Re: [Avid-L2] To break the cone of silence when did Avid add premultiplied Foreground into Matte Key?

So the premultiplied is what the GVG would classify as "Shaped".  I've heard it described as the fill output of the key source is pre-keyed over whatever the background of the device is set to.  In Avid, and I haven't tried this in a while, with title tool if you make a regular title the fill or foreground is shaped but if you tell it to have a soft shadow then the foreground will be unshaped and have all kinds of funky spill over at the edges of the key objects.

Now I was always told to ask for straight keys from After Effects not premultiplied am I still correct in that?


On Thu, Apr 9, 2020 at 11:04 PM, bouke wrote:

On 10 Apr 2020, at 06:33, John Moore <bigfish@pacbell.net> wrote:

regular key and linear key that allowed for a feathered key.  I've always considered premultiplied vs. straight in the same way 

Big mistake. The alpha is always ‘feathered’ (A bw gradient defining the opacity.)

 

The difference is in the foreground. A straight alpha file has all colors ‘as they are’ before applying the key. Hence they can look very strange if you have heavy gradients (fade to opaque.)

Premultiplied has the fg mixed to black based on the alpha, so if you open a file without applying the key it looks pretty, same as a non straight keyed to black.

 

Mathematical there is no difference between the two, but indeed the keying app (in this case Avid) must be able to undo the math, and hence it must know what to expect.

 

Bouke

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