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Clarify the createImageBitmap orientation metadata handling #11234

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Clarify the createImageBitmap orientation metadata handling #11234

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46322dc
Clarify the createImageBitmap orientation metadata handling
Hajime-san Apr 17, 2025
c86ad9e
Add name to acknowledgements
Hajime-san Apr 17, 2025
ccce7cc
Preface that reflects EXIF metadata
Hajime-san Apr 24, 2025
81d43bf
Separate the steps
Hajime-san Apr 24, 2025
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Separate the steps
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@Hajime-san
Hajime-san committed Apr 24, 2025
commit 81d43bf81f5440f6d43b03acf4c0f709d0c9b264
26 changes: 16 additions & 10 deletions source
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Expand Up @@ -119255,16 +119255,22 @@ dictionary <dfn dictionary>ImageBitmapOptions</dfn> {
choice of scaling algorithm.</p></li>

<li>
<p>Apply the orientation to <var>output</var>, if <var>image</var> is an <code>img</code>
element or a <code>Blob</code> object that contains orientation metadata of the source
such as <ref>EXIF</ref> metadata at first, and if the value of the <dfn dict-member
for="ImageBitmapOptions"><code data-x="dom-ImageBitmapOptions-imageOrientation">imageOrientation
</code></dfn> member of <var>options</var> is "<dfn enum-value for="ImageOrientation"><code
data-x="dom-ImageOrientation-flipY">flipY</code></dfn>", <var>output</var> must be flipped
vertically.</p>

<p class="note">If the value is "<dfn enum-value for="ImageOrientation"><code
data-x="dom-ImageOrientation-from-image">from-image</code></dfn>", no extra step is needed.</p>
<p>If <var>image</var> is an <code>img</code> element or a <code>Blob</code> object that
contains orientation metadata of the source such as <ref>EXIF</ref> metadata, apply the
orientation to <var>output</var>.</p>
<p>Let <var>val</var> be the value of <dfn dict-member for="ImageBitmapOptions"><code
data-x="dom-ImageBitmapOptions-imageOrientation">imageOrientation</code></dfn> member of
<var>options</var>, and then run these substeps:</p>

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You want these to be separate steps.

I also worry a bit that this isn't the right place to do it, but perhaps that can later be more properly abstracted. As we should really decode images in a single place after they come from the network and there we should apply the orientation metadata.
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I also worry a bit that this isn't the right place to do it, but perhaps that can later be more properly abstracted. As we should really decode images in a single place after they come from the network and there we should apply the orientation metadata.

There has been no agreement and this is merely a suggestion and implementation-oriented, but there was a conversation about making createImageBitmap a no-op to make it more tolerant of performance and reference from external specifications such as WebGPU.
As a result, I think it is best to just write down how EXIF ​​is handled for now, so as not to restrict implementation-oriented behavior such as the timing of decoding or storing byte sequences including EXIF ​​as internal variables in the API implementation.

cc: @ccameron-chromium
<ol>
<li><p>If <var>val</var> is "<dfn enum-value for="ImageOrientation"><code
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This is applicable regardless of whether the imageOrientation member is given.
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Got it, I changed to reflect the orientation at first.
data-x="dom-ImageOrientation-from-image">from-image</code></dfn>", no extra step is needed.</p>
</li>
<li><p>If <var>val</var> is "<dfn enum-value for="ImageOrientation"><code
data-x="dom-ImageOrientation-flipY">flipY</code></dfn>", the <var>output</var> must be
flipped vertically.</p>
</li>
</ol>

<p class="note">There used to be a "<dfn><code
data-x="dom-ImageBitmapOptions-imageOrientation-none">none</code></dfn>" enum value. It was
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