On Tue, 11 Mar 2003 20:05:39 +0100, "Steinar H. Gunderson" <[EMAIL PROTECTED]> wrote:
> On Tue, Mar 11, 2003 at 10:15:51AM -0800, Daniel Rogers wrote:
> > Alpha is a measure of the amount of coverage of the pixel.  (e.g. an 
> > alpha of .5 means half the pixel is covered).  In particular, 0 alpha 
> > means that the pixel is not covered at all.  This means that the pixel 
> > contributes NO color information.  I think this should hold for blur as 
> > well.  And from that point of view, no pixel with alpha zero should ever 
> > contribute color information.
> How do you propose this being implemented, ie. what value would you plug into
> the IIR filter GIMP's blur is based on, for a pixel with alpha != 255?

You would not plug any color there, of course.  Or more exactly, the
color would not matter because it would be multiplied by 0 anyway.

Please take a look at the formulas in these two bug reports:

The IIR Blur filter was also affected by that bug but it has been fixed
thanks to David Necas (Yeti):

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