If I add a simple UV sphere that emits white light, and in the compositor add a Fast Gaussian blur effect, then when viewing on a transparent background there is a noticeable black halo around the glow.
Any ideas what the correct way to do this is?
Update: It seems to have something to do with the horizon colour being picked up by the blur effect. How do you prevent that from happening? As a work around I can set the horizon colour to white, but I don't think that's the correct way to do it...
Here you can see with a red horizon colour, and changing the colour of the emitter to blue the effect is quite pronounced: