ALPHA CHANNELS?

[Kelley]

I've searched through the manuals looking for info on how to access Alpha Channels, but nobody says much more than it can be done.

 

When I get the tanks going, I want several attack-choppers to sweep in shooting. I want motion blur on the rotors, but not in the whole scene. I figured to turn off everything in the scene, leaving only the turning blades, run the anim., then turn off the rotors, run again, and composite in Premier.

 

But where do I go to get Alpha Channel mode?

[Paul Forwood]

In your render options expand the Buffers folder and set Alpha to ON.

[Kelley]

In your render options expand the Buffers folder and set Alpha to ON.

 

Outstanding! Thanks. I love simple solutions!

[Kelley]

I rendered out two [2 sec.] sequences. I turned off all objects and lights in Properties, and spec'd an Alpha for each. The first, the chopper rotors with much motion blur, and the second is the chopper body. Both sequences rendered out with a solid black background [which I assume is the Alpha Channel.

 

However; I attempted to matt them together in Premier Pro and the top channel [rotors] just shows rotors with solid black. No chopper bawd under it.

 

Is there another step that I'm missing? I recall from school [10 yrs. ago now] working with an early version of Premier and there was a way to choose a color and set it 'Transparent'. Is something like this necessary?

 

Thanks

[heyvern]

I think the step missing is probably in Premier. You need to specify that that the alpha in the file should be used. I am guessing since my version or Premier is many years old but I seem to recall that the alpha had to be "intentionally" set.

 

I know in my older version of After Effects how to handle the extra channel was "asked" when importing with several options for premultiply, not premultiply, ignore or whatever.

 

-vern

[Kelley]

I think the step missing is probably in Premier.

 

And so it was. I was surprised that the index only had two or three entries for Alpha Channel. A light treatment for something so central to Premier. One of the entries is 'Alpha Adjust Key'. Something that rang no bells, hence it couldn't be...

 

But it was. Barely half a page. But the key tells Premier that an Alpha is present. Tomorrow morning I'll run another test.

 

Thanks much!

[robcat2075]

Both sequences rendered out with a solid black background [which I assume is the Alpha Channel.

 

Actually, the black is what the alpha channel is allowing to appear in those areas... nothing. If you want to see the alpha channel load a frame as a targa into Photoshop and look at the channels.

[Kelley]

Both sequences rendered out with a solid black background [which I assume is the Alpha Channel.

 

Actually, the black is what the alpha channel is allowing to appear in those areas... nothing. If you want to see the alpha channel load a frame as a targa into Photoshop and look at the channels.

 

Great! Thanks Robcat. I was just chewing on the Alpha problem as I went back to the Premier project and tried tp follow the advice tendered above. The book says click on a film clip in the Project window, go File>Interpret footage and you'll get a dialog box...but I find 'Intrepret Footage' greyed out. This will allow me to double check that the Alpha is there.

 

A footnote to the foregoing: I took a .tga still [w/ an Alpha Channel made in Photoshop] into the Premier project and overlayed it onto a 2 sec, spinning rotor .avi clip. The "Interpret Footage" showed up, I rendered it out, and the Number 22 was nicely layered over the rotors.

 

Writing this, I'm wondering if I should render my A:M videos as .tga?

 

Targa. Of course. Wuz allwis a little slower then th rest of the children.

[Xtaz]

Hi Robert .. I dont know if I understood correctly ... are you trying to simulate spinning props ???if it's the problem I advice you to know MUFOOF ..

[KenH]

I'm trying to find the alpha channel option myself but it's not where it used to be. Does it depend on the avi type?

[Xtaz]

Hi Ken ... AVI doesnt support alpha channel ... you must use MOV format to enable it..

[John Bigboote]

I thought AVI supported alpha...could be the type of compression specified that disallows an alpha...kinda like using 'ANIMATION' compression as opposed to "SORENSON3' in the quicktime realm- meaning ANIMATION will support alpha and Sorenson3 won't. I think AVI with NO compression will support an alpha channel.

[Kelley]

Hi Robert .. I dont know if I understood correctly ... are you trying to simulate spinning props ???if it's the problem I advice you to know MUFOOF ..

 

Right. Right. That is what I'm shooting for. And thanks for jogging the memory. I recall seeing a run-down on that once upon a day and thinking to myself 'this could be valuable'. Howe're, I recall it being discussed for rendering a still as though it were from a video. But I will definitely check this out.

 

ps: just found the link...and it was your posting. Cool. I had forgotten how much good stuff was in it. I can see some practice ahead with flame. Thanks.