Re: [filter-effects] feBlend filter (was: Re: [css-filters] feBlend filter)

On Wed, May 29, 2013 at 7:14 PM, Dirk Schulze <dschulze@adobe.com> wrote:

>
> On May 29, 2013, at 6:59 PM, Rik Cabanier <cabanier@gmail.com> wrote:
>
> >
> >
> > On Wed, May 29, 2013 at 5:33 PM, Dirk Schulze <dschulze@adobe.com>
> wrote:
> >
> > On May 29, 2013, at 5:05 PM, Rik Cabanier <cabanier@gmail.com> wrote:
> >
> > [snip]
> > > If we replace the formulas with the one without compositing, what
> would it mean for blending two intermediate results?
> > > The result would exclude compositing completely. It is unclear how
> this can be done.
> > >
> > > You'd have to explicitly call feComposite on the blended result.
> >
> > feComposite uses the alpha channel of the two input primitives. feBlend
> the same, just that you loose the alpha channel on the result of your
> feBlend (since the state is unclear).
> >
> > Why would you lose the alpha channel? Blending doesn't affect source
> alpha (αr = αs)
> >
> > If the next primitive after feBlend is feGaussianBlur, what would be
> blurred on the alpha channel? I do not think that you can easily separate
> blending from compositing inside a SVG filter tree.
> >
> > Sure you can. feGaussianBlur would work the same except that the source
> colors are now blended and alpha is unaffected.
>
> If ar = as, why would the alpha channel would not be affected on blurring?


If you do a gaussianBlur, its input regardless of it's blended or not, will
always have the same alpha values.
A good question is if blurring after blending makes sense of course :-)