Re: ISSUE-2317 (feGaussianBlur stdDeviation=0): Give different result for feGaussianBlur stdDeviation=0 [SVG Full 1.1]

On Fri, 02 Apr 2010 17:49:19 +0200, SVG Working Group Issue Tracker  
<sysbot+tracker@w3.org> wrote:

>
> ISSUE-2317 (feGaussianBlur stdDeviation=0): Give different result for  
> feGaussianBlur stdDeviation=0 [SVG Full 1.1]
>
> http://www.w3.org/Graphics/SVG/WG/track/issues/2317
>
> Raised by: Doug Schepers
> On product: SVG Full 1.1
...
> Opera and Firefox both handle this correctly (according to the spec).  
> But it
> seems to me the spec is a bit too fussy. It is written, I presume, to  
> avoid a
> problem of dividing by zero in the definition of the blur function:
>
> H(x) = exp(-x2/ (2s2)) / sqrt(2* pi*s2)
>
> But when you think of it this way: more standarddeviation means more  
> blur. Zero
> standard deviation should mean no blur.
> The issue arose when I wanted to use script to append a blur filter onto  
> an
> object and allow a slider to control the amount of blur. Rather than  
> removing
> the filter attribute from the DOM I just wanted to change StdDev to  
> zero. Alas,
> while ASV knew what I wanted to do, Opera and FF followed the spec. I  
> think this
> attribute is only used in feGaussian blur, but even if it were used in  
> other
> contexts, I do think that authors will think zero means "no  
> variability", not
> "turn the image black and make it transparent"
>
> Is this the sort of thing that should be raised here, in SVG IG, or with  
> SVG WG,
> or with a nontrivial subset of the three?
> ]]

I agree that it's more intuitive to let stdDeviation="0 0" mean that the  
filter just returns the filter input unchanged (that is: no blur applied),  
and that having e.g stdDeviation="25,0" should mean that the blur is only  
applied in the direction where there's a non-zero value.

I have ACTION-2189 to clarify this in the filters spec.
/Erik

-- 
Erik Dahlstrom, Core Technology Developer, Opera Software
Co-Chair, W3C SVG Working Group
Personal blog: http://my.opera.com/macdev_ed

Received on Tuesday, 6 April 2010 08:27:04 UTC