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RE: high contrast and background images

From: Thierry Koblentz <ng@tjkdesign.com>
Date: Tue, 15 Jun 2010 08:57:15 -0700
To: "'Jonathan Avila'" <jon.avila@ssbbartgroup.com>, <w3c-wai-ig@w3.org>
Message-ID: <05a401cb0ca3$6f6c6b50$4e4541f0$@com>
Hi Jonathan,

> Your point is well taken for images that are not text.  However, I do
> have
> several thoughts.  Since only one image is used, automated testing
> tools
> will need to pull the viewport coordinates from the code to determine
> which area of the larger image is applicable to the current element.
> For
> instance, an automated testing tool displays the whole image when
> needed.

The image has no "footprint". Its width and height values are equal to 0 or
1, plus it has no alt text (alt=""). So imho it should be *ignored* by AT
and automated testing tool as well. Legacy documents are littered with
"spacer" images so I'd say it makes sense to ignore such small images
> In the example from
> http://tjkdesign.com/articles/how-
> to_use_sprites_with_my_Image_Replacement
> _technique.asp text is used since this is a heading where text fits.
> However, many sites that use this technique will likely use icons where
> there is not sufficient room to place on-screen text without messing up
> the layout.  In those cases alt text would need to be applied to the
> image
> and I'm sure some developers won't do this.  When an automated tool
> detects the missing alt text it will display the entire image for the
> user
> to review to determine what the appropriate alt text is.

We are talking Image Replacement Techniques, so we do have text in place.
That text is off-screen with most techniques relying on background images,
but it is in view when images are off with techniques relying on <img>.
Imho, adding alt text would create redundancy.
It is true that for small icons the problem is still the same as the text
could appear truncated, but this is not related to the high-contrast problem
discussed here. It is a general issue that could be better addressed by
sniffing for images support and serving a text version(?).

> The example also uses a lot of fixed pixel coordinates.  I am unclear
> if
> relative sizing can be used effectively with this solution.

This is an example using EMs: http://tjkdesign.com/articles/tip_5.asp

www.tjkdesign.com | www.ez-css.org | @thierrykoblentz
Received on Tuesday, 15 June 2010 15:57:41 UTC

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