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[Extensions] Add iDOT to "Chunks Not Described Here", #530 #541

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b59b0be
[Extensions] Add iDOT to "Chunks Not Described Here", #530
svgeesus Sep 15, 2025
0833337
Update extensions/Overview.bs
svgeesus Sep 16, 2025
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36 changes: 28 additions & 8 deletions extensions/Overview.bs
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@@ -1,10 +1,10 @@
<pre class='metadata'>
Title: Extensions to the PNG Third Edition Specification, Version 1.6.0
Title: Extensions to the PNG Third Edition Specification, Version 1.6.1
Shortname: pngext
Level: none
Status: NOTE-FPWD
Status: NOTE-WD
Group: PNGWG
URL: https://w3c.github.io/PNG-spec/extensions/Overview.html
URL: https://w3c.github.io/png/extensions/Overview.html
TR: https://w3.org/TR/png-extensions/
Editor: Chris Lilley, W3C, https://svgees.us/, w3cid 1438
Former Editor: Glenn Randers-Pehrson
Expand All @@ -29,15 +29,21 @@ Local Boilerplate: copyright yes
"dSIG-spec": {
"href": "http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.spec.pdf",
"title": "PNG Digital Signatures: Extension Specification",
"authors": "Thomas Kopp",
"authors": ["Thomas Kopp"],
"date": "17 Nov 2008"
},
"dSIG-example": {
"href": "http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.sample.html",
"title": "PNG Digital Signatures: Commented Example",
"authors": "Martin Boßlet, Thomas Kopp",
"authors": ["Martin Boßlet", "Thomas Kopp"],
"date": "18 May 2008"
}
},
"iDOT-description": {
"href": "https://www.hackerfactor.com/blog/index.php?/archives/895-Connecting-the-iDOTs.html",
"title": "Connecting the iDOTs",
"authors": ["Dr. Neal Krawetz"],
"date": "8 September 2020"
}
}
</pre>

Expand Down Expand Up @@ -771,6 +777,20 @@ The <span class="chunk">pCAL</span> chunk contains:
In the future, chunks will be fully specified
before they are registered.

<h3 id="R.iDOT">
<span class="chunk">iDOT</span> Apple Multithreaded Decoding
</h3>

The <span class="chunk">iDOT</span> chunk enables multi-core machines
to use (at least) two cores to decode the PNG datastream.

It was developed by Apple, around 2011, but never registered.
It is commonly found in PNG images generated on Apple hardware.

This chunk has been reverse-engineered, and is described in detail
in a separate document, [[!iDOT-description]].


<h2 id="Keywords">
Text Chunk Keywords
</h2>
Expand Down Expand Up @@ -803,7 +823,7 @@ The <span class="chunk">pCAL</span> chunk contains:
</pre>

This restricted set
is the ISO-646 "invariant" character set [[!ISO 646]].
is the ISO-646 "invariant" character set [[!ISO646]].
These characters have the same numeric codes
in all ISO character sets,
including all national variants of ASCII.
Expand Down Expand Up @@ -1167,7 +1187,7 @@ What are <code>x0</code> and <code>x1</code> for?
not already listed in the PNG specification
are presented in alphabetical order:

</p><ul>
<ul>
<li>Adeluc, <a href="http://www.adeluc.com">www.adeluc.com</a>,
png&nbsp;@&nbsp;adeluc.com
</li><li>Brendan Bolles
Expand Down
54 changes: 30 additions & 24 deletions extensions/Overview.html
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Expand Up @@ -2,12 +2,15 @@
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
<title>Extensions to the PNG Third Edition Specification, Version 1.6.0</title>
<meta content="DNOTE" name="w3c-status">
<title>Extensions to the PNG Third Edition Specification, Version 1.6.1</title>
<meta content="NOTE-WD" name="w3c-status">
<link href="https://www.w3.org/StyleSheets/TR/2021/W3C-DNOTE" rel="stylesheet">
<meta content="Bikeshed version d5d58a306, updated Fri Jan 26 16:12:28 2024 -0800" name="generator">
<meta content="Bikeshed version b25686b9f, updated Fri Mar 14 14:15:20 2025 -0700" name="generator">
<link href="https://w3.org/TR/png-extensions/" rel="canonical">
<meta content="8cfa8a9f1ea4441f47b96cec8bd99b9e011d3bfe" name="revision">
<link href="https://www.w3.org/2008/site/images/favicon.ico" rel="icon">
<meta content="32113571711ea45fc4af71a810cd12bf5a17a60b" name="revision">
<meta content="dark light" name="color-scheme">
<link href="https://www.w3.org/StyleSheets/TR/2021/dark.css" media="(prefers-color-scheme: dark)" rel="stylesheet" type="text/css">
<style>
span.chunk {
font-family: Courier, monospace;
Expand Down Expand Up @@ -537,14 +540,14 @@
<body class="h-entry">
<div class="head">
<p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2021/logos/W3C" width="72"> </a> </p>
<h1 class="p-name no-ref" id="title">Extensions to the PNG Third Edition Specification, Version 1.6.0</h1>
<p id="w3c-state"><a href="https://www.w3.org/standards/types#DNOTE">W3C Group Draft Note</a>, <time class="dt-updated" datetime="2024-02-19">19 February 2024</time></p>
<h1 class="p-name no-ref" id="title">Extensions to the PNG Third Edition Specification, Version 1.6.1</h1>
<p id="w3c-state"><a href="https://www.w3.org/standards/types/#DNOTE">W3C Group Draft Note</a>, <time class="dt-updated" datetime="2025-09-15">15 September 2025</time></p>
<details open>
<summary>More details about this document</summary>
<div data-fill-with="spec-metadata">
<dl>
<dt>This version:
<dd><a class="u-url" href="https://www.w3.org/TR/2024/DNOTE-pngext-20240219/">https://www.w3.org/TR/2024/DNOTE-pngext-20240219/</a>
<dd><a class="u-url" href="https://www.w3.org/TR/2025/DNOTE-pngext-20250915/">https://www.w3.org/TR/2025/DNOTE-pngext-20250915/</a>
<dt>Latest published version:
<dd><a href="https://w3.org/TR/png-extensions/">https://w3.org/TR/png-extensions/</a>
<dt>Editor's Draft:
Expand All @@ -561,7 +564,7 @@ <h1 class="p-name no-ref" id="title">Extensions to the PNG Third Edition Specifi
</div>
</details>
<div data-fill-with="warning"></div>
<p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/policies/#copyright">Copyright</a> © 2024 <a href="https://www.w3.org/">World Wide Web Consortium</a>. <abbr title="World Wide Web Consortium">W3C</abbr><sup>®</sup> <a href="https://www.w3.org/policies/#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/policies/#W3C_Trademarks">trademark</a> and <a href="https://www.w3.org/copyright/software-license/" rel="license" title="W3C Software and Document License">permissive document license</a> rules apply. </p>
<p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/policies/#copyright">Copyright</a> © 2025 <a href="https://www.w3.org/">World Wide Web Consortium</a>. <abbr title="World Wide Web Consortium">W3C</abbr><sup>®</sup> <a href="https://www.w3.org/policies/#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/policies/#W3C_Trademarks">trademark</a> and <a href="https://www.w3.org/copyright/software-license/" rel="license" title="W3C Software and Document License">permissive document license</a> rules apply. </p>
<hr title="Separator for header">
</div>
<div class="p-summary" data-fill-with="abstract">
Expand Down Expand Up @@ -599,15 +602,12 @@ <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
<ol class="toc">
<li><a href="#R.dSIG"><span class="secno">5.1</span> <span class="content"> <span class="chunk">dSIG</span> Digital signature </span></a>
<li><a href="#R.fRAc"><span class="secno">5.2</span> <span class="content"> <span class="chunk">fRAc</span> Fractal image parameters </span></a>
<li><a href="#R.iDOT"><span class="secno">5.3</span> <span class="content"> <span class="chunk">iDOT</span> Apple Multithreaded Decoding </span></a>
</ol>
<li>
<a href="#Keywords"><span class="secno">6</span> <span class="content"> Text Chunk Keywords </span></a>
<ol class="toc">
<li>
<a href="#K.Keywords"><span class="secno">6.1</span> <span class="content"> Additional Registered Keywords </span></a>
<ol class="toc">
<li><a href="#K.Collection"><span class="secno">6.1.1</span> <span class="content"> Collection </span></a>
</ol>
<li><a href="#K.Keywords"><span class="secno">6.1</span> <span class="content"> Additional Registered Keywords </span></a>
<li><a href="#K.Syntax"><span class="secno">6.2</span> <span class="content"> Keyword Syntax </span></a>
</ol>
<li>
Expand Down Expand Up @@ -1322,13 +1322,16 @@ <h3 class="heading settled" data-level="5.2" id="R.fRAc"><span class="secno">5.2
was being developed by Tim Wegner, twegner @ phoenix.net.</p>
<p>In the future, chunks will be fully specified
before they are registered.</p>
<h3 class="heading settled" data-level="5.3" id="R.iDOT"><span class="secno">5.3. </span><span class="content"> <span class="chunk">iDOT</span> Apple Multithreaded Decoding </span><a class="self-link" href="#R.iDOT"></a></h3>
<p>The <span class="chunk">iDOT</span> chunk enables multi-core machines
to use (at least) two cores to decode the PNG datastream.</p>
<p>It was developed by Apple, around 2011, but never registered.
It is commonly found in PNG images generated on Apple hardware.</p>
<p>This chunk has been reverse-engineered, and is described in detail
in a separate document, <a data-link-type="biblio" href="#biblio-idot-description" title="Connecting the iDOTs">[iDOT-description]</a>.</p>
<h2 class="heading settled" data-level="6" id="Keywords"><span class="secno">6. </span><span class="content"> Text Chunk Keywords </span><a class="self-link" href="#Keywords"></a></h2>
<h3 class="heading settled" data-level="6.1" id="K.Keywords"><span class="secno">6.1. </span><span class="content"> Additional Registered Keywords </span><a class="self-link" href="#K.Keywords"></a></h3>
<h4 class="heading settled" data-level="6.1.1" id="K.Collection"><span class="secno">6.1.1. </span><span class="content"> Collection </span><a class="self-link" href="#K.Collection"></a></h4>
<p>Name of a collection
to which the image belongs.
An image may belong to one or more collections,
each named by a separate text chunk.</p>
<p>(none)</p>
<h3 class="heading settled" data-level="6.2" id="K.Syntax"><span class="secno">6.2. </span><span class="content"> Keyword Syntax </span><a class="self-link" href="#K.Syntax"></a></h3>
<p>All registered textual keywords
in text chunks
Expand All @@ -1341,7 +1344,7 @@ <h3 class="heading settled" data-level="6.2" id="K.Syntax"><span class="secno">6
<pre># $ @ [ \ ] ^ ` { | } ~
</pre>
<p>This restricted set
is the ISO-646 "invariant" character set [[!ISO 646]].
is the ISO-646 "invariant" character set <a data-link-type="biblio" href="#biblio-iso646" title="Information technology — ISO 7-bit coded character set for information interchange">[ISO646]</a>.
These characters have the same numeric codes
in all ISO character sets,
including all national variants of ASCII.</p>
Expand Down Expand Up @@ -2278,7 +2281,6 @@ <h3 class="heading settled" data-level="12.2" id="Credits.contrib"><span class="
<p>Names of contributors
not already listed in the PNG specification
are presented in alphabetical order:</p>
<p></p>
<ul>
<li>Adeluc, <a href="http://www.adeluc.com">www.adeluc.com</a>,
png @ adeluc.com
Expand Down Expand Up @@ -2323,21 +2325,25 @@ <h3 class="no-ref no-num heading settled" id="w3c-conventions"><span class="cont
like this: </p>
<p class="note" role="note">Note, this is an informative note.</p>
</div>
<script src="https://www.w3.org/scripts/TR/2021/fixup.js"></script>
<script src="https://www.w3.org/scripts/TR/2021/fixup.js"></script>
<h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
<h3 class="no-num no-ref heading settled" id="normative"><span class="content">Normative References</span><a class="self-link" href="#normative"></a></h3>
<dl>
<dt id="biblio-dsig-spec">[dSIG-spec]
<dd>T; et al. <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.spec.pdf"><cite>PNG Digital Signatures: Extension Specification</cite></a>. 17 Nov 2008. URL: <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.spec.pdf">http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.spec.pdf</a>
<dd>Thomas Kopp. <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.spec.pdf"><cite>PNG Digital Signatures: Extension Specification</cite></a>. 17 Nov 2008. URL: <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.spec.pdf">http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.spec.pdf</a>
<dt id="biblio-idot-description">[iDOT-description]
<dd>Dr. Neal Krawetz. <a href="https://www.hackerfactor.com/blog/index.php?/archives/895-Connecting-the-iDOTs.html"><cite>Connecting the iDOTs</cite></a>. 8 September 2020. URL: <a href="https://www.hackerfactor.com/blog/index.php?/archives/895-Connecting-the-iDOTs.html">https://www.hackerfactor.com/blog/index.php?/archives/895-Connecting-the-iDOTs.html</a>
<dt id="biblio-iso646">[ISO646]
<dd><a href="https://www.iso.org/standard/4777.html"><cite>Information technology — ISO 7-bit coded character set for information interchange</cite></a>. December 1991. Published. URL: <a href="https://www.iso.org/standard/4777.html">https://www.iso.org/standard/4777.html</a>
<dt id="biblio-png">[PNG]
<dd>Chris Lilley; et al. <a href="https://www.w3.org/TR/png-3/"><cite>Portable Network Graphics (PNG) Specification (Third Edition)</cite></a>. 21 September 2023. CR. URL: <a href="https://www.w3.org/TR/png-3/">https://www.w3.org/TR/png-3/</a>
<dd>Chris Lilley; et al. <a href="https://www.w3.org/TR/png-3/"><cite>Portable Network Graphics (PNG) Specification (Third Edition)</cite></a>. 24 June 2025. REC. URL: <a href="https://www.w3.org/TR/png-3/">https://www.w3.org/TR/png-3/</a>
<dt id="biblio-rfc2119">[RFC2119]
<dd>S. Bradner. <a href="https://datatracker.ietf.org/doc/html/rfc2119"><cite>Key words for use in RFCs to Indicate Requirement Levels</cite></a>. March 1997. Best Current Practice. URL: <a href="https://datatracker.ietf.org/doc/html/rfc2119">https://datatracker.ietf.org/doc/html/rfc2119</a>
</dl>
<h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
<dl>
<dt id="biblio-dsig-example">[dSIG-example]
<dd>M; et al. <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.sample.html"><cite>PNG Digital Signatures: Commented Example</cite></a>. 18 May 2008. URL: <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.sample.html">http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.sample.html</a>
<dd>Martin Boßlet; Thomas Kopp. <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.sample.html"><cite>PNG Digital Signatures: Commented Example</cite></a>. 18 May 2008. URL: <a href="http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.sample.html">http://ftp-osl.osuosl.org/pub/libpng/documents/signatures/PNG_Digital_Signatures.sample.html</a>
<dt id="biblio-gif">[GIF]
<dd><a href="https://www.w3.org/Graphics/GIF/spec-gif89a.txt"><cite>Graphics Interchange Format</cite></a>. 31 July 1990. URL: <a href="https://www.w3.org/Graphics/GIF/spec-gif89a.txt">https://www.w3.org/Graphics/GIF/spec-gif89a.txt</a>
</dl>