Premiere Pro 2.0 and problem with difference matte...

[arminio]

I primarily want to blur background and keep foreground sharp (looks like videos made with short focus lenses has) - I thought to do that using difference matte because I shoot my clip with camera fixed on tripod and with static background (which need to be blurred) and moving foregrond (need to stay sharp).
But looks like this filter is buggy... Whatever I do I can't get it propperly working! I made image of static background and used difference matte but it keeps give me incorrect transparent regions!
Any idea how to achieve simmilar result using some other keying techniques?

[Guiboche]

The Difference Matte effect is not what you want to use to create this effect. But it's sorta in the right direction.

In order to create this effect, you need to use the Compound Blur with a Black/White source ( see this thread: https://forum.videohelp.com/viewtopic.php?t=319142&highlight= )

What you need is a matte for that foreground object. Unfortunately, it might not be easy to create that. You can either roto the foreground object. Or, try and use the Difference Matte filter to generate a matte.

The Difference Matte will create a black/white source (alpha channel) based the movement in the image. A static background will become black (transparent), and whatever is moving will become white (opaque).

Good luck!

[arminio]

>The Difference Matte will create a black/white source (alpha channel) based the movement in the
> image. A static background will become black (transparent), and whatever is moving will
>become white (opaque).

Yes. That's what I have in mind - to create mask based on static part of picture using difference mate but that filter doesn't work correctly!
I found workaround on Internet but I don't understand how to apply it because it is written in a form of "equation":

((Invert + Opaque 50%) + Key Image) * RGB Difference (Gray) = Difference Matte Key withgout bugs and stuff.

Any ideas how to "parse" this?

[Guiboche]

I don't understand how to parse that, but I've only ever used the Difference Matte inside After Effects. Never had a problem with it.

I'm assuming it would work the same in Premiere, but I could be wrong....