Alpha Channel output without affecting the image?

[Chris Smith]

Set it to straight alpha instead of premultiplied alpha when you render out.

Chris Smith
https://www.sugarfilmproduction.com

[Special Needs]

Thanks. I tried that and I got just the alpha channel. I need the the full (non-blacked out) RGB and the animated alpha channel in one file so that I can send it to someone who will work with it in FCP. OR is there a way to take that straight alpha channel and add it to a clip in FCP? I tried using the Image Mask filter but it only uses the first frame as a static mask. I’m stumped.

Thanks!

Sean

[Jeff Dobrow]

I think Chris meant:

Set it to rgb+alpha, AND then set alpha to pre-multiplied. (it will look like crap until it is placed in an NLE or Comp. app)….

[Special Needs]

Jeff,

Thanks but still no luck. I’m guessing that I’m missing something simple. Here’s my work:

Import Quicktime clip into AE
Place it in composition
Add Mask to the layer I just ceated
Animate mask manually (This blacks out what is outside the mask unless I set the mask blening mode to None – in which case I get an alpha channel that fills the screen – rather than where my mask is)
Add to render cue
In Custom output – RGB+Alpha, Straight (have also tried Pre-Mulit)

Do I add a copy of the clip underneath and somehow turn off it’s ability at affect the alpha channel? No matter what I try, I either get a solid alpha channel with the full clip or a blacked out clip with the correct masked alpha channel. I’ve been over the manual and many sites but I can’t seem to find the key.

Thanks!

[Bobby Walker ii]

I think your problem may be with your FCP operator. Next time he imports the movie have him double click the movie then go under the modify menu and check that the alpha channel is set to straight. The setting may be set to black which will give you the fringin.

A second thought…

You don’t say what codec your rendering to. The only ones with alpha channel that I can think of immediately are Animation and Microcosm. You should be rendering to one of these….

hth-

bobby walker ii
broadcast video COW

G5 2.5GHZ DP,2.5 RAM, AJA IO LA, Medea G-Raid,FCP HD

[Special Needs]

No, the files come into FCP as straight – I’m testing it here. I’m sorry to be such a pest. No matter what I do, if it’s masked in AE, the main RGB frame is blacked out in the rendered file. I need to find a way to render it and have the final output mask only show in the alpha channel – so if you didn’t look at the alpha channel, you wouldn’t know it was there.

Thanks!

[Jeff Dobrow]

hmmm….

1) When you are in your timeline with this setup, and click the ‘alpha only’ disply option on the viewport,…do you see the correct alpha?? If yes then go on, if not…you have something setup wrong.

2) If you do,….then render it out. Bring it back into AE, and see if it has the correct alpha?

3) If it DOES then its a FCP issue,…if not then hmmmm….you are animating a shape on a layer above your fill layer and using it as a track matte?….Is that correct?

[Jeff Dobrow]

OH,..ok….you are simply using a bezier type mask on a QT with NO other layers in scene. Then you are rendering to a fileformat that supports alpha with a proper codec. RGB+alpha, straight…and it is not working?….SOunds like a codec/file format issue. It has to be,…as what you are trying to do should be so blindingly simple.

Try it on a solid…no QT,….render a frame or 2 as a 32-bit .tga with rgb+alpha/straight. Bring back into AE,…drop in timeline, see how it looks (remember to interpret as straight alpha). If it works then I would suspect the codec/fileformat setup or configuration.