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JPEG XT (ISO/IEC 18477) is an image compression standard which specifies backward-compatible extensions of the base JPEG standard (ISO/IEC 10918-1 and ITU Rec. T.81). JPEG XT extends JPEG with support for higher integer bit depths, high dynamic range imaging and floating-point coding, lossless coding, alpha channel coding, and an extensible file format based on
JFIF The JPEG File Interchange Format (JFIF) is an image file format standard published as ITU-T Recommendation T.871 and ISO/IEC 10918-5. It defines supplementary specifications for the container format that contains the image data encoded with the J ...
. It also includes reference software implementation and conformance testing specification. JPEG XT extensions are backward compatible with base JPEG/JFIF file format - existing software is forward compatible and can read the JPEG XT binary stream, though it would only decode the base 8-bit lossy image.Thomas Richter, Alessandro Artusi, Touradj Ebrahimi, JPEG XT: A new family of JPEG backward-compatible standards, IEEE MultiMedia Magazine, Issue of July/Sept 2016. DOI: 10.1109/MMUL.2016.49. Pre-print version. https://jpeg.org/downloads/jpegxt/IEEE_MM-preprint-AA-TE.pdf


The JPEG XT standard

JPEG standards are formally named as ''Information technology – Scalable compression and coding of continuous-tone still images''. ISO/IEC 18477 consists of the following parts:


Overview

The core Part 1 of the standard defines the JPEG specifications in common use today, such as ISO/IEC 10918-1 (base format), 10918-5 JPEG File Interchange Format (JFIF), and 10918-6 (printing applications). It restricts the JPEG coding modes to baseline, sequential, and progressive Huffman, and includes JFIF definitions of
Rec. 601 ITU-R Recommendation BT.601, more commonly known by the abbreviations Rec. 601 or BT.601 (or its former name CCIR 601) is a standard originally issued in 1982 by the CCIR (an organization, which has since been renamed as the Internatio ...
color space transformations with YCbCr
chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance. It is u ...
.Thomas Richter, Tim Bruylants, Peter Schelkens, Touradj Ebrahimi (22 September 2015)
The JPEG XT Suite of Standards: Status and Future Plans
/ref> The first specification was authored by Thomas Richter from Germany, Tim Bruylants and Peter Schelkens from Belgium, and Swiss-Iranian engineer Touradj Ebrahimi. Part 3 Box file format defines an extensible format which is backward-compatible with JFIF. Extensions are based on 'boxes' - 64 KB chunks tagged by application marker 11 ('APP11'), containing enhancement data layers and additional binary metadata describing how to combine them with the base 8-bit layer to form full-precision image.Alessandro Artusi, Rafal K. Mantiuk, Thomas Richter, Pavel Korshunov, Philippe Hanhart, Touradj Ebrahimi, Massimiliano Agostinelli
JPEG XT: A Compression Standard for HDR and WCG Images (Standards in a Nutshell)
Part 3 builds on the
ISO base media file format The ISO base media file format (ISOBMFF) is a container file format that defines a general structure for files that contain time-based multimedia data such as video and audio. It is standardized in ISO/ IEC 14496-12, a.k.a. MPEG-4 Part 12, and wa ...
used by JPEG 2000; similar arrangement was employed in the earlier
JPEG-HDR JPEG XT (ISO/IEC 18477) is an image compression standard which specifies backward-compatible extensions of the base JPEG standard (ISO/IEC 10918-1 and ITU Rec. T.81). JPEG XT extends JPEG with support for higher integer bit depths, high dynamic ...
format from
Dolby Labs Dolby Laboratories, Inc. (often shortened to Dolby Labs and known simply as Dolby) is an American company specializing in audio noise reduction, audio encoding/compression, spatial audio, and HDR imaging. Dolby licenses its technologies to ...
, which is standardized in JPEG XT Part 2. Part 7 includes floating-point HDR coding tools which produce an enhancement image layer from full-precision image and gamma-corrected tone-mapped 8-bit base image layer. These tools are intended for
high dynamic range imaging In photography and videography, multi-exposure HDR capture is a technique that creates extended or high dynamic range (HDR) images by taking and combining multiple exposures of the same subject matter at different exposure levels. Combining mu ...
with multiple photo exposures and
computer-generated images Computer-generated imagery (CGI) is the use of computer graphics to create or contribute to images in art, printed media, video games, simulators, and visual effects in films, television programs, shorts, commercials, and videos. The images m ...
which exceed linear 16-bit integer precision. It defines three main algorithms for reconstructing the HDR image: Profile A uses a common logarithmic scale factor for inverse tone-mapping of the base layer; Profile B uses a divisor image extension layer scaled by the common exposure value; Profile C is similar to A but uses per-component scaling factors and logarithmic space with piece-wise linear functions, which allows lossless encoding. Profile A is based on the Radiance
RGBE image format RGBE or Radiance HDR is an image format invented by Gregory Ward Larson for the Radiance rendering system. It stores pixels as one byte each for RGB (red, green, and blue) values with a one byte shared exponent. Thus it stores four bytes per pix ...
and Profile B is based on th
XDepth
format fro
Trellis Management
Profile D uses a simple algorithm which does not generate an enhancement image – the enhancement layer is used to store extended precision of discrete cosine transform (DCT) transfer coefficients, and non-gamma transfer function is applied to increase dynamic range to 12 bits. Backward compatibility is limited because legacy decoders do not understand new EOTF curves and produce undersaturated colors. Profile D is not implemented in reference software. JPEG XT also allows mixing of various elements from different profiles in the code stream, allowing extended DCT precision and lossless encoding in all profiles (the 'Full Profile'). Part 6, Integer coding of Intermediate Dynamic Range (IDR) images, is an extension for coding 9 to 16-bit integer samples typical for RAW sensor data; its coding tools are identical to Part 7 Profile C. Part 2 defines a HDR imaging implementation based on JPEG-HDR format from Dolby. It uses RGBE image format defined by Part 7 Profile A, supporting both integer and floating point samples; file format is based on Part 3 but uses proprietary text-based metadata syntax. Part 8 Lossless coding is an extension of integer and floating point coding based on Part 7 Profile C, allowing for scalable lossy to lossless compression. For 10 and 12-bit precision, lossless integer-to-integer DCT is used, which replaces each rotation space with three shearings (similar to wavelet transform in JPEG2000). For 16 bit precision, a lossy fixed-point DCT approximation is specified by the standard and is required for decoders to implement. This makes it possible for the encoder to predict coding errors and store them in the enhancement layer, allowing lossless reconstruction. The error residuals in the enhancement layer can be either uncompressed, or compressed with lossless integer-to-integer DCT. Compression and image quality performance of Part 8 is comparable to PNG. Part 9 Alpha channel extension allows lossy and lossless coding of transparent images and arbitrarily shaped images. It uses an opacity (transparency) layer, encoded with integer or floating point precision, and metadata to specify if content was pre-multiplied with alpha, or pre-multiplied and blended with background color. In the future, privacy protection and security extensions would allow encoding of private image regions (or entire images) with reduced resolution, with digitally encrypted enhancement layers to restore full-resolution image only to those having the private decryption key. Only the public regions will be visible to those not having the key.


JPEG-HDR

JPEG XT Part 2 HDR coding is based on Dolby JPEG-HDR format, created in 2005 by Greg Ward from BrightSide Technologies and Maryann Simmons from
Walt Disney Feature Animation Walt Disney Animation Studios (WDAS), sometimes shortened to Disney Animation, is an American animation studio that creates animated features and short films for The Walt Disney Company. The studio's current production logo features a scene fro ...
as a way to store high dynamic range images inside a standard JPEG file. BrightSide Technologies was acquired by Dolby Laboratories in 2007. The image encoding is based on two-layer
RGBE image format RGBE or Radiance HDR is an image format invented by Gregory Ward Larson for the Radiance rendering system. It stores pixels as one byte each for RGB (red, green, and blue) values with a one byte shared exponent. Thus it stores four bytes per pix ...
used by Radiance renderer, both of which were also created by Ward. Reduction in filesize is achieved by first converting the image into a tone mapped version, then storing a reconstructive multiplier image in APP11 markers in the same JPEG/JFIF file. Ordinary viewing software will ignore the multiplier image allowing anyone to see the tone mapped version of the image presented in a standard dynamic range and color gamut. JPEG-HDR file format is similar to JPEG XT Part 3 Box file format but uses text-based metadata. Programs that support JPEG-HDR include Photosphere by Greg Ward and pfstools.


Reference software

ISO/IEC
Joint Photography Experts Group The Joint Photographic Experts Group (JPEG) is the joint committee between ISO/ IEC JTC 1/ SC 29 and ITU-T Study Group 16 that created and maintains the JPEG, JPEG 2000, JPEG XR, JPEG XT, JPEG XS, JPEG XL, and related digital image standards. It a ...
maintains a reference software implementation for base JPEG (ISO/IEC 10918-1 and 18477-1) and JPEG XT extensions (ISO/IEC 18477 Parts 2 and 6-9), as well as
JPEG-LS Lossless JPEG is a 1993 addition to JPEG standard by the Joint Photographic Experts Group to enable lossless compression. However, the term may also be used to refer to all lossless compression schemes developed by the group, including JPEG 2000 a ...
(ISO/IEC 14495). A reduced version without JPEG-LS, arithmetic coding, and a mozjpeg-like hierarchical progressive coder is available under the ISO license. As a contestant for the ICIP Grand Challenge, the author also includes some existing JPEG optimization techniques known as "JPEG on steroids" in the library. A software JPEG-HDR encoder is provided by Dolby Labs; JPEG XT Part 7 Profile B software is provided by XDepth/Trellis Management; an implementation of all remaining parts was provided by the University of Stuttgart.


Patent pool

In April 2019, Luxembourg-based Sisvel announced the formation of a patent pool for JPEG-XT, although there is no list of claimed patents as of July 2021. Members of the pools included Dolby International AB and Trellis Europe S.r.l. Sisvel's standard prices are .12 Euros for camera-based devices, and .06 Euros for camera-enabled devices.


See also

* JPEG *
JPEG-LS Lossless JPEG is a 1993 addition to JPEG standard by the Joint Photographic Experts Group to enable lossless compression. However, the term may also be used to refer to all lossless compression schemes developed by the group, including JPEG 2000 a ...
* JPEG 2000 *
JPEG XR JPEG XR (JPEG extended range) is an image compression standard for continuous tone photographic images, based on the HD Photo (formerly Windows Media Photo) specifications that Microsoft originally developed and patented. It supports both lossy a ...
*
JPEG-HDR JPEG XT (ISO/IEC 18477) is an image compression standard which specifies backward-compatible extensions of the base JPEG standard (ISO/IEC 10918-1 and ITU Rec. T.81). JPEG XT extends JPEG with support for higher integer bit depths, high dynamic ...
* JPEG XL


References


Publications


JPEG-HDR: A Backwards-Compatible, High Dynamic Range Extension to JPEG
(pdf) *


External links


Official Joint Photographic Experts Group (JPEG) site

jpeg.org/jpegxt/Art of HDRBrightSide Technologies JPEG-HDR encoder
(archived version)
KODAK PROFESSIONAL Extended Range Imaging Technology
{{DEFAULTSORT:JPEG XT XT Graphics file formats IEC standards ISO standards High dynamic range file formats Lossy compression algorithms Lossless compression algorithms Open formats Image compression Computer-related introductions in 2015 Belgian inventions German inventions Iranian inventions Swiss inventions