2 Replies Latest reply on Aug 5, 2009 7:29 AM by Applied CD

    Compositing order for alpha channels?

    Applied CD Level 1

      I’ve got a movie clip of the earth with a shadow mask that moves to simulate sunrise from space. This clip is placed on the main timeline where it is tweened from alpha 0 to alpha 100. My problem is that the main timeline tweening is applied to the shadow and earth independently, ruining my moving shadow effect. Is there a way to get Flash to composite elements in the movie clip first, then apply the alpha tweening from the main timeline to the composite movie clip, not to the individual elements that make up the clip. Here’s a link to the work in progress: http://www.appliedcd.com/cap/eltMission.html

        • 1. Re: Compositing order for alpha channels?
          robdillon Most Valuable Participant

          I think that this is a perception problem, not a mechanical one. You have to density effects happening at the same time. You are increasing the alpha of the earth/shadow clip while moving the shadow in the clip which changes the density of the earth. So while you are increasing the amount of the earth that is seen by moving the shadow, you are also increasing the alpha of that same earth. All of this is coming up out of a black background. The net result is an increasing crescent of the earth appearing.

           

          Have you tried the animation without the alpha change? Just move the shadow to gradually expose the earth? Or show a very slim crescent of the earth as the alpha increases and then animate the shadow?

          1 person found this helpful
          • 2. Re: Compositing order for alpha channels?
            Applied CD Level 1

            Hey Rob,

             

            Thanks for looking. Yeah, I’ve tried removing the main timeline alpha tween and the globe (even though mostly black) becomes too prominent during the early part of the transition. There’s some interesting compositing between the ATC radar screen and the globe during the transition that gets lost as well. If I have to compromise, so far I’d rather lose the shadow effect.

             

            I’m not so sure the problem is perceptual however. If you were to pick a point on the earth still in full shadow when the clip density on the main timeline is 25%, what I want for that point is:

             

            (100% shadow over 100% earth = 100% shadow) x 25% clip density = 25% shadow over star field (the background in the main timeline)

             

            What Flash does instead is apply the clip density to the individual elements first:

             

            (100% shadow x 25% clip density = 25% shadow) over (100% earth x 25% clip density = 25% earth) over star field, allowing the globe to show where it should be just shadow over stars.

             

            I’m gonna fiddle with this a little more. There are other aspects of the transition I’m not happy with (too many frames, slows down pacing (I’m hoping music still to come will help) and some performance issues on slower machines (the radar zoom, the globe, shadow mask, and star fields are huge, moving, and have density filters applied causing the transition to “chug” on some machines - sometimes I wish I still had Director's speed for pushing pixels ;-))

             

            - Bob