TMO tone mapping operator
DCT discrete cosine transformation
FCT fixed point multi-component transformation
ICT irreversible multi-component transformation
RCT reversible multi component transformation
4 Conventions
4.1 Conformance language
The keyword “reserved” indicates a provision that is not specified at this time, shall not be used, and
may be specified in the future. The keyword “forbidden” indicates “reserved” and in addition indicates
that the provision will never be specified in the future.
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4.2 Operators
NOTE Many of the operators used in this document are similar to those used in the C programming language.
4.2.1 Arithmetic operators
+ addition
− subtraction (as a binary operator) or negation (as a unary prefix operator)
* multiplication
/ division without truncation or rounding
smod
 
 
x smod a is the unique value y between −−a 12/ and a −12/
() ()
   
 
 
for which y+N*a = x with a suitable integer N
umod x umod a is the unique value y bet ween 0 and a−1 for which
y+N*a = x with a suitable integer N
4.2.2 Logical operators
|| logical OR
&& logical AND
! logical NOT
∈ x ∈ {A, B} is defined as (x == A || x == B)
∉ x ∉ {A, B} is defined as (x != A && x != B)
4.2.3 Relational operators
> greater than
>= greater than or equal to
< less than
<= less than or equal to
== equal to
!= not equal to
4.2.4 Precedence order of operators
Operators are listed below in descending order of precedence. If several operators appear in the same
line, they have equal precedence. When several operators of equal precedence appear at the same level
in an expression, evaluation proceeds according to the associativity of the operator either from right to
left or from left to right.
Operators Type of operation Associativity
(), [ ], . expression left to right
− unary negation
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*, / multiplication left to right
umod, smod modulo (remainder) left to r
...