How do I retain my alpha channel?

[THX1138]

Hi guys.

I'm no After Effects expert. In fact, quite the opposite (i.e., After Effects retard).
I created a simple title animation in Apple's LiveType which was then exported with an alpha channel.
When I bring this QT file into AE, it says the file has an unlabeled alpha channel and prompts me to make a selection. I chose "guess" as I was informed AE will make a beep sound if it cannot guess correctly.
I added Shine effects in AE and then exported, but no alpha channel. The background is black, so I cannot layer it over a picture in my video.
I can't seem to figure out what I'm doing wrong.

Suggestions?

Thanks.
travis

[graymachine]

If there is indeed an Alpha channel, when you import the file, select Premultiplied with black as the color.

If you still don't see one, then there is no alpha channel.

[craigbowman]

When you are setting up the Render queue, in the output module dialog box under the Video Output section, go to the channels output popup menu and choose "RGB + Alpha".

That's it.

[THX1138]

craigbowman,

Am I only able to set the Render queue when I first create the comp? I want to take the one I currently have and change the settings to match what you said, without having to build a whole new project.


Graymachine,

When I chose "guess" AE set it to what you describe. I can tell you that the .mov from LT did have an Alpha channel, as I tested in FCP. The one from AE, using that same file, did not.

[Sacksnack]

Render Que setting can be adjusted at any time and have nothing to do with the comp settings. Just as craigbowman said, after you've applied your shine, and you're ready to render out your final piece, under "Output Module," you can go into custom settings and select "RGB+Alpha" under channels.

Hope this helps
-Kevin

[Matt Grunau]

Unless you specifically set an alpha channel to be premultiplied (as in to be put against a black or white background, and yes, that's all), interperate as straight. If it's comping from any regular app that supposts alpha channels, it's going to be straight, unless you pretty much tell your original app to make it premultiplied (something you should never do anyway, as it serves no purpose).

[graymachine]

Premultiplication serves no purpose?

AE's default output is premultiplied.

Just about every image sequence I've received from any 3D app or animator has needed premultiplication to eliminate halos and blamming. Very rarely do I ever see straight alphas come my way... in fact, the only artists I routinely receive straight alpha images from are Flame operators.

This page seems to do a fairly decent job as explaining it:

http://www.damonledet.com/tutorial/index.cfm/name/Alpha_Channels

[Matt Grunau]

Premultiplication serves no purpose?

AE's default output is premultiplied.

Just about every image sequence I've received from any 3D app or animator has needed premultiplication to eliminate halos and blamming. Very rarely do I ever see straight alphas come my way... in fact, the only artists I routinely receive straight alpha images from are Flame operators.



AE's default Alphas are Straight, for evertyhing I have ever used them for and that includes all elements I have rendered to be used back in AE. All the other renders I have done (from Lightwave mostly, but from other progs as well) are always straight as well.

The reason you need to use premult to eliminate halos and such is because they were encoded wrongly to begin with.


Mark Christiansen After Effects Studio Techniques:

"Premultiplication exists for one reason only: so that source images look nice, with realistic, anti-aliased edges, before they've been composited.

That's right, we have premultiplication just so that a matted object looks right against a black background when is comes out of, say, your 3D animation program. All premuliplication does is composite the footage against the background, so that the edges and transparency blend as well into that solid color (typically black) as they would against the final background."

So unless you final destination is a solid, Premultiplying alphas is unnecsarry and wrong.

[nessworks]

I created a small spinning globe in AE. In my render queue, I used Alpha+RGB in AE 7.0, Render Video File. Then I would like to import the Video into Vegas. I am using Vegas 6.0. I tried all of the composition settings in the Upper Vegas Video track, but my small globe has a black background in Vegas and always seems to be transparent? Is there a setting I am missing in AE or Vegas???.
I have always put non animated graphics on a Transparent Background in Photoshop and imported them into Vegas. But I would like to create "Motion Graphics" in AE and then import the video file into Vegas.

Any help is appreciated.

Note: I used a black background in the composition. I can import a section of video and do it in AE, but I would like to learn how to create in AE and import into Vegas, just like you see the logos on Tv all the time ...

[craigbowman]

I created a small spinning globe in AE. In my render queue, I used Alpha+RGB in AE 7.0, ...

RGB+Alpha doesn't create an Alpha channel. It allows an existing Alpha channel to be included with the output. If you want your globe to have an alpha then you must create a mask around it or generate a key from the background first.

[nessworks]

Thanks for your response Craig. I dove into After Effects at the beginning of the summer because I wanted to increase my skills in Motion Graphics. Example Text fly ins, Spinning Globes, etc ... I am doing OK in AE ... only getting back into the NLE "transparent" is my struggle, like THX1138 addresses. So I am a bit confused on the process in AE or the final render procedure with the goal of of using the AE project over video in my editor.
Sorry for the Newbie question ...

[Neil Rowe]

..yep. its all been said, but i would import and interpret as striaght alpha since it wasnt something shot against black.. it was generated with a transparent background. then use some codec that allows for an alpha channel on export/render que like planar RGB using millions of colors +.. or jpg2000 or whatever you want to use for a codec that supports and alpha channel(will show millions of colors+ as option in color depth.. the + indicates that its also outputting an alpha channel. then just export. anything with an alpha value in the comp will be exported with that same alpha .. just be sure you set up a transparent background in the comp, and didnt make a solid colored one, otherwise the colored background will get composited into the scene, and your not going to get the transparent background your looking for. its generally easy to set up a colored solid to use as you background so that you can see clearly where composited items are in the scene, and then just turn off visibility for the solid layer before rendering.

[nessworks]

That's what I was missing! Setting up a transparent background in the comp!
I had it on top of a black background. I will set up a new transparent background in the comp and use the black background during design and make sure I turn off the visibility of the black background before render.

Thanks Neil, Thanks All.

[nessworks]

I cannot figure out how to make a background layer Transparent in the Comp! Looking on-line for a tutorial and in the AE help files ... I still can't get it?
I saw this tutorial on line: I see this is possible ...
http://video.nessworks.com/images/aecomp1.jpg

This is what mine looks like:
http://video.nessworks.com/images/aecomp2.jpg

Quick Tip? Keystrokes?

[Sacksnack]

The button just left of "active camera" will toggle the transparency. But it's just a visual aid. You can leave your comp black and you'll still have the alpha channel.

[nessworks]

Thanks for that tip Sacksnack. Man ... I can't believe I missed that! I am still struggling rendering to a transparent background.
Like Neil mentioined, turn off the visibility of the background track before rendering.
How do I do that?

Here is the URL to a screen shot of my current project.
http://video.nessworks.com/images/AE_Render1.gif

When I set up the Comp, I used a green background ... Can I set this to transparent? When I render down ... just like Neil mentions, the background gets rendered in with the final. Do I need to create a seperate adjustment layer in the comp at the beginning of the project?

Here is a link to download a zip file of the real basic motion project if anyone would like to view and advise me on how to turn off the background so when I render it I can overlay in a NLE. Thank You.

http://video.nessworks.com/zip/AE_STAFF.zip

[dougspice]

The solid background WILL get rendered as visual information, but if you're able to tell Vegas to interpret your alpha, it'll go away. I don't know anything about Vegas.

As a test, try reimporting your rendered file into AE and look at it there. What's in the the alpha channel?

[chud13]

This has been answered already, but I will try to put it different terms. If you have a solid as the background and you render it lossless with alpha, you will still see the background after you render it. If you delete your solid as the background and are just seeing the background color for the comp and then you render it lossless with alpha, you won't render the background.
So, yellow solid as background + render lossless w/alpha = yellow background.
No solid and background color set as yellow + lossless w/alpha = transparent background (at least when you import that movie back into after effects.)
As for turning off solid layer, there is an eyeball on that layer. Click it. If there is no eyeball, trying clicking on the switches/modes at the bottom of the timeline.