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Re: Speed on Animated Gifs

From: Charles McCathieNevile <charles@sidar.org>
Date: Wed, 14 May 2003 11:18:48 +0200
Message-ID: <3EC209F8.4000906@sidar.org>
To: James Little <james.little@onetel.co.uk>
CC: w3c-wai-ig@w3.org

There are two issues with animation. The most serious is photo-sensitive 
epilepsy, which means that things which blink in a range between a 
couple of times a second and 50-odd times per second can cause people to 
suffer a seizure - effectively a serious health risk, as well as being a 
very poor customer experience.

The other issue (which is the one that effects me, for example) is 
distracting people - some people simply cannot read content around a 
flashing image. Fortunately we can now get browsers that will just turn 
the animation off, but if there is something important in it we need to 
see it through first - the text alternative is not typically displayed 
alongside the image in a graphic view. (I know some people like "access 
Bob" use lynx all the time to deal with the problem - I use a mix of 
browsers depending on where i am and what I am doing - most airports 
have IE available but it is harder to find a lynx terminal).

So my advice is to make it have at most 2 frames per second, and if 
possible go slower. You might also like to consider an animated vector 
format such as flash or SVG (I would only use SVG for lots of reasons, 
but flash can be made to do the job and you can provide 
"(nearly)-equivalent" alternatives for either case). They will give you 
smooth animation, and you can work especially with SVG using lots of 
neat XML tools to do things like auto-generate XHTML equivalents...



 (See Web Content Accessibility Guidelines, guideline 7 - 
http://www.w3.org/TR/WCAG10/wai-pageauth.html#gl-movement - for some 
more info)

James Little wrote:

>Does anyone know if there is an acceptable "time" between frames on
>Animated Gifs?  I have one that needs to go on a site that I develop,
>but I don't want to break 3.7.1 and 3.7.2 ("Flickering, flashing and
>blinking should be avoided or at least
>I heard somewhere that there was an acceptable amount of time, but I
>can't remember exactly what it is.
Received on Wednesday, 14 May 2003 05:19:27 UTC

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