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Re: What is SVG?

From: Wendy A Chisholm <wendy@w3.org>
Date: Tue, 31 Oct 2000 16:24:58 -0500
Message-Id: <>
To: Anne Pemberton <apembert@crosslink.net>, Web Content Accessibility Guidelines <w3c-wai-gl@w3.org>

"Raster graphics" is defined at: 

"Vector graphics" is defined at: 

Therefore, please reread the section of "Accessibility Features of SVG" 
where it gives an example of a raster-based image versus a vector-graphic. 

Note how the raster-based image (the PNG figure) of the tiger starts to 
break up as it is enlarged while the SVG figure remains smooth.

Because instructions on how to draw the image rather than pixel values are 
sent to the browser, the browser can make the necessary changes when the 
user wants to increase the size of the image.

The boon for accessibility is that you can include text in SVG.  Thus, if 
you make a logo that has text in a funky font, the user can increase the 
size of the image and it will remain readable.  Also, since you are sending 
instructions to the browser you are sending markup.  Within those 
instructions (markup) you can include lots of information about the 
image.  This gets really interesting when you have a diagram or a chart and 
a bar in the chart means something (e.g., bar #1 = how many books were sold 
at amazon.com this june vs bar #2 = how many books were sold in july).  If 
done well, I could navigate the image and grab this information as I go.

Do you see the difference and the benefits to accessibility?

At 10:20 AM 10/31/00 , Anne Pemberton wrote:
>         Checked out both sites, and couldn't find an example of what SVG 
> does.
>Lots of verbage, but no "let me see" ... There is a comparison of a graphic
>in png and svg, which shows svg enlarged nicely next to a png that was too
>small to increase. But the alt tag for the enlarged graphic was "enlarged
>svg", and provided no further information on the graphic. What am I
>missing? Nothing I did on the small svg graphic caused it to enlarge.
>     Further, although I've seen png somewhere in my graphics tools, it
>isn't a format I use. I use mostly jpg and sometimes bmp (reduced to jpg).
>Neither of these were mentioned.
>     As best I could tell, the only difference between jpg and svg is that
>svg lets you do "something" with a description, but I couldn't see an
>example of what that "something" is. Is it there, and I didn't look long
>enough at the site? (I hate horribly long pages that have to include a
>table of contents!)
>Seems it's a long way to go to insure that graphics get alt tags, and a way
>fraught with better choices to do the same thing...
>                                         Anne
>PS: I'm not a math or an art major and have no idea what the difference
>between vector graphics and raster graphics is ... couldn't get even a
>pinch of a clue by reading the information.
>At 11:19 AM 10/31/00 +1100, Jason White wrote:
> >SVG is a graphics format currently under development by W3C. See
> >http://www.w3.org/Graphics/SVG/ for further details, including the
> >excellent note entitled Acessibility Features of SVG:
> >http://www.w3.org/TR/SVG-access/
>Anne L. Pemberton
>Enabling Support Foundation

wendy a chisholm
world wide web consortium
web accessibility initiative
madison, wi usa
tel: +1 608 663 6346
Received on Tuesday, 31 October 2000 16:15:51 UTC

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