Federico Mena Quintero wrote:

> And yes, the blend tool should do the right thing with alpha values,
> i.e. premultiply them before compositing them in.  I'll submit a patch
> for it in the afternoon.

I don't think this episode uncovered an alpha-related bug, so what needs to be fixed?

Mr. Turner's example (unwittingly, perhaps) specified two different gradients (in the 
color space). And two different results were obtained. What went wrong?

*Should* the gradient tool work in the premultiplied space, while GIMP mostly functions
in the unmultiplied one? Won't this give users different alpha characteristics in 
different places?
Won't they be better served with a consistent alpha channel behavior of the 
space in *most* places? Especially since - for better or worse - the rendering 
pipeline functions
with unmultiplied alpha only? The gaussean blur HAS to pull premultiplied tricks. No 
there either, for just as Mr. Lamb observed with premultiplied alpha, the unmultiplied 
space is
no cure for the blues either. They happen to be two (mutually exclusive) conventions 
that can
be applied to the alpha channel, and one has a Real Slick compositing algorithm 
associated with
it, blessed by the Computer Graphics Gurus.

In light of this, then, I think we should be very careful in preserving a consistent 
behavior when
it come to how the alpha channel behaves, and warn users when inconsistencies 

Be good, be well.


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