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Re: Images and alternative text

From: Smylers <Smylers@stripey.com>
Date: Sat, 9 Aug 2008 13:33:46 +0100
To: public-html@w3.org
Message-ID: <20080809123346.GG11746@stripey.com>

Philip TAYLOR (Ret'd) writes:

> Ian Hickson wrote:
>
> > On Thu, 7 Aug 2008, Philip Taylor wrote:
> > 
> > >   <img src="..." alt="{x \over y} = {1 \over {y \over x}}">
> > 
> > ...would be a horrific alternative text to give a screen reader.
> > 
> > I don't think it's equivalent to the image at all. It's the source
> > of a program that was used to generate the image, but that's not the
> > same thing. 
> 
> It /may/ be the source of a program, but far more importantly it is an
> internationally recognised way of conveying the meaning of the image
> in a linearised fashion.

Boris Zbarsky writes:

> in some communities sending TeX as part of your text message is
> considered perfectly reasonable, at least for simple equations.  So a
> lot of people don't think of it as "source code" but as simply another
> notation, one well-suited for plaintext communication.

John C. Vernaleo writes:

> I just don't see how the textual representation of equations  scales
> very well past very simple equations.  Even in the example here  that
> sentence is just barely unambiguous.  A more complex equation would be
> much worse and a matrix basically impossible.  And I'm not convinced a
> human could do it any better than a program could.
>
> At least the version that was close to the LaTeX code still contained
> the relevant information in a way that is mostly parsable by a human.

I don't speak Tex, but I'm not the kind of person who often reads
webpages with equations on them.  Of my mathsy friends, the ones who do
encounter equations on a regular basis, they do speak Tex.

So I agree that for some pages' target audiences, when a non-graphical
way is needed of conveying equations, Tex is likely to be the best
language for doing so.  On other pages Tex may be inappropriate, and
other alt text should be chosen.

Is this just one field's instance of a situation that occurs in other
fields?  For example, suppose an image was the musical notation to play
a tune, would the best alt text be something like:

  In the key of D in 4/4 time, play the A above middle-C for a crotchet,
  then 2 B quavers, then D minim ...

Or is there a more succint textual notation?

What about patterns for printed circuit boards?  The representation of a
chess board at a particular instant mid-game?  Crossword grids?  Sudoku
puzzles?

And, if there is a generalized scenario here, does HTML 5 need to take
it into account?  Does it merit an entry in the list of types of images
for working out what the appropriate alt text is?  I think not, because
it's already covered by one of the existing ones; but it may be worth an
example, blessing this as suitable behaviour.

T.V Raman writes:

> And what's more, you can reliably transform the LaTeX markup to any
> number of different alternative representations -- that makes the
> LaTeX a far more useful form of alternative information than any
> single textual description.

You can only do this if the text not only is Latex, but also is marked
as such.

Would it be useful to provide authors with a way of conveying 'the alt
text on this image isn't human language, but notates in language $Foo
the same thing as the image represents graphically'?  In practice, how
would such information be used by user-agents?

Smylers
Received on Saturday, 9 August 2008 12:34:32 UTC

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