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added dWLm chunk #391

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e93a3e4
added dWLm chunk
digitaltvguy Dec 10, 2023
5977829
Update index.html
svgeesus Aug 13, 2024
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svgeesus Aug 13, 2024
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69 changes: 67 additions & 2 deletions index.html
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Expand Up @@ -291,8 +291,19 @@
publisher: "ITU",
date: "2021-04",
href: "https://www.itu.int/ITU-T/recommendations/rec.aspx?rec=14652"
}
}
},
"ITU-R BT.2408": {
title: "Guidance for operational practices in HDR television production",
publisher: "ITU",
rawDate: "2023-09",
href: "https://www.itu.int/pub/R-REP-BT.2408"
},
"ISO/TS 22028-5": {
title: "Part 5: High dynamic range and wide colour gamut encoding for still images (HDR/WCG)",
publisher: "ISO",
rawDate: "2023-06",
href: "https://www.iso.org/standard/81863.html"
}
}
</script>
</head>
Expand Down Expand Up @@ -4233,6 +4244,60 @@ <h2><span class="chunk">cLLi</span> Content Light Level Information</h2>
</section>
</section>

<section id="dWLm-chunk">
<h2><span class="chunk">dWLm</span> Diffuse white luminance metadata</h2>
<p>The two-byte chunk type field contains the hexadecimal values</p>

<pre>
<!-- xx xx xx xx
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<!-- xx xx xx xx
64 57 4C 6D

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Suggest renaming dWLm chunk to conform with HEIF effort which labels it ndwt (Nominal Diffuse White)

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I support this idea: nDWt.

</pre>
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<p>If present, the <span class="chunk">dWLm</span> chunk stores the luminance value
of the images nominal diffuse white, in cd/m<sup>2</sup> as defined in [ISO/TS 22028-5]:</p>

<p>If the luminance of the diffuse white differs from the nominal luminance for an HDR reference display's
diffuse white as defined in [[ITU-R-BT.2408]], the contents diffuse white luminance level
should be indicated using this metadata.</p>

<p>The following specifies the syntax of the <span class="chunk">dWLn</span> chunk:</p>
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<p>The following specifies the syntax of the <span class="chunk">dWLn</span> chunk:</p>
<p>The following specifies the syntax of the <span class="chunk">dWLm</span> chunk:</p>


<table id="dWLn-chunk-syntax" class="numbered simple">
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<table id="dWLn-chunk-syntax" class="numbered simple">
<table id="dWLm-chunk-syntax" class="numbered simple">

<caption>dWLn chunk components</caption>
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<caption>dWLn chunk components</caption>
<caption>dWLm chunk components</caption>


<tr>
<th>Name</th>
<th>Size</th>
<th>Divisor value</th>
</tr>

<tr>
<td>Diffuse white luminance metadata</td>
<td>4 bytes</td>
<td>1 cd/m<sup>2</sup></td>
</tr>

</table>

<aside class="example">
Example <span class="chunk">dWLn</span> Diffuse white luminance metadata:
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Example <span class="chunk">dWLn</span> Diffuse white luminance metadata:
Example <span class="chunk">dWLm</span> Diffuse white luminance metadata:


<table id="dWLn-diffuse-white-luminance-metadata-example" class="numbered simple">
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<table id="dWLn-diffuse-white-luminance-metadata-example" class="numbered simple">
<table id="dWLm-diffuse-white-luminance-metadata-example" class="numbered simple">

<tr>
<th>Actual value</th>
<th>Stored Decimal value</th>
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<th>Stored Decimal value</th>
<th>Stored decimal value</th>

(although I would prefer to remove this column, as it's redundant because it shows the same information as Actual value)

<th>Stored 2-byte unsigned value</th>
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<th>Stored 2-byte unsigned value</th>

We don't need to say how a uint32_t works, do we? The other chunks don't.

</tr>

<tr>
<td>203 cd/m<sup>2</sup></td>
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203 is a poor example because this metadata is to be used when the diffuse white luminance is not 203!

Suggested change
<td>203 cd/m<sup>2</sup></td>
<td>100 cd/m<sup>2</sup></td>

<td>203</td>
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<td>203</td>
<td>1,000,000</td>

<td>CB 00</td>
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I need to double check the endianness here.
It might be 00 CB?
I'll get back to you on that.

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It should be a PNG unsigned four byte integer anyway, like cLLi

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<td>CB 00</td>

We don't need to say how a uint32_t works, do we?

</tr>
</table>
</aside>
</section>
</section>


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<section id="11textinfo">
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