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Re: Proposed adaptive image element

From: Mathew Marquis <mat@matmarquis.com>
Date: Tue, 24 Jul 2012 11:26:40 -0400
Cc: HTML WG <public-html@w3.org>, Ian Jacobs <ij@w3.org>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-Id: <5E3C2751-0FE1-4391-9CFD-230E112A5B00@matmarquis.com>
To: Laura Carlson <laura.lee.carlson@gmail.com>

On Jul 24, 2012, at 7:48 AM, Laura Carlson wrote:

> Hi Mat,
> 
>> With the above in mind I’d love to discuss the next steps in working towards
>> a specification, and keep our momentum up. There was mention of filing a bug
>> to have this proposal officially entered into the WG system — is that our
>> next course of action?
> 
> Filing a bug is step one in the HTML Working Group decision process.
> http://dev.w3.org/html5/decision-policy/decision-policy-v2.html
> 
> With regard to accessibility two things that may be worth consideration:
> 
> 1. The possibility of responsive text alternatives that could parallel
> the responsive images if needed. The <picture> proposal allows for
> different sources for images at different sizes. But authors could use
> different images at different sizes and not just a cropped down
> version of a single image. No text alternative mechanism is provided
> for that use case. Allowing alt on <source> could provide for that use
> case. Something like the following might work:
> 
> <picture>
> <source src="mobile.jpg  alt="text alternative">
> <source src="medium.jpg"  alt="text alternative" media="min-width: 600px">
> <source src="fullsize.jpg"  alt="text alternative" media="min-width: 900px">
> <img src="mobile.jpg" alt="text alternative">
> </picture>
> 

I wouldn’t want to run the risk of encouraging authors to use drastically different sources for an image (in my nightmares I see banners reading “welcome to my website” being swapped for “welcome to my iPhone website” at small sizes). I think it’s worth having it codified that the alternate sources are meant to provide different crop/zoom/representation of a single subject, and one should be able to accurately describe it a single string of assistive text. For example: Jason Grigsby’s example at http://blog.cloudfour.com/a-framework-for-discussing-responsive-images-solutions/#artdirection can still be accurately described by “photo of President Obama speaking at a Chrysler plant.”

I think it stands to reason that `alt` could be specified on `picture`. If the `alt` is omitted from `picture` but specified on the fallback `img`, that `alt` should likely apply to the `picture` element overall. There has already been some discussion around how the `alt` attribute would “cascade,” so to speak, here: http://lists.w3.org/Archives/Public/public-html/2012Jun/0118.html


> 2. A picture element could allow for semantic programmatically
> determinable in-page rich text long description, if a description
> element was added to the proposal:
> 
> <picture>
> <img src="image.jpg" alt="text alternative">
> <desc>structured rich text description with headings, lists, tables, etc.</desc>
> </picture>
> 

I’m very much in favor of this approach, provided that assistive technology would have the ability to “reach into” the `picture` element and access the more descriptive text. Alternately, `picture` is a prime candidate for use within `figure`, so it’s possible that role would be best served be `figcaption` — rather than leaving authors to specify fallback content as an afterthought strictly for a11y purposes, having that content readily available to all users might encourage them — and could be further improved through the use of `aria-describedby`.

There’s similar discussion taking place in parallel on the WHATWG list, here: http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2012-July/036675.html

> Best Regards,
> Laura
Received on Tuesday, 24 July 2012 15:27:10 GMT

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