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Posted by Gene E. Bloch on 06/02/06 19:05
On 6/02/2006, Bernie posted this:
> "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.
Thanks for the explanation - I never knew either, and what you wrote is
very clear. It will help the OP as well :-)
--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")
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