13 Replies Latest reply on Nov 15, 2011 4:18 PM by bogiesan

    Compositing Challenge


      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:


      1. 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.
        1. Problem with this approach:
          1. 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.
            1. 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?)?
      2. 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.
        1. Problem with this approach:
          1. I don’t know if you can create an artificial green screen in After Effects using layers. Do you think this could be done?
      3. 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.
        1. Problems with this approach:
          1. 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. :-)





        • 1. Re: Compositing Challenge
          Dave LaRonde Level 6

          That's a nicely thought-out query.  My congratulations to you. 

          And here's an answer you may have not expected: I don't know if you even NEED a green screen for this trick!


          If you run AE CS 5 or newer, you have access to two good tools, Mocha and Rotobrush.  If the shot has camera movement in it, Mocha will let you track and isolate the device's screen.  You can then insert a new layer while also duplicating the screen layer to use a blend mode, making the display look more realistic.  Since the device is sure to move as it's crushed, this would be a good thing to use.


          Rotobrush will let you isolate the foot on its own layer, which you can then place on top of the screen display layers.

          • 2. Re: Compositing Challenge
            theglennotf Level 1

            Thanks, Dave. You had my heart racing with possibility!


            Sadly, CS4. :-(

            • 3. Re: Compositing Challenge
              Dave LaRonde Level 6

              Well, you still have Mocha-- a very good thing -- and in the absence of Rotobrush, you can use Rotoscoping, which will also work to isolate the foot.  It'll take longer to create the effect, but it can be done.


              Here's a valuable link:

              http://help.adobe.com/en_US/aftereffects/cs/using/WS39e706a46ad531be1172e0812179ce5d44-800 0.html


              You can find it again by going to AE's online Help, and using the search term Rotoscoping.


              The reason why I mention NOT using green screen is because you're doing this on the cheap.  That implies a consumer-grade video camera.  For a variety of technical reasons, they're notoriously poor at precisely recording color information.  And what do you need for a great-looking color key?  Precise color information.

              • 4. Re: Compositing Challenge
                theglennotf Level 1

                Wow, OK. I'm still on the "happy" side of this issue, then. Thanks.


                Dave, when you say "isolate the foot" with Rotoscoping, I (as you can tell) probably don't know enough to understand what you mean. Certainly after spending time with the tutorials, I'll have a better sense of it. Meantime, though, for clarification, I'm wondering if I might actually need to do anything at all with the foot that's stomping the iPad. There's no camera movement. It will be a static shot (done with a consumer-grade camera, yes). The iPad will be stationary in its stand. Your responses have gotten me thinking (as in "duh"). I don't need a green screen, do I? Even in just straight up After Effects, I can place a layer with the animation running over the exact location of the "glass only" iPad, right? Given that the iPad will be small already as it's about eight feet away from the camera, this effect should be easy to do and to do well. I'm right on this, yes? If I am, it's because your reply got me to understand it better.




                I think this problem might now be solved, with this additon. Can you confirm? If it's right, then we're finished here!


                So, I add the layer and fit it to the the "glass-only" iPad frame, covering it completely so it looks like the animation is playing on it. Then, the foot comes down and stomps the screen, at which point, I replace the animation layer with a black layer that looks like the animation has just flashed off (due to the downward striking force of the foot). I can then remove that black layer in an instant. Or, I can spray paint the glass black, and when it shatters, just let the viewer imagine that ipad glass is really black. Not a big deal. Anyway....


                No need for compositing. Am I on the right track here?

                • 5. Re: Compositing Challenge
                  Mylenium Most Valuable Participant

                  The general approach to such matters is not to use any real glass, but do it in a 3D program. That being said, you may have some luck by matchmoving the Shatter effect and using multiple instances of the result as a displacment map, for the edge highlights of the fragments and all that. It's an illusion, after, all. Similarly, with something as rigid as a pad and those things having a special kind of glass, you probably won't be seeing much splintering at all, but only see the spiderweb fractures or the other way around it just crumbles to a collection of very small and harmless, sand-like pieces. Both effects can easily be faked by tracking an animated pre-comp onto the pad or using generic particle systems. Really depends, but in any case you should focus your energy on otehr things than trying to do this with green screening...



                  1 person found this helpful
                  • 6. Re: Compositing Challenge
                    theglennotf Level 1

                    Thanks, Mylenium. I'm going for a real shatter, though. I have a real back, which I'm scoring so it will bend and crush easily. I'll be putting a piece of a circuit board inside, and using the real front glass which isn't, it turns out, so very thick. iPads seem very resitant to damage when fully assembled. In this form, they seem rather fragile indeed.

                    • 7. Re: Compositing Challenge
                      Dave LaRonde Level 6

                      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:



                      • 8. Re: Compositing Challenge
                        theglennotf Level 1

                        Thanks, Dave. I remain confused, however.


                        If all I'm going to do is use AE layers to place the layer of the animation temporarily over the layer of the black spray painted glass, then isn't all I'm really doing is just keeping that animation playing for a few seconds on a completely static iPad front until the foot makes contact with it, at which point, I kill the layer (because the foot will kill the display) and let the blackened glass shatter naturally under foot? I mean, this whole thing is going to be seen from no closer than 8 feet away, so I'm thinking reflections aren't needed, and the millisecond difference between when a footstomp would really kill a display and when this one will be killed (at first contact) will be so very insignificant as to be perceived only by those who are really thinking the whole thing through.


                        I'm most definitely not intending to be argumentative (particularly given that you're offering really awesome tips). I'm really just wondering if I'm missing something or if this is the difference between doing something right for, say, mass commercial consumption, versus doing something that will be totally passable as a YouTube video.

                        • 9. Re: Compositing Challenge
                          Dave LaRonde Level 6

                          You're not thinking the shot through properly.  You're not seeing it properly in your mind's eye.


                          You want to put a display on the device screen?  You have to cut a hole in the shot where the display will go.  If it's a static device on a static shot, a mask will do nicely.


                          The display goes on the layer BELOW this one on the timeline, so it shows through the hole.  You'll probably need the Corner Pin Effect to get the perspective right.


                          So far, so good, right?


                          Now comes the foot.  It comes between the camera and the display, right?  So you see it nicely in your shot, right?  WRONG!  Remember, you cut a hole in that shot to show the display: when the foot passes through the part of the video with the mask, it disappears!  So you have to fix that.


                          The fix: add a new instance of your shot to the timeline, and make it the top layer.  Trim this layer's in and out points so it lasts only as long as the foot & leg obscure even the smallest portion of the display screen.   Animate a mask around the foot (rotoscoping).  Now the foot reappears as it should be.


                          If you don't think reflections are needed, screw 'em.  It'll save you a layer... not that it's that big a deal to make it look right, but you don't feel they're needed.


                          And how many different techniques are we up to, now?

                          See what I mean?  There's more to this special effects stuff than you think.


                          1 person found this helpful
                          • 10. Re: Compositing Challenge
                            theglennotf Level 1

                            Aha! I see. Thank you, Dave.


                            Well, your comprehensive answers will most definitely help others with experience in between yours and mine. Mylenium's, too. As for me, well, I think the most useful process for me will be to:


                            1. Paint the glass black
                            2. Get a good shot of the animation (or use the original animation)
                            3. Stage and film the shot
                            4. Send everything to a freelancer! ;-)
                            5. Wait for my son to go to film school


                            Thanks, Dave (and Mylenium).



                            • 11. Re: Compositing Challenge
                              Dave LaRonde Level 6

                              For some screwy reason, the web site won't let me edit my posts.  Where did I leave off?  Oh, yes: counting up the techniques you'll need:


                              Use of multiple layers.

                              Accurate masking.

                              Precomposing (that's for your display to go inside the hole.  You haven't even mentioned how you intend to make that yet).

                              Use of the Corner Pin Effect.

                              Modifying a layer's in & out points.

                              Rotoscoping (the big, nasty, time-consuming technique).


                              That's six different techniques you may or may not know about.


                              So to reiterate: this effects work takes a lot of forethought, and you have to be versed in techniques you may not have anticipated.  With the exception of the rotoscoping, these are pretty basic techniques ... and if you don't know 'em, you're hosed.


                              This isn't Microsoft Word, where you can dope out how to insert a table in the middle of a document from the Help section.  This is After Effects.


                              Early in its history, it was used pretty much exclusively by professionals who understood basics like interlacing, pixel aspect ratios, trimming clips, masking, applying effects, varieties of codecs, alpha channels, bit depth, nesting compositions... and so on.  They were used to complex, arcane multimedia user interfaces, like the one in After Effects.  Now it's used by a growing number of people who think, "Hey, it's just video.  How tough can this stuff be?" but the need to know the basics and the complex, arcane interface remain.  They're legacies of a different time and user base, and they've only gotten more complicated.


                              To know success, you have to deal with them.

                              • 12. Re: Compositing Challenge
                                bogiesan Level 4

                                Well done, Dave.

                                Let's go full retro and shoot this on a stage with a rear projection system bouncing off some mirrors and up through a hole onto the screen of the device.

                                • 13. Re: Compositing Challenge
                                  bogiesan Level 4

                                  There's also sophisticated editoing techniques. You can have one shot where the naimation is composited into the device's screen, cut to a closeup of the foot going up, cut toa closeup of the enraged foot owner, cut to a shot where the device has been swapped out for a practical but disposable prop that has one frame of the animation pasted under the glass.


                                  These types of practical, in-camera effects shots have been done successfully for almost a century.