W3C home > Mailing lists > Public > public-html@w3.org > April 2009

RE: Example canvas element use - accessibility concerns

From: John Foliot - WATS.ca <foliot@wats.ca>
Date: Sat, 25 Apr 2009 18:52:36 -0700
To: "'Ian Hickson'" <ian@hixie.ch>
Cc: "'HTML WG'" <public-html@w3.org>, "'W3C WAI-XTECH'" <wai-xtech@w3.org>
Message-ID: <01f301c9c611$aca57cc0$05f07640$@ca>
Ian Hickson wrote:
> In the case of the example above, I'm both the author and the reader.

You are but one reader - I for example, am another.  Thus any generalization
about 'readers' quickly becomes subjective opinion, unless you have no
intention of sharing that content beyond your desktop.
> > You yourself are not a blind user, so how do you know what any blind
> > user might want, never-mind all blind users?
> This isn't only about blind users. It's about users who can't use the
> image. I am such a user on a regular basis, as I use various text-mode
> browsers.
> (Obviously, though, each user may have different desires.)

Correct.  However, based upon your perspective of a sighted user who uses a
text only browser with frequency, you appear (to me) to be invoking your
perception into the spec unevenly.  Specifically I point to your verbose
@alt values, both in this example as well as examples in the current draft
specification.  However countless others have noted on numerous occasions
that when it comes to images, many (most? all?) non-sighted users wish to
choose between a verbose or terse description, similar to 'glancing at an
image' vs. 'studying an image'.  This is an important distinction which
seems to be lost here.

> > Thing is, the author didn't provide text, he provided an illustration
> > (parsing-model-overview.png).
> Actually in this particular case the author wrote the text then wrote
> the illustration to replace it. (I know, it was me.)

C'mon Ian - one example cannot be grounds for a specification.  You can
argue that in this particular instance you may in fact be accurate, but how
many 'parsing model overview' images are there on the web?  It is very easy
to craft an exception to any rule. However, I again refer to the obvious -
if the information could most fully be described as text, why are you using
an image?  As a self-identified text-only browser user, it would seem that
the use of an image here was of little consequence to you if the image was
only intended for you alone (as both author and reader).  However, both you
and I know that the image is conveying a more complex concept, and that it
is intended for an audience greater than Ian Hickson, so let's be honest. 

> > So the image then is more likely a flow chart, or a Venn diagram or
> > something similar to that - and that is legitimate, but introduces an
> > aspect beyond simple text representation as it is a more complex
> > visualization.
> How so?
> The image is the one in the spec:
>    http://www.whatwg.org/specs/web-apps/current-work/images/parsing-
> model-overview.png
> It really doesn't convey any more than the text given above.

Then why are you using an image?  The fact that there is an image here is
significant: it is included for a reason beyond demonstrating your graphics
application prowess - you know it, I know it, and most readers of this know
it as well.  Stop being coy. (or are you suggesting that your document can
exist without that image? Are you prepared to remove that image from the
document then based upon that certainty? You can't have it both ways)

> > So, to solve the 'problem', I would likely go with:
> >
> >    <p>In the common case, the data handled by the tokenization stage
> >    comes from the network, but it can also come from script.</p>
> >    <img src="images/parsing-model-overview.png" alt="flow chart
> illustrating
> >    the parsing model overview"
> longdesc="parsing_model_overview.html">
> >    <p>The network passes data to the Tokeniser stage, which
> >    passes data to the Tree Construction stage. From there, data goes
> >    to both the DOM and to Script Execution. Script Execution is
> >    linked to the DOM, and, using document.write(), passes data to
> >    the Tokeniser.</p>
> As a user who regularly has to view the Web without images, I assure
> you that I would find this significantly less useful and more annoying
> the second example above.

Oh, so the specification is being written then based upon your personal
perspective and annoyance level?  Ian, you constantly talk about use-cases
and 'proof' and examples in the wild - that opinion alone is not sufficient.
Yet because you consider a brief descriptor of an image coupled with an
optional longer, verbose text potentially annoying to you, you dismiss it as
non-viable?  Outside of your personal experience, do you have any proof that
the majority share your opinion? 

While not 'conclusive', WebAIM's survey results (and interpretations) of
screen reader users state:
"The tendency toward the briefer alternative [text] also increased slightly
with screen reader proficiency"

Given those findings, I will suggest my 'opinion' is based upon more than my
personal preference, and seems to directly contradict your opinion.  I leave
it to others to reach a conclusion on who is likely more 'right'.

> As a text-only reader, I really *do not care* that there is an image
> here.
> The image doesn't add anything to the discussion; calling attention to
> it
> feels like the author laughing at me for not being able to see images.
> It
> frankly feels rude.

Enough!  Your personal perspective, while certainly valid for you, is but
one perspective. You keep taking me and others to task whenever we invoke
'feeling' or 'opinion' so please, stow yours at the door as well.  

I ask all non-sighted readers of this exchange to respond specifically to
this allegation: Do you/would you find the example of an image with a
brief/terse description of the image coupled with a longer description
(available upon demand) rude?  Does it 'feel' like the author is laughing at
you?  Or instead, does it feel like the author is respecting the fact that
you may not want every single detail of an image forced upon you - that the
author is instead offering you a choice?

> > (* where parsing_model_overview.html would also attempt to explain
> the
> > visualization in greater detail than the subsequent on-screen text
> > provides)
> I'll grant you that some images might benefit from a separate
> treatment,
> though in practice in fourteen years of browsing the Web I can still
> count
> the number of images I've seen with such treatment on the fingers of
> one
> hand, so I don't think it's worth providing a dedicated feature for
> (all
> such descriptions in fact are just as useful for sighted users and thus
> <a
> href=""> handles them quite adequately). And that's even with my having
> specifically done extensive research looking for such descriptions.
> However, in this particular case, I really don't see what such a
> description could possibly add.

Choice!  The choice between knowing that the image exists vs. a full
understanding of the image.  Why do you presume that this choice is not
important, or do you just not see this distinction?

> > The education piece of the spec (and I grant that you have spent time
> > working on that, and that is a good thing) needs to also point out
> that
> > images are not the appropriate place to be putting large blocks of
> > critical text - something that WAI has been saying for close to a
> > decade.
> Sometimes, images are just the best way to convey something.

Best? Perhaps.  Only? No.  

> Consider,
> for
> example, Feynmann diagrams. It would be inappropriate to require the
> Web
> to convey information only in the least-common-denominator medium
> simply
> because a minority of users are unable to use the best medium.

Agreed, however it is also inappropriate to ignore that minority simply
because they are a minority, especially when there is a means to address
them as well. 

However, consuming information in a fashion similar to drinking from a Fire
hose is also inappropriate.  We know full well that screen readers will
query a page's headings to quickly 'scan' a document, or that they also will
query a page's links to quickly find what they are looking for - these
behaviors indicate that like their sighted friends, non-sighted web users
want to quickly assess a page rather than read it in word for word, detail
by detail. (This 'consumption model' has been studied and documented
extensively by usability experts such as Jakob Neilson to the point where it
can be considered extremely credible).  Recognizing this fact then further
lends credence to my assertion that overly verbose @alt text is less
appropriate and likely unwelcome my the majority - certainly at first pass.

> Similarly, some situations, such as a blind person uploading their
> photos
> for their friends to describe to them, have nothing _but_ a visual
> representation. So it would make no sense to suggest using text
> instead.

This assertion is based upon what? Opinion again?  I know for a fact that my
friend Gregory Rosmaita posts photos to his web-page - I wonder aloud what
he would have to say about this.  It strikes me that in the beginning, some
'generic text' (photo #3826) as a placeholder would allow him to track the
image, and then once his friends have provided a 'better' description he
could replace the placeholder text with the better description.  What in
this scenario does not make sense?

> Rather, we encourage authors to provide textual alternatives where
> possible.

Right, and while we all generally agree that this is a good start, some of
us feel that 'encouragement' alone is not enough. I don't think that this
statement comes as a surprise to anyone who has been following this issue.

> > Our best understanding at this time is that the majority of daily
> users of
> > screen reading technology generally prefer terse descriptions of
> images on
> > first pass
> Really? They prefer terse descriptions of images to just self-contained
> text with no images at all? This seems to run counter to what you've
> been
> saying up to this point.

Then you clearly are not understanding what I am suggesting.  Let's try it

1) Based upon WebAIM's survey results, and upon numerous conversations I
have had with non-sighted users, I am stating that when an 'important' image
is used in an html document, most non-sighted users appear to prefer a brief
description of the image in the @alt value, versus an overly verbose
description such as you have suggested both in this email thread and in some
of the examples posted in the current HTML 5 draft. 

2) I have compared this to approximating the difference between glancing at
a photo versus an in-depth studying of an image, options that you, as a
sighted user have on a daily basis (and in fact likely take for granted,
although I cannot state that for a certainty in your personal instance). 

3) I believe we are in agreement that a means to provide a more verbose
description to an image is useful, be it @longdesc (appropriate if
misunderstood and misused) or the newer and perhaps more scalable ARIA

4) Finally, I believe that I have been both adamant and consistent in this
position from the beginning and if it has not been clear, hopefully it is

Received on Sunday, 26 April 2009 01:53:33 UTC

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