Gaussian Blur with very small stdDeviation

I have a question about the correct behavior of the Gaussian Blur filter 
when a very small stdDeviation is used.  The 1.1 SVG specification 
suggests using 3 box blurs with a size given by:
boxSize = floor (s * 3 * sqrt( 2 * pi) / 4 + 5)
in order to approximate a Gaussian Blur for s >= 2.0.  I am curious if 
anyone has some suggestions about how to handle the case when s < 2.0. One 
might be tempted to just assume the effect of the blur with a low value 
for s to be negligible, but such is not the case.  The following code 
shows an (extreme) example in which the light blue circle is blurred with 
a stdDeviation of 0.001 and scaled to a size where the blurring effect is 
noticeable (when rendered in Opera9beta, Batik, or IE Adobe plugin).  The 
yellow circle shows what an unblurred edge looks like for comparison. 


<svg xmlns:xlink="" 
    <filter id="smallBlur">
      <feGaussianBlur in="SourceGraphic" stdDeviation="0.001"/>
  <circle cx="0" cy="0" r="1" fill="lightblue" filter="url(#smallBlur)" 
  <circle cx="0" cy="0" r="1" fill="yellow" transform="scale(1100)"/>

Received on Monday, 26 June 2006 21:58:39 UTC