Compositing Challenge

Question

Hello. My son and I are going to shoot a promo for his website. He's a 9th grader, and I'm a single Dad, so we're trying to do this on the cheap. I'm wondering if folks out there can give advice about how we might be able to use After Effects to solve a problem. In this video, we will be crushing an iPad that is playing an animation. Well, we won’t actually be crushing a working iPad. I have the glass front and the aluminum back panel. No board. No LCD panel. So, the glass is clear, which is perfect. To make this work, I’m going to put a green screen inside the glass of the partial iPad and, in After Effects, replace the green screen with the animation. This way, when we crush the iPad, it will look like we’re crushing a working iPad with the animation running on it. The crush will be so quick that we can, in post, remove the green screened image. If anything, it will look like the screen went blank as the foot hit it. That’s fine. The problem I’m having, however, is that when crushing under foot an iPad with a green screen inside of it, the green fabric (or paper) will be seen clearly in the pile of broken iPad scraps left on the ground. Do you follow so far? Do you understand the problem?
I’m writing to you for your advice on how to solve this.
Options I’ve come up with so far:
Put a green plastic film inside of the clear screen. When the foot touches the top of the iPad (it will be in a stand so it is vertical), the image of the animation is turned off. Problem with this approach:When the animation is removed from the green screen, we’ll be left with a green screen as the foot comes down. We’ll also see the green plastic on the ground in the pile of mess that was the former iPad. Question:  if we use a green film, can we replace the green with black in post-production so that the screen looks black when the animation is removed and, also, so that the sheet, when lying on the ground, looks black, which the viewer would interpret as being merely the black insides of an iPad (the LCD film, perhaps?)?
In After Effects, add a color layer and shape it to fit over the clear glass screen. The color would be green, and that layer would then serve as the green screen we’d composite out and replace with the animation. When the foot touches the top of the iPad, we could turn off the compositing (which would remove the animation) and replace the green with black. We could then artifically shatter that layer as the foot progresses through the stomp. Problem with this approach:I don’t know if you can create an artificial green screen in After Effects using layers. Do you think this could be done?
Find a way to affix green powder or paint to the insdide of the clear glass iPad screen. Then, turn off the composited animation as the foot stomps and replace it with black as the glass shatters.Problems with this approach:I think we’d wind up with either green shards (if we can’t carry the compositing through after the glass has shattered) or black glass shards if we can carry it through. Black would be acceptable. Green wouldn’t. I wonder if we could replace green with “clear?”
Any advice you could offer would be really appreciated by a kid trying to make a hit. :-)
Thanks.
Glenn

Answer 1

theglennotf wrote:
No need for compositing. Am I on the right track here?
Sorry, no.  You face a good deal of work.  Compositing means much more than simply pulling a chroma key.
You'll have to be careful when you shoot to get a "clean plate" of the unaffected prop.  Just to have it.  You may not even use it, but it's there in a pinch.  You'll end up using the same shot in many different way, and on many different layers in AE.
You'll create an animated mask around the foot: the rotoscoping part.
You'll use Mocha to cut the hole for the screen, behind which you'll put the new display.
You'll use the Mocha Layer again to display the screen only, so that you can use its reflections and its general look to make the new display look more realistic.
Since this device will doubtlessly move as the foot steps on it, you'll have to move the display layer accordingly, either via motion tracking supplied by Mocha, using AE's built-in Motion tracking, or animating the display's position by hand.
So while there's no green-screening, you can see it takes a lot to pull off a realistic-looking shot.
I should also mention that if you're an AE novice, this isn't the type of work novices are equipped to undertake.  AE really does require a firm grounding in the basics before moving to the fun stuff.  Sidestepping the basics almost always results in wasted time, wasted effort and frustration.
Here's a good place to begin learning the basics, and it's all free:
http://blogs.adobe.com/toddkopriva/2010/01/getting-started-with-after-eff.html