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After Effects - Exporting .Mov with Transparent Layer for Projection in a theatre

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Michael MannionAfter Effects - Exporting .Mov with Transparent Layer for Projection in a theatre
by on Aug 19, 2012 at 6:51:52 pm

Hello folks,

I'm basically trying to export a .Mov with a truly transparant background to used with a projector in a theatre show.

In essence the on stage set will have the background image painted on it and we will be projecting images and video on to that pre painted background.

On the exports we have done we have activated the transparant layer key and also exported out with the alpha channel as well as the RGB one. We get an export that has a black background and we are pretty sure that this would turn up on the stage set and therefore just be a black screen with the animated images on it.

When you drop this .Mov over other video in FCP the black background does disappear, as it should do.

Basically how do I get a truly transparent background on my video??


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Brian CharlesRe: After Effects - Exporting .Mov with Transparent Layer for Projection in a theatre
by on Aug 20, 2012 at 12:34:12 am

Its not possible the way you are thinking. The alpha channel can only be read by a compositing program and does nothing for transparency when projected.

However, this may work for you:

Since the projector would projects black with your current render, why not render with a white background? Then you'd only have white light and no image in that area.



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Matthew WoodsRe: After Effects - Exporting .Mov with Transparent Layer for Projection in a theatre
by on Aug 20, 2012 at 1:42:51 pm

There is no such thing a "transparent" when it comes to projection. The "transparency" of a movie is only useful if you are layering it with something else digitally, like other video or over a web page. The best you can get with projection is what we call "video black". Unfortunately, with projectors its impossible to get full black (complete absence of projected light). Projectors work by putting an LCD in front of a powerful lamp, and even with the lcd on full black, a little light leaks through. Some projectors have a darker video black than others, and if the surface you are projecting on is dark, this video black, can almost disappear, but if its bright you will definitely see a rectangle as your projection area. The only way to avoid this, is to physically mask your projector by putting a metal cutout to block some of the light in front of the projector.

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Walter SoykaRe: After Effects - Exporting .Mov with Transparent Layer for Projection in a theatre
by on Aug 20, 2012 at 3:14:38 pm

As Matthew said, black is the closest you'll get to transparent with projection, because projection works like a very detailed colored light.

Consider projection to work in the real world similarly to how the add or screen blend modes work in After Effects. To that end, you can pre-visualize your project a bit by placing an image of your painted scenic underneath a comp of your animation and setting the animation's blend mode to screen.

Again, as Matthew said, there is no such thing as true video black (although some projectors do get very close!), so you will get a subtle dark gray-looking rectangular wash over your projection area even when projecting full black. (Higher-quality projectors with better [lower] black levels will minimize this; lower-quality projectors with poorer [higher] black levels will accentuate it.) Here are five possible techniques for overcoming this:
  • Always keep an image at the edges as a framing device.
  • Move the imagery in and physically feather the projection cone.
  • Ensure that the projection plane covers your entire visual canvas.
  • Take extra care with additional lighting around the edges of the projection area to minimize their visibility.
  • Use a projection dowser for full blackout moments.


Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
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