• VEGAS Pro

  Strange Behaviour of Alpha

  Posted by Roger Woolnough on July 21, 2012 at 1:52 pm

  I have been trying to understand compositing in Movie Studio HD Platinum 11. I concluded that applying alpha values on a track should be equivalent to using the “composite level envelope”, which also goes from 0% (zero opacity or transparent) to 1 or 100% (completely opaque or zero transparency).

  The attached video shows four still frames, each one fading twice, firstly using composite level envelope, and then the same still faded using alpha going from 1 to 0.

  Why do the fades done with alpha look wrong compared with the fades done with composite level envelope? Is this a bug in Vegas which we should refer to Sony? If it is intended behaviour, why so? Or, am I not understanding what alpha is supposed to do?

  I tried to attach the video, but I don’t know where it went!

  Mike Kujbida replied 13 years, 10 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Roger Woolnough

  July 21, 2012 at 3:39 pm

  My video showing strange fading behaviour using alpha is here:

  https://reels.creativecow.net/film/alpha-testingwmv
• 

  Mike Kujbida

  July 22, 2012 at 3:52 am

  “I concluded that applying alpha values on a track should be equivalent to using the “composite level envelope”, which also goes from 0% (zero opacity or transparent) to 1 or 100% (completely opaque or zero transparency).”

  You’re wrong because they’re completely different things.
  A “composite level envelope” is the same as overlapping two events so that they fade from one to another.

  Alpha channels are used when you designate a specific colour to be transparent.
  An example of this is the basic text event. Drop it on a track with nothing under it and it looks like white text on a black background. Place an event under it though and the black disappears and you’re left with the only the text.
  Chroma key is another example of an alpha channel, using green or blue as the transparent colour after you define it as such.

  In the examples you gave, the stairstep signal is comprised of a series of steps from black to white. If you were to place an event under it and key (what an alpha channel does) it out, you would see the steps disappear one at a time. You could also use the chroma keyer FX on it and pick a specific shade to key out (i.e make transparent).

  I hope I’ve clarified things for you.
  Doing a google search on “alpha channel” will turn up a lot of definitions and examples.

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