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Clarifies fallback strategy and editorial clean-up #4

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Jul 7, 2017
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Clarifies fallback strategy and editorial clean-up #4

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f8a35d6
Clarified fallback strategy (issue #1)
palemieux Jun 23, 2017
f31e530
Address https://github.com/w3c/png-hdr-pq/pull/4#discussion_r125535857
palemieux Jul 6, 2017
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55 changes: 33 additions & 22 deletions index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -51,9 +51,9 @@

<body>
<section id="abstract">
<p>This specification defines a mechanism for storing images that use the Reference PQ EOTF specified in [[!BT2100-1]] in the Portable
Network Graphics (PNG) format (specified in [[!PNG]]), without modification to existing chunks or the introduction of new
chunks.</p>
<p>This specification defines a mechanism for storing images that use the Reference PQ EOTF specified in [[!BT2100-1]] in the
Portable Network Graphics (PNG) format (specified in [[!PNG]]), without modification to existing chunks or the introduction of
new chunks.</p>
</section>

<section id="sotd">
Expand All @@ -68,28 +68,38 @@ <h2>Introduction</h2>
commonly used for HDR images.</p>

<p>This specification uses the existing <code>iCCP</code> chunk to unambiguously signal the color system of an image that uses
the Reference PQ EOTF specified in [[!BT2100-1]]</p>
the Reference PQ EOTF specified in [[!BT2100-1]]. It also allows graceful processing by decoders that do not conform to this
specification by recommending fallback values for the <code>gAMA</code> chunk, <code>cHRM</code> chunk, and embedded ICC
profile.</p>
</section>

<section id="file">
<h2>PQ HDR PNG File</h2>

<p>The file shall conform to [[!PNG]].</p>
<p>The file SHALL conform to [[!PNG]].</p>

<p>The image type shall be <code>truecolor</code>.</p>
<p>The image type SHALL be <code>truecolor</code>.</p>

<p>The image shall conform to one of the Pixel Encoding Systems specified in the table below.</p>
<p>The image SHALL conform to one of the Pixel Encoding Systems specified in the table below.</p>

<p>The file shall contain an <code>iCCP</code> chunk whose profile name is set according to the table below.</p>
<p>The file SHALL contain an <code>iCCP</code> chunk, constrained as follows:</p>

<p>The embedded ICC profile of the <code>iCCP</code> chunk, the <code>cHRM</code> chunk and the <code>gAMA</code> chunk should
be set according to the table below.</p>
<ul>
<li>the profile name of the <code>iCCP</code> chunk SHALL be set as specified by the table below according to the Pixel
Encoding System of the image; and</li>

<p>The embedded ICC profile shall be compressed using Method 0, as specified in [[!PNG]].</p>
<li>the embedded ICC profile of the <code>iCCP</code> chunk SHOULD contained one of the ICC profiles specified by the table
below according to the Pixel Encoding System of the image; and</li>

<li>if present, he embedded ICC profile SHALL be compressed using Method 0, as specified in [[!PNG]].</li>
</ul>

<p>The <code>cHRM</code> chunk and the <code>gAMA</code> chunk of the file SHOULD be set as specified by the table below
according to the Pixel Encoding System of the image.</p>

<table id="hdr-systems" style="font-size:small;">
<caption>
HDR Systems
Pixel Encoding Systems
</caption>

<thead>
Expand All @@ -98,7 +108,7 @@ <h2>PQ HDR PNG File</h2>

<th><code>iCCP</code> Chunk Profile Name</th>

<th><code>iCCP</code> Chunk Embedded ICC Profile</th>
<th><code>iCCP</code> Chunk Embedded ICC Profile(s)</th>

<th><code>gAMA</code> Chunk</th>

Expand All @@ -113,7 +123,7 @@ <h2>PQ HDR PNG File</h2>
<td><code>ITUR_2100_PQ_FULL</code></td>

<td>
<a href="icc/ITUR_2100_PQ_FULL.icc">ITUR_2100_PQ_FULL.icc</a>
<a href="icc/ITUR_2100_PQ_FULL.icc">ITUR_2100_PQ_FULL.icc</a>
</td>

<td>15000</td>
Expand Down Expand Up @@ -183,16 +193,17 @@ <h2>PQ HDR PNG File</h2>
</tbody>
</table>

<p class="note">The <code>gAMA</code> and embedded ICC profile are provided solely for compatibility with processors that do
not conform to this specification.</p>
<p class="note">The <code>gAMA</code> chunk and embedded ICC profile specified in the table above are not accurate, and their
processing is not required to reproduce the image as intended by the author. They are provided as fallback for implementations
that do not recognize the semantics associated with a <code>iCCP</code> Chunk Profile Names defined by this specification.
Future versions of this specification might include additional ICC profiles, e.g. to reflect improvements in ICC profile
capabilities.</p>

<p class="note">This specification does not constrain bit depth.</p>
</section>

<section class='appendix' class="informative">
<h2>Privacy and Security Considerations</h2>

See Section 13.4 at [[!PNG]].
</section>

<section class="informative">
<h2>Privacy and Security Considerations</h2>See Section 13.4 at [[!PNG]].
</section>
</body>
</html>