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Posted by Bernie on 06/02/06 17:47
"I don't quite get the "alpha" requirement noted earlier. That has
come up before and I was unable to get a clear answer. "
I tried to find a reasonably non-technical description of this from
Google but so far failed, so....
Obviously a picture on a computer disc is just a load of numbers, and
the computer knows from the type of file what to do with it - in this
case display it as a picture. Image files come in numerous varieties -
..bmp. .jpg, .tga etc. Each one has it's different uses and qualities,
and each carries information in addition to the actual visible picture.
Several formats - .png, .tga - allow for an extra invisible picture
layer called an alpha channel which is the same size as the main
picture. Image manipulation programs such as Photoshop let you paint
(or whatever) on the layer. One of the main uses for this is to make
mattes - areas of the main picture to be cut out and made invisible
when the image is combined with video in FCP or whatever.
So if you have a logo/image making program, and Photoshop is the best,
you can design the logo on black, and then tell the alpha channel layer
to be black where the main picture is black, and white everywhere else.
The you save the picture as a targa (.tga) file, and when you put it on
a track in FCP, it automatically cuts out the shape of the logo. If
you have some greys in the alpha channel, you get semi-transparent in
the video.
Given that you want to fade it in and out every so often, I recommend
you put the logo on in FCE after everything else is done, just before
you play it back out to tape.
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