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Re: Is longdesc a good solution? (was: Acessibility of <audio> and <video>)

From: Robert J Burns <rob@robburns.com>
Date: Mon, 8 Sep 2008 17:51:49 +0200
To: James Craig <jcraig@apple.com>
Message-Id: <6A88FBE5-B25B-4F98-889C-C8359BBADBFF@robburns.com>
Cc: John Foliot <foliot@wats.ca>, Lachlan Hunt <lachlan.hunt@lachy.id.au>, wai-xtech@w3.org, public-html@w3.org

Hi James,

On Sep 8, 2008, at 3:56 AM, James Craig wrote:

> John Foliot wrote:
>> Lachlan Hunt wrote:
>>> It has been suggested to me that there may be cases where an image
>>> needs to have a description and provide a link elsewhere, which  
>>> would make
>>> this solution unusable. But no-one has yet been able to provide a
>>> valid use case illustrating that.
>> OK, here you go: http://www.nasa.gov/
>> The main page has a picture of the shuttle Atlantis, with the not  
>> so great
>> alt text of "STS-125 Atlantis". However, the photo is actually quite
>> complex, and so could benefit from a longdesc (although sadly it  
>> does not
>> exist).  Clicking on the image takes you to the section or the Nasa  
>> site
>> concerning the Atlantis shuttle.
> In this case, no long description is needed. Certainly better alt  
> text should be there, but the point of the image is adequately  
> described by the title ("Shuttle Atlantis at the Launch Pad, Set for  
> Hubble Mission") and the caption ("Atlantis' crew, targeted to  
> launch on Oct. 10, will upgrade the Hubble Space Telescope,  
> extending the life of the groundbreaking observatory. [link] Hubble  
> Servicing Mission, [link] Space Shuttle Section").
> It is irrelevant that the image contains two photos from different  
> perspectives and a graphic of the mission patch. It some respects,  
> it may even be considered a decorative image. All three of those  
> main sections contain large images that are intended to get the  
> viewer to click through to the related article, the images are not  
> there for their own sake.
> Sometimes overly-detailed accessibility is championed at the expense  
> of usable accessibility. Consider how often you "skim" content  
> sections. Blind people don't want to be bogged down by minutia any  
> more than sighted users do.
> When @longdesc was the best solution, I argued that it should only  
> rarely be used, specifically in the case of charts and graphs, where  
> data visualization represents real page content that requires a  
> longer explanation than @alt will allow.
> Even image galleries (such as Flickr or a museum website) should  
> rarely, if ever use longdesc. Yes, the main point of the content is  
> the image itself, but that content should be described on the page.  
> In the case of artwork, this usually provides benefit to non- 
> disabled users, too. Imagine an image's in-page, visible long  
> description provides detailed discussion of the artist's intention  
> in his choice of color, and the form contrast or dynamic angular  
> motion of the painting.
> This kind of detail enlightens all viewers, and it doesn't need to  
> be visible by default. The web comic, Penny Arcade (It may have been  
> a different comic), used to have a drop-down section of the page  
> that had a data table listing characteristics of each pane,  
> including which characters were visible, the dialog, and any  
> background information including links to events or jokes in  
> previous strips that may have been missed by anyone but a regular  
> reader. Though not initially visible, this information was useful  
> for numerous reasons.
> 1. It increased the accessibility for blind readership.
> 2. I, for example, didn't know most of the character's names, so I  
> could learn them by looking in the "long description" section.
> 3. Google could more accurately index the content of each page, so  
> people could search for content by a phrase they remembered.
> 4. etc.
> All without the use of longdesc.
> The "Visual Complexity" gallery <http://www.visualcomplexity.com/vc/ 
> > has loads of examples where, in its original context, each graph  
> or chart should probably have had used longdesc. On the VC site  
> however, even though the images are charts and graphs, longdesc is  
> not required because each item's page discusses the artistic data  
> visualization technique used, and in the context of the gallery, the  
> detail of the data itself is irrelevant.

I think these are good examples. However, your reminder that alt text  
should be short raises the question of where an author puts other  
information about embedded images if they want to provide more than  
just alt text (which should tend to be fairly brief). The longdesc  
attribute has traditionally provided a mechanism for other text  
equivalents (other than alt text).  So in this case, while a user does  
not necessarily need to know what image leads them to the next page in  
a site, they may be curious and want to query their UA to find out  
more details. I can't imagine why we wouldn't want to continue to  
provide a mechanism for this type of fuinctionality (whether it is the  
longdesc attribute or something else).

Take care,
Received on Monday, 8 September 2008 15:52:54 UTC

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