I've been considering purchasing some of Footage Firm's Alpha Channel Effects DVD's. However, I notice that most of the ones I'm considering are of fire, smoke, and the like. These images come on DVD and are super-imposed on a clear background (obviously); but... smoke and fire vary in intensity. I was under the impression that Alpha channels were either solid or transparent, not 'partially' transparent (eg. as smoke thins, it is translucent... not a solid color, and not completely clear). If I drop a smoke effect on top of another video clip, will the underlying video clip show (partially) through the smoke (with a kind of hazy, translucency)? I'm thinking 'No', but I haven't done much with Alpha channels before. Anyone have any info about this?
Thanks very much!
typically an alpha channel could have shades of transparency... an 8-bit alpha channel (typical of many file types) could have 256 shades or transparency. formats that support higher bit depths have more levels of transparency.
an animated gif, however, is just a 1-bit alpha (transparent or opaque) and that may be what you are thinking of.
now, i can't attest to how the footage you looking at is keyed, however, if you can view just the alpha channel (or matte) for the footage, then you could tell for sure how much transparency there would be. the alpha/matte would look like a black and white clip, with darker areas being more transparent and lighter areas more opaque.
[Vic Noseworthy]"...I was under the impression that Alpha channels were either solid or transparent..."
Good news! You can forget that impression! Alpha Channels can indeed have varying degrees of opacity & transparency. You may purchase those stock footage clips confident in knowing they will perform as advertised.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA