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Re: image links and (text)boxes

From: Charles McCathieNevile <charles@w3.org>
Date: Mon, 16 Dec 2002 07:55:31 -0500 (EST)
To: Jonathan Chetwynd <j.chetwynd@btinternet.com>
cc: WAI GL <w3c-wai-gl@w3.org>
Message-ID: <Pine.LNX.4.30.0212160730090.10483-100000@tux.w3.org>


First, a general commment - you are trying to do some serious graphics work
here, and I think the first conclusion is that HTML is not a language for
serious graphics. You can embed complete objects in HTML that are, such as
Flash or SVG, but you are working at the bleeding edge of Web technology, and
that means some things aren't yet as easy as they will be when the tools are
better-developed and more widely deployed.

In fact if you use SVG as the basis you should be able to embed XHTML inside
it, but this is pushing the current state of deployed technology pretty hard.

SVG does give you reasonable file size, ensures that the scaling of images is
as high-quality as possible. For all-svg image, such as line-drawings,
digrams and icons it does very well. For photo-real images it is a bit
harder. There is an experimental project in France to convert photographic
images to SVG using gradients, but this is prototype work. Otherwise jpg is
the state of the art, but it doesn't have transparency. You can do that by
including them in an SVG image, and you can then have a border that follows
the outline (in almost any colour or style you like). These will scale as
well as a jpg can scale, because SVG defines a high-quality algorithm
(compared to the way most browsers re-size jps - image editing tools should
do a better job in general of getting to a particular fixed size).

In fact having transparent backgrounds isn't always a good idea, so i think a
guideline that insists on it is a bad idea. What can happen is that the
borders of the 'image content' are the same colou as the  background that
happens to be on the page, meaning you lose the contrast and violate the WCAG
1 checkpoint 2.2 about ensuring adequate contrast.

The insistence on boxes is just an artifact of the way layout engines work -
since HTML wasn't designed to be a high-end graphics language it has the
simplest systems, which are regular rectangles (well, it was once even
simpler and just used strips of the screen at full width, but most browsers
have gone beyond that now...). In languages like SVG there is no such
constraint, although most implementations still require a rectangular space
for the SVG if it is embedded in another format such as HTML. SVG itself,
like most currently used graphics systems, use cartesian coordinates for
addressing points - other systems such as polar coordinates are difficult to
use for general applications, although there are transformations between
cartesian and polar coordinates readily available in high-school maths
classes and text books.



On Sun, 15 Dec 2002, Jonathan Chetwynd wrote:

>the outlines of image links are helpful for identification,
>BBC Education Scotland recently put up some new links, (I had been in
>correspondence) which we now can use....
>Can we make a guideline that image links* should ideally have
>transparent backgrounds, and non-rectangular** outlines?    (W3C please
>and failing on transparency have backgrounds that are easily changed?
>*presumably most sites are happy to be linked to, so why is it that so
>few images used as links are appropriate for sharing?
>**wondering what others feel about the rather heavy handed cartesian,
>or western imperialist insistence on boxes?
>has anyone seen a small (~30x3) text box that expands as you write?
>this should also be a standard by now, at least as an option...
>like this but much better :-)
>  if (myText == "feedback"){
>		var myLength=parseInt(document.myPost.feedback.cols)
>		var myHeight=parseInt(document.myPost.feedback.rows)
>		if (key==13) {                                             //newline
>			document.myPost.feedback.rows=myHeight + 1
>		}
>		if (myLength != 90){                                  //~page width
>			document.myPost.feedback.cols=myLength + 1
>		}

Charles McCathieNevile  http://www.w3.org/People/Charles  tel: +61 409 134 136
SWAD-E http://www.w3.org/2001/sw/Europe ------------ WAI http://www.w3.org/WAI
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Received on Monday, 16 December 2002 07:55:32 UTC

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