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Re: Assumption in the SVG specifications

From: Chris Lilley <chris@w3.org>
Date: Thu, 31 Aug 2006 15:13:32 +0200
Message-ID: <708494942.20060831151332@w3.org>
To: Dave Singer <singer@apple.com>
Cc: www-svg@w3.org

On Thursday, August 31, 2006, 2:19:20 PM, Dave wrote:

DS> At 13:22  +0200 31/08/06, Chris Lilley wrote:
>>On Thursday, August 31, 2006, 12:58:32 PM, Dave wrote:

>>DS> It seems that the SVG specifications assume that SVG is the only
>>DS> vector format in existence.  Quoting one of the specs on the site:

>>DS> "In SVG Tiny 1.2, the 'image' must reference content that is a raster
>>DS> image format, such as PNG and JPG. SVG Tiny 1.2 does not allow an SVG
>>DS> document to be referenced by the 'image' element; instead, authors
>>DS> should use the 'animation' element for referencing SVG Documents."

>>DS> and

>>DS> "The 'animation' elements specifies an SVG document providing
>>DS> synchronized animated vector graphics. "

>>Thats an error. Indeed it was already discussed, and we agreed that 
>>the animation element is for general animated vector graphics 
>>(although a conformant viewer is only required to render the 
>>contents if they point to SVG).

>>It seems that wording did not get updated; we will fix this error.

>>DS> Could someone clarify if the intent of this specification was to
>>DS> exclude the use of all other possible static vector formats?

>>No, that was not the intent. The conformance requirement and the 
>>intent of the element were conflated in the text you cite; these 
>>will be clearly separated.

DS> Chris, thanks

DS> this helps, but I want to be clear.  The "animation" element is 
DS> supposed to be used for any vector-based content, even if the format 
DS> doesn't permit any animation as such, or the image in question is 
DS> not, in fact, animated?

DS> I think there is a deeper problem here.  The tags 'image', 'video', 
DS> and 'audio' ask these questions about the content
DS> a) does it have a visual presentation?
DS> b) does it have an audible presentation?
DS> c) does the presentation change over time?

DS> whereas the 'animation' tag seems to ask a completely orthogonal question
DS> i) is it coded using vectors or rasters?

In fact the image element also asks that, in 1.2.

DS> The first three questions enable the client to know 'does it use 
DS> screen real-estate?', 'do I need to connect to an audio output 
DS> device?' and 'do I need to manage the content handler providing a 
DS> visual presentation that changes over time, might the user want 
DS> (perhaps) at least a play/pause control?'.  They are all questions 
DS> about how the content is *presented*.  The animation tag seems to be 
DS> asking about how it is *coded*, by contrast, and not surprisingly, 
DS> this raises questions.

Once could phrase it as 'do I need to set up a nested viewport' and, for Fullbut not Tiny, 'do I need to clip content outside that viewport'.

Raster images, in general, do not have content outside their width and height. By definition. They are also not timed elements (this means that MNG, animated GIF, etc would go on a video element, incidentally).

DS> I have to say I am quite surprised that the answer to the question 
DS> "what tag should I use to display an illustrator image" is not 
DS> "image" but "animation", but that the answer would change if I 
DS> rendered the image *to the same visual quality and effect* to a PNG 
DS> file and then embedded that (the user should be able to detect no 
DS> difference at all).




-- 
 Chris Lilley                    mailto:chris@w3.org
 Interaction Domain Leader
 Co-Chair, W3C SVG Working Group
 W3C Graphics Activity Lead
 Co-Chair, W3C Hypertext CG
Received on Thursday, 31 August 2006 13:13:57 GMT

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