Communigate Pro AE-List@media-motion.tv Message 47287

While light is additive I don't think that can be used as a blanket statement to justify using an additive blend mode anytime light is involved :) In fact I'm pretty sure that real lens flares aren't additive but a weighted blend very much like the 'normal' blend mode in AE.

UnMult would be the 'correct' way to go but I'll be the first to admit that I'll use 'Add' when I think it looks better!

UnMult is available free (with registration) from Red Giant:

http://www.redgiantsoftware.com/products/all/knoll-unmult-free/

Also as an alternative to UnMult you can apply Shift Channels, set "Take Alpha From" to Luminance and either change the layer's blend mode to Luminescent Premultiply (works in all bpc settings) or apply Remove Color Matting and disable Clip HDR Results (only works in 32bpc). Screen is also a decent approximation in 8 or 16bpc.

On Fri, Jan 4, 2013 at 10:12 AM, Brendan Bolles <brendan@fnordware.com> wrote:

On Jan 4, 2013, at 8:17 AM, Steve Oakley wrote:

> FWIW I have no idea with lens flare filters don't generate their own alpha....
>

Because in nature light is purely additive thing and never covers up the background so much as obscures it by blowing out to white. So keeping the opaque AE layer on top of the comp and using Add or Screen is the proper way to simulate that.

In a compositor that uses premultiplied pixels internally, you could create a layer that had a flare and no alpha, which mathematically results in the same thing as AE's straight-pixel opaque layers set to Add.

The UnMult effect is best for situations where you're rendering out an element for a program doesn't have Add or Screen transfer modes (are there any more like that?). Since the Normal transfer mode involves a multiply by alpha, UnMult creates an alpha and divides by it to try to get the result to come out the same.

Brendan

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