Re: [csswg-drafts] [css-images-3] clarification on metadata position in specific file formats (#8543)

The CSS Working Group just discussed `[css-images-3] clarification on metadata position in specific file formats`, and agreed to the following:

* `RESOLVED: Don't require metadata at the start if the format doesn't allow it`

<details><summary>The full IRC log of that discussion</summary>
&lt;emilio> chris: we have a requirement for metadata to be placed before some image formats<br>
&lt;fantasai> s/pass CR criteria/pass CR criteria and apply to HTML elements specifically,/<br>
&lt;emilio> ... except in some formats that's invalid<br>
&lt;miriam> q?<br>
&lt;emilio> ... I propose the spec that says that if there is a choice in the image format then put that before<br>
&lt;TabAtkins> +1<br>
&lt;florian> q+<br>
&lt;emilio> Proposed: Only ask for metadata before if that's acceptable<br>
&lt;miriam> ack florian<br>
&lt;emilio> florian: what we proposed is clear for what authors are supposed to do<br>
&lt;emilio> ... the other one is a requirement for UAs to ignore metadata-after-data<br>
&lt;emilio> ... so what's the proposal for that?<br>
&lt;emilio> chris: that is a different issue, we have different behavior<br>
&lt;emilio> ... e.g., webp metadata is ignored in some implementation<br>
&lt;emilio> ... if you have a giant webp that rotates the image at the end it seems bad<br>
&lt;emilio> florian: spec currently says SHOULD, should it be MUST?<br>
&lt;emilio> chris: yes<br>
&lt;emilio> Proposed: Only ask for metadata before the data if that's acceptable for a file format<br>
&lt;emilio> Proposed: Don't require metadata at the start if the format doesn't allow it<br>
&lt;dbaron> WebP also apparently doesn't offer progressive decoding<br>
&lt;emilio> RESOLVED: Don't require metadata at the start if the format doesn't allow it<br>
&lt;emilio> Proposed: UAs must not honor metadata at the end of the file<br>
&lt;florian> proposed: ignore layout affecting metadata when it is after the data, even in file formats where there is no choice<br>
&lt;emilio> myles: not sure if that's implementable<br>
&lt;emilio> q+<br>
&lt;emilio> emilio: dbaron pointed out that webp doesn't support incremental decoding<br>
&lt;emilio> myles: right, if no incremental decoding is fine to have metadata at the end<br>
&lt;florian> q+<br>
&lt;emilio> ... seems more of a quality of implementation issue<br>
&lt;astearns> proposed: if you have started progressive rendering, you SHOULD ignore subsequent layout affecting metadata<br>
&lt;emilio> ... I don't think ignoring the metadata should be a requirement<br>
&lt;emilio> ack emilio<br>
&lt;emilio> myles: I think I'm proposing no resolution at all<br>
&lt;emilio> ... then we can outreach PhotoShop or something to prefer metadata at the front or what not<br>
&lt;miriam> ack florian<br>
&lt;emilio> florian: I don't have that strong opinion on whether ignoring metadata<br>
&lt;emilio> ... but having a should and browsers doing different things is bad<br>
&lt;emilio> myles: I think we should remove that should from the spec<br>
&lt;miriam> ack dbaron<br>
&lt;emilio> dbaron: it's probably worth having something like what astearns proposed<br>
&lt;emilio> ... even if it's a may<br>
&lt;emilio> myles: that's worse right? You end up with the wrong orientation in one browser but not the other<br>
&lt;emilio> ... we probably want the same images to look the same once everything is loaded<br>
&lt;emilio> astearns: Not certain it's a terrible thing to have different behavior here<br>
&lt;emilio> ... you still get the image data and is flipping<br>
&lt;emilio> dbaron: if we are going to switch the spec we should have the data on what different implementations do<br>
&lt;dbaron> s/spec/spec from must or should for one thing to its opposite/<br>
&lt;emilio> florian: what about text that say that if the UA can't ignore metadata it can't ignore it in some cases but not in other<br>
&lt;emilio> ... I think I agree with myles that once the image loads it all should be the same<br>
&lt;emilio> miriam: should we take this to the issue / or a different issue?<br>
&lt;emilio> myles: sure<br>
</details>


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Received on Thursday, 14 September 2023 08:48:06 UTC