added dWLm chunk #391

digitaltvguy · 2023-12-10T14:17:52Z

Add dWLm chunk
Added ITI BT.2408 reference
Added ISO 22028-5 reference

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ProgramMax · 2023-12-10T22:06:56Z

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+             <tr>
+               <td>203 cd/m<sup>2</sup></td>
+               <td>203</td>
+               <td>CB 00</td>


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

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

index.html

leo-barnes · 2023-12-11T08:35:57Z

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+
+           <tr>
+             <td>Diffuse white luminance metadata</td>
+             <td>2 bytes</td>


Here's the HEIF TuC document that contains proposed language for this same piece of metadata (look for ndwt):
https://www.mpeg.org/wp-content/uploads/mpeg_meetings/144_Hannover/w23211.zip

I think it would be beneficial to make this a uint32_t with a unit of 0.0001 cd/m^2 so that we could have lossless metadata conversion between PNG and HEIF.

I have pinged folks internally on whether diffuse_white_light_x/y would be good additions as well.

I agree, and 4 bytes unsigned integer with that divisor would be consistent with cLLi as well

@podborski mentioned the following regarding the x/y values:

IIRC it was bound to the reference viewing environment and was specified in 22028-5 and we needed a way to carry that metadata in HEIF.

I'm not sure I follow. And I don't have access to ISO 22028-5 to check for myself.
Does 22028-5 specify 4 bytes here? Thus, this comment would put us in line with both 22028-5 and HEIF?
Or does 22028-5 specify 2 bytes and HEIF is different from 22028-5?

I'm not sure I follow. And I don't have access to ISO 22028-5 to check for myself. Does 22028-5 specify 4 bytes here? Thus, this comment would put us in line with both 22028-5 and HEIF? Or does 22028-5 specify 2 bytes and HEIF is different from 22028-5?

From ISO/DTS 22028-5:

4.5.5 Default nominal diffuse white luminance

The default nominal diffuse white luminance shall be 203 cd/m2.

NOTE This nominal luminance value is defined in ITU-R BT.2408-4 as the HDR Reference White.

If the reference nominal diffuse white for specific content has a different displayed luminance, the
reference nominal diffuse white for that content should be indicated using metadata, as defined in 4.6.5.

and then

4.6.5 Diffuse white luminance metadata

The diffuse white luminance metadata stores the luminance value of the reference nominal diffuse
white, in cd/m2.

If the luminance of the diffuse white differs from the default reference display nominal diffuse white
luminance defined in 4.5.5, it should be indicated using metadata.

So the encoding is not defined at all. Also, it is clear that this metadata is only to be used when media white has a luminance other than 203 cd/m²

The diffuse_white_light_x/y fields have been removed from the HEIF text. Latest text can be found here:
https://dms.mpeg.expert/doc_end_user/documents/147_Sapporo/wg11/MDS24143_WG03_N01297.zip

That looks like a good change to me. Merely noting a different white point without also specifying a chromatic adaptation transform (CAT) is not especially helpful, and the most useful information (for PQ, at least) is the absolute luminance of the media white.

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svgeesus · 2023-12-11T14:11:30Z

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+        <p>The two-byte chunk type field contains the hexadecimal values</p>
+
+        <pre>
+<!-- xx xx xx xx


Suggested change

<!-- xx xx xx xx

64 57 4C 6D

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

I support this idea: nDWt.

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svgeesus

Field should be uint32_t

ProgramMax · 2024-02-16T22:45:11Z

Friendly ping: There are changes requested in order for this patch to land.

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chrisn · 2024-02-19T16:25:38Z

index.html

+          diffuse white as defined in 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>


Suggested change

<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>

chrisn · 2024-02-19T16:25:51Z

index.html

+
+         <p>The following specifies the syntax of the <span class="chunk">dWLn</span> chunk:</p>
+
+         <table id="dWLn-chunk-syntax" class="numbered simple">


Suggested change

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

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

chrisn · 2024-02-19T16:26:02Z

index.html

+         <p>The following specifies the syntax of the <span class="chunk">dWLn</span> chunk:</p>
+
+         <table id="dWLn-chunk-syntax" class="numbered simple">
+           <caption>dWLn chunk components</caption>


Suggested change

<caption>dWLn chunk components</caption>

<caption>dWLm chunk components</caption>

chrisn · 2024-02-19T16:26:48Z

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


Suggested change

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

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

chrisn · 2024-02-19T16:26:58Z

index.html

+         <aside class="example">
+           Example <span class="chunk">dWLn</span> Diffuse white luminance metadata:
+
+           <table id="dWLn-diffuse-white-luminance-metadata-example" class="numbered simple">


Suggested change

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

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

chrisn · 2024-02-19T16:29:52Z

index.html

+           <table id="dWLn-diffuse-white-luminance-metadata-example" class="numbered simple">
+             <tr>
+               <th>Actual value</th>
+               <th>Stored Decimal value</th>


Suggested change

<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)

svgeesus · 2024-02-20T19:05:47Z

index.html

+             <tr>
+               <td>203 cd/m<sup>2</sup></td>
+               <td>203</td>
+               <td>CB 00</td>


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

svgeesus · 2024-02-20T19:14:25Z

We should note that ISO 22028-5 is not a freely available specification. It costs 128 swiss francs. However, it is pretty much an interoperability profile of ITU BT.2100-2 plus a reference display, reference viewing conditions, and mandated MDCV metadata. ISO 22028-5 explicitly does not define what you do with the metadata.

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svgeesus · 2024-02-20T19:24:35Z

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+             </tr>
+
+             <tr>
+               <td>203 cd/m<sup>2</sup></td>


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>

svgeesus · 2024-02-20T19:26:43Z

index.html

+
+             <tr>
+               <td>203 cd/m<sup>2</sup></td>
+               <td>203</td>


Suggested change

<td>203</td>

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

svgeesus · 2024-02-20T19:28:28Z

index.html

+             <tr>
+               <td>203 cd/m<sup>2</sup></td>
+               <td>203</td>
+               <td>CB 00</td>


Suggested change

<td>CB 00</td>

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

svgeesus · 2024-02-20T19:29:21Z

index.html

+             <tr>
+               <th>Actual value</th>
+               <th>Stored Decimal value</th>
+               <th>Stored 2-byte unsigned value</th>


Suggested change

<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.

ProgramMax · 2024-03-04T16:51:38Z

Adding a comment from our meeting today:
The dWLm chunk is for Fourth Edition, not Third. So this pull request is being delayed until Third Edition is wrapped up.
(We could maintain a separate branch but this is the easier path for now.)

ProgramMax · 2024-07-28T03:43:36Z

I think that account is a bot.
Gonna sleep on it then probably delete it's comments.

svgeesus

As noted inline

1. Add dWLm chunk 2. Added ITI BT.2408 reference 3. Added ISO 22028-5 reference

Co-authored-by: Chris Needham <[email protected]>

digitaltvguy linked an issue Dec 10, 2023 that may be closed by this pull request

Add PNG dWLm (Diffuse white luminance metadata ) chunk to conform to ISO 22028-5 #390

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svgeesus marked this pull request as draft January 21, 2024 17:37

svgeesus added this to the Future edition considerations milestone Jan 21, 2024

svgeesus added the registration: new chunk label Jan 21, 2024

chrisn requested changes Feb 19, 2024

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svgeesus force-pushed the 390-add-png-dwlm-diffuse-white-luminance-metadata-chunk-to-conform-to-iso-22028-5 branch from 9f464dc to 9bec304 Compare February 20, 2024 19:19

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added dWLm chunk

e93a3e4

1. Add dWLm chunk 2. Added ITI BT.2408 reference 3. Added ISO 22028-5 reference

svgeesus force-pushed the 390-add-png-dwlm-diffuse-white-luminance-metadata-chunk-to-conform-to-iso-22028-5 branch from 9bec304 to e93a3e4 Compare August 13, 2024 04:06

svgeesus and others added 4 commits August 13, 2024 07:07

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Co-authored-by: Chris Needham <[email protected]>

svgeesus and others added 3 commits August 13, 2024 07:08

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Co-authored-by: Chris Needham <[email protected]>

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Co-authored-by: Chris Needham <[email protected]>

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added dWLm chunk #391

added dWLm chunk #391

digitaltvguy commented Dec 10, 2023

ProgramMax Dec 10, 2023

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ProgramMax commented Mar 4, 2024

ProgramMax commented Jul 28, 2024

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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>


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

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

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

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

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

added dWLm chunk #391

Are you sure you want to change the base?

added dWLm chunk #391

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digitaltvguy commented Dec 10, 2023

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