Blackmagic Forum

hello guys.

I have a clip with an alpha channel and I want to use the "camera shake" effect.
But the big problem is, (I think it is because of the random seed) that the alpha channel is shaking differently than the video....

I want to keep the alpha channel - so compound clip is not working.

Is there a solution?

Mmmmm...alpha is just a "see thorough" portion of the frame. Soooo, I'm confused about how you're 'seeing' it move?

Jim Simon wrote:Mmmmm...alpha is just a "see thorough" portion of the frame. Soooo, I'm confused about how you're 'seeing' it move?

Take a piece of paper, cut a hole into it and wiggle around. You can’t see paper that isn’t there yet I believe you can still see the hole move...

Ahh. You have the alpha inside the image. I was thinking of it outside the image, as if the circle you cut out is the image, and the rest of the paper you threw away is the alpha.

Jim Simon wrote:Ahh. You have the alpha inside the image. I was thinking of it outside the image, as if the circle you cut out is the image, and the rest of the paper you threw away is the alpha.

It makes no difference, you see it in both cases. Mismatch of alpha is like bad roto that wobbles.

You have to wire in the upstream alpha into the OFX camera shake node, Right-click the camera shake node, and select "Use OFX alpha" from the dropdown, then add an alpha output to your node tree, wire that up, and violà. Works in R17b8, not sure about earlier. I know OFX alpha clamping was a recent fix in the release notes. If the motion blur wasn't clamped accurately, it might appear to be a little off, temporally.

Hendrik Proosa wrote:you see it in both cases.

That doesn't make sense.

If the circle is the image, and the paper around that which you discarded is the alpha, then there's nothing around that image for you to see. So how can you 'see' that nothing move differently?

What am I missing here?

Jim Simon wrote:

Hendrik Proosa wrote:you see it in both cases.

That doesn't make sense.

If the circle is the image, and the paper around that which you discarded is the alpha, then there's nothing around that image for you to see. So how can you 'see' that nothing move differently?

What am I missing here?

I don’t know what you are missing, it is all very simple. Do a bad roto, invert the matte and see if wobble magically disappears or not.

Jason Conrad wrote:You have to wire in the upstream alpha into the OFX camera shake node, Right-click the camera shake node, and select "Use OFX alpha" from the dropdown, then add an alpha output to your node tree, wire that up, and violà. Works in R17b8, not sure about earlier. I know OFX alpha clamping was a recent fix in the release notes. If the motion blur wasn't clamped accurately, it might appear to be a little off, temporally.

Screen Shot 2021-02-05 at 2444.jpg

OOOH, thank you!