Alpha channel AE cs3?

[Topher Welsh]

[Hamid Rohi-Bilverdy] “I tried a couple of times now, but i only get a black screen in the back :-(“

Your footage does have the background transparent, just by default you screen has a black background. There is a switch at the bottom of you preview window that has a white/grey checkerboard, hit that, and you should see that the background is transparent.

Or you could just find a background jpeg and drag it into your comp underneath your footage so your layers would look like this:

FOOTAGE
BACKGROUND_Picture.jpg

Topher Welsh
Head Editor & Motion Graphics
http://www.scout.com

[Nel Johnson]

Hey Hamid – Topher is correct on this.

I’d also add that it’s unclear from your post how you are importing and using the video in Flash.

Creating video with transparency requires a certain type of render out of AE, typically a codec which allows for RGB plus Alpha or ‘Millions+’. A lossless codec such as ‘Animation’ would give you this (although I’m not sure how Flash would handle a file like this). High compression codecs such generally throw away the alpha channel to save on filesize.

You could also render out to an image sequence of a type that supports transparency, maybe PNG or Photoshop.

Hope this helps.

[Hamid Rohi-bilverdy]

Hi Topher..

Thanks for quick reply 🙂

Ok, before trying with the picture underneath the footage, I would like to try your first approch..

Where exactly is the

“switch at the bottom of the preview window that has a white/grey checkerboard, hit that”

You mean in aftereffect right? Cant find it..

Regards Hamid

[Hamid Rohi-bilverdy]

Hi nel johnson ..

Well i want to import it to flash after i it have bin trough the flash video encoder.

Regarding my first approch, i followed the book and in there i also tried

“Creating video with transparency requires a certain type of render out of AE, typically a codec which allows for RGB plus Alpha or ‘Millions+’. A lossless codec such as ‘Animation”

After this i got the black screen. But in AE the transperacy looks great.

I know it´s probraly just me, so if you could guide me trough make this happend, would be much appreciated. I really need this.

Regards Hamid

[Topher Welsh]

Here is a picture of where the transparency switch is.

https://img169.imageshack.us/img169/2046/tswitchqu9.jpg

once you click that off, your default background will be gone, and then you can stick a picture or more footage behind your keyed out footage.

I think what you are trying to do with the whole flash video idea is you just want to make it a flash video once you have a finished product.

I would just focus mainly on creating the keyed out footage the way that you want it in After Effects, and then export that to a file such as quicktime or .avi and then find a free converter somewhere like download.com

Unless AE has a flash export setting that I can’t find for the life of me.

Topher Welsh
Head Editor & Motion Graphics
http://www.scout.com

[Nel Johnson]

Hi Hamid,

You’ll have to forgive my ignorance of Flash and whether certain types of video will import. Can you give me some more info as to what you are hoping to achieve in Flash. What background are you aiming to view through the transparency?

The reason I ask is that I’m trying to work out why you are using Flash to do what After Effects is actually built to do, ie. compositing.

nel.

[Hamid Rohi-bilverdy]

Okay guys..

Yes topher, i allready checked the toggle grid for transperacy on. Thats working fine. But when i export the movie as a mov, avi or mpeg, ot all come out the same. I still cant see trough it. Black screen.

Nel: ofcourse, i should have started out with saying what im hoping to achieve. I have recorded my self on a green screen, and i wanna use the video as a web host on my site. The reason for it to be transparent is that im gonna have text and graphic behind it, also if i change the colors a lot in the main flash movie background, it is good to have a transparent movieclip I even may use it on a big PNG..

I hope this made any sence, or please write me back..

Regards Hamid

[Topher Welsh]

Check your render settings and make sure in the VIDEO OUTPUT that CHANNELS are set to RGB+Alpha

Topher Welsh
Head Editor & Motion Graphics
http://www.scout.com

[Erik Pontius]

Also keep in mind that if you are looking at the file in Quicktime, you will see a black background, since QT is not using the alpha channel. If you import the rendered file back in to AE, the background should disappear since AE will use the alpha channel to remove the background. Also, remember that AE can create two different types of alpha channels. Straight and Pre-multiplied. The default is Pre-multiplied, which includes your comp background color. Straight is preferable and cleaner in most cases, but looks pretty horrible if you just look at it in QT, since it does not include the background color.

Also if you are exporting to flash FLV, to then import into a Flash project, you will want to make sure that you are using at least a Flash 8 encoder and turn on the option for transparency. Otherwise, the flash encoder will discard the alpha channel (versions earlier than 8 didn’t have support for alphas).
You only need to do render flash with alpha if you intend on keeping the alpha channel so that your imported video sits seamlessly over a background that is in your Flash project.

Erik

[Hamid Rohi-bilverdy]

Allright you guys!!! It worked out… I just followed the steps from the book again, and tried to see what i missed.

In the beginning before i pack my clip down to the timline area, i forgot to right click on my file and choose “interpret footage” and the click on main.

Anyways, so i got it transparent now, and it worked fine when i imported it to flash project. But why cant i see my background text, grapics or something like that?

It´s like it is only transparent after the background color??
‘
Please advice

Reagards Hamid