Transcripts
1. Introduction: Hi. I'm Paul Trillo. I'm a Brooklyn-based filmmaker, and a lot of my work involves different types of effects and techniques in service, something a little more creative or different. One of the effects I find myself returning back to a lot is green screen and all the different ways you can use green screen. So what this class is going to look at is, not only the creative uses of green screen, but how to shoot green screen, and how to key it later in post production. It helps if you have a preliminary understanding of After Effects and a little bit of understanding of lighting. So what I'm going to use for the purposes of this class is a simple piece of green card stock, but I encourage you to find something different and new and surprise me so that we can really push green screen to new creative levels.
2. Basics of Green Screen: So, now we're going to take a look at what actually is green screen. It can of course come in many forms. It doesn't have to be a green screen. It could be green suits that could be used to create an invisible-man effect. Green screen can also be green tape or green makeup, a green image on a computer screen. It can basically be anything you can think of. One of the many reasons why green is used as opposed to other colors is digital cameras are very receptive to the green values. That means basically, when you're going to select and remove that green, it can identify more variation and you can get more refined with your selection. The other sort of practical reasons why green screen and not red screen or pink screen is that our skin that ranges more of the red hue will be easier to separate from a green background and because it's used outdoors a lot of the time, instead of using blue screen which is still used today. Blue also happens to be the color of the sky. Green is a color that is not as common, especially in wardrobe and other environments. What green screen allows you to do is isolate either a foreground or background object and it creates what is known as a mat. Think of it as creating a moving cutout of your image. So, if you were to take scissors and cut out your image but instead of having to manually cut out every frame, what green screen allows you to do is it removes your foreground or background elements and separates it. Green screen and visual effects are used on every single movie that's out there, whether it's just removing a car and replacing it with an older looking car or when you see a cell phone screen or a TV screen or a computer screen. Most of the time, what is being filmed in camera is actually just a green image that allows the post-production team to replace it later. It's used indoors in studios where entire worlds are created and post. It's used outdoors. Even by having an actor standing outdoor in the sun with a green screen behind them and then shooting a background image of the same shot and being able to place a monster or a car or whatever behind them. So, it's used in all environments indoors, outdoors. I encourage you to search for visual effects breakdowns of different films. In these visual effects breakdowns, you'll see how prevalent green screen is. So now that we have an understanding of the practical uses of green screen, let's talk about some of the creative uses. So I've used green screen or what is known as like Chroma Keying with different types of materials. One of the ways I thought of finding abstract ways to reveal the human body and show the human body was using fog and colored powder in slow motion and that turned into a project called Salience. So how I achieved this effect, it was relatively simple. Shoot the action of the person getting hit with the coloured powder and then you shoot a blank, what's known as a plate shot where there is no action at all and it's just a locked off tripod shot of your background and then the color that is being removed is replaced with the background image, so that all you're left with is the coloured powder that's flying into the shot and the person sort of disappears. I thought of using smoke grenades as a way of creating a sort of a hole in the image, a sort of just like you would have a star wipe. This was like a smoke wipe that you could continually transition from shot to shot with some sort of green smoke. So, I even used it in a hand-held way where I followed an actor hand-held wall. We also moved a portable green screen handheld and repeated the action multiple times and then in post, I was able to just make simple cuts between the different takes and have the same continuous background while the subject is constantly shifting. I also found other ways to experiment with green screen by combining green screen suits with a green screen background and cutting holes in the suits, so that all you're left with are floating pieces of the human body which also again, created a sort of eerie effect and a use of a green screen that was not so typical. Other use is also of creating essentially, a portal or a window. A sort of hallway of mirrors effect where I repeated the same shot within itself to create this sort of infinite zoom effect. So, out of all those examples, what we'll look into today is creating this portal into another world or creating a blank canvas for us to fill in later. Hopefully, you can take what's used here and run away with it, not necessarily saying you have to use it in this way but this is a way of thinking about green screen but maybe you hadn't considered before.
3. Coming Up With Your Concept: So, before you just jump into production and start shooting, you're going to need to do some sort of prep work, some sort of preproduction to help get your idea across. I do a lot of storyboards not just for myself and for my own benefit but also to help communicate my idea to the other people I'm working with. Film making is a collaborative effort, so it helps to have a clear storyboard or way of presenting your idea before you go into your shoot. Also when you are in the storyboarding phase it can help generate new ideas. So, when you're drying out your shot you might consider something that you wouldn't have considered had you just shown up with your camera. Whether it's a storyboard or a mock-up image. It doesn't necessarily need to be a hyper refined document. Sometimes it's as simple as cutting an object out in Photoshop and paste on another background. Whatever you have to do to help communicate your idea, but use this process as an exploration period where you can help yourself generate new ideas. If you are doing a more setup green screen shoot, I encourage you also to create a floor plan so that you know exactly where your subject is going to be, where you want to place the green screen and where you can place the lights. This helps your DP and all your crew know exactly what the plan is when you go into the shoot. Before you just go off and use some sort of random green screen effect, I would take a step back and think about why are you using this effect?. How does green screen specifically relate to your story, enhance your story, or what kind of poetic concept can you pull out of the green screen technique?. So for example, in the short film I did a truncated story of infinity. I found a couple different ways to use green screen. The short film is about the multiverse and so there's a lot of different versions of the same shot being used in a lot of repetition and so green screen help me remove the subject, isolate the subject, duplicate the subject, replace the subject, and it was sort of intrinsic to the story. So again, I encourage you to think about why you're using the effect and how it will benefit your story. Great. So, now take the time to figure out what your concept is, how does it relate to your story. Create a quick mock-up and then we can go and execute it.
4. Green Screen Materials: Let's start with the basic stuff you'll need to do this lesson. So, obviously we're going to need a camera, lens, tripod, batteries, you don't necessarily need a specific camera to shoot green screen, but there are certain things to consider when choosing your camera. The benefit of using higher end cameras is they give you more color range in the chip, so that there is literally more green information being recorded and a more refined key that can be extracted out of your image, so that the green can be isolated a lot cleaner. So, I'm using the Sony A7S2, which is a 4K camera. It will give you a nice result when doing green screen because it'll pick up a great amount of edge detail, even if you're shrinking it down to 1080 later, the 4K comes in handy when shooting the green screen. I also encourage you if you do have this camera or a similar camera to shoot log, log, slog or log c as a way of capturing the most amount of color information, and not baking your image with a camera profile that will destroy some of your green information. It's important to make sure that the tripod and the camera do not move that the head of the camera does not move and that the lens and focus does not move, that will be critical in being able to line up two different shots. This lesson will partly focus on using a piece of green board that you can find at your art supply store, but I encourage you to find other objects that are green to experiment with. So, green face paint, green tape, a green body suit, or even a collapsible green screen if you would like to do a full body green screen shoot. You want to make sure you avoid as many creases and shadows in this as possible, so pulling it nice and tight will give you a flatter surface and you can even steam it ahead of time to create a nice flush Green. If you want to jump into using green screen quickly, the fastest way is to pick up a piece of green card stock from the art supply store. There's anything from this sort of forest green to a neon green and both will give you the green screen effect, both will allow you to remove the background. However, there are certain greens that are better than others. You'll basically want a green that is in the mid range, so a green that's not too dark, and not too bright. If the green is too dark, there'll be a lot of noise information and you won't get a clean key of the green and it starts to blend in with the shadows. If the green is too bright, it'll also start to blend in with things and it also reflects more. So, if I hold my arm here, you might be able to see that the green is reflecting onto my skin a lot more because it's a bright object. If you have a more medium range green, it's less likely to bounce screen back out, when light hits it. Also a couple of things to consider when you're shooting green screen is how much variation of green is in your shot. So that means when you're shooting not to have too much shadow on one end and too bright of a part on the other end to make sure that it's as soft and flush as possible, you want to give your post-production tool a very specific hue to remove and post. So, as many ways that you can eliminate that in the production phase will help you in the post-production phase. Avoid green when possible in the wardrobe, make sure that what the subject is wearing is not too reflective and which it would absorb some of the green color and you would get what's known as green spill, green spill is when the green from the green screen spills literally, spills onto the subject's body, and then you get that really gross looking edges. Another thing to consider if you are placing an actor or a subject in front of a green screen is how far away they are from the green. If you're shooting with a green backdrop, you would want to keep the actor six to eight feet away from the green wall, so that none of the green will reflect back onto them. It also helps when lighting that you use separate light sources to light the green, and different sets of lights to light the subject, so that those two things exist in different worlds. If you are shooting in an outdoor environment or if you're using natural light from indoors, I would just make sure that that the green is not hitting the sun directly, that it's either angled in a way where it's flat or it's in shadows, so that again you're creating the most even green possible. If you are shooting a subject that requires reflective or white wardrobe, that is where lighting gets critical, where you will want to make sure as much light is pumped into the subject separately from the background and that you are using things like negative fill to help decrease some of the spill that's happening off of the background and the floor of the green screen studio. Once you're ready to move into post-production, I recommend using Adobe After Effects with the key light or color range tool. If you're not comfortable or familiar with After Effects, there are also plug-ins in Adobe Premier and Final Cut that allow you to pull green screen keys. Now that we have all our materials and we have our equipment, I think we're ready to shoot.
5. Lighting and Camera Setup: All right, so what I've done here is I took the green card stock that we got at the art store and placed it inside the frame so I cut it to fit the frame and what I have is a nice flush green surface with no wrinkles, no shadows. It's very clean and it's in a black frame which could come in handy later when we look into doing some motion tracking on this frame. It's essentially a blank canvas to be whatever we want, whether it's a piece of artwork that maybe we can't afford or a window into another world. It could even be some sort of infinite mirror into the same room that we're in right now. It's really up to you and I would use this blank canvas as a point of inspiration. This is a very basic setup for shooting a green screen, trying to get this evenly lit. So what I have here is a small diva light with a piece of diffusion over it so it creates a nice soft light, so that you'll see any shadows coming from this are relatively soft. The closer I get to this obviously, the harsher my shadows become. So again, that's a reason to have your green screen as far away as possible from your subjects. So yes, so again, lighting this with a separate light and the subject myself, is lit with a source light that is functioning just for me off to the side here. All right, so now that we have our green screen lit and in place, we're going to go through a few camera settings just to make sure that as we are recording this, we're capturing it in the most optimum way possible. So if you underexpose on the camera, you're going to get a very noisy key and you're limiting the amount of green variation that you're capturing and again, it goes for if you overexposed the image you're going to get a green that is no longer green, where the amount of green color information is greatly reduced and could potentially start to blend in with skin tone or other tones because you're trying to key a white. I can't reiterate enough that exposing your green screen properly is just as critical as trying to eliminate shadows and trying to place the lights in the right direction. We want to make sure that your color balance is set properly so that your green doesn't become too orange or your green doesn't become too blue and again, starts to bleed into other colors that may appear on the subject. So setting your color temperature on your camera to the color temperature of the lights is the best way to get the most clean solid green. So in here, you'll see as I change the color temperature on the camera, the green starts to change as well, so pay attention to what is the color temperature of your environment and what is the color temperature of your lights that you're using. If you are shooting anything that does involve a full-body shot in which you're shooting a whole subject against a green screen, a typical green screen shoot whether it's in a studio or your pop-up green screen, you'll want to not only separate the subject from the background for lighting purposes but it helps to throw the green screen slightly out of focus. If the green screen behind the subject is a little soft, it can help eliminate some of the texture of the green screen and eliminate some of the shadows that appear in the green screen.
6. Shooting Green Screen: One of the things we could do with just a simple green frame here is we could composite the same room back inside of itself as some feedback loop or infinite mirror. I could do a few camera moves on it to transition into that green full frame. So, what I'm doing is I'm I have a zoom lens on here and I'm zooming into the green full frame so that that green takes over the full frame and that gets us into our next shot. So, that green could be anything. It could be a portal into something. It could be a picture frame. It could be a manhole cover. It could be whatever you want. But if you move the camera to fill the green full frame, all of a sudden we've created a transition in camera. There's a few different looks that you could use when trying to do a camera move into the green screen. Let's say we want to have this whatever it is that's in this green screen track with the camera move. So, if the camera is moving and the green screen is moving, what we want inside of that green screen should feel as if it's moving with the camera shot. So, in order to do that we'll need to do something known as motion tracking. So, that looks for different bits of contrast in the image that the computer can identify and then track across the shot. So, we have a pretty nice high contrast image here where we have the green along a black border. The computer should have no problem tracking those corners of the green image and so that whatever we place in the green will stay motion tracked with the shot. So, as I move the camera back and forth, the image will stay trapped inside of it. It can tilt up and down. Whatever it is that's in that green screen will stay tracked and that's because we're shooting with a pretty high contrast object. If you are shooting with a larger full green screen wall and you want to add some hand-held camera motion or whatever it is to your green screen shot, you can always add cross hairs to the image, to either pieces of black tape or if it's a piece of paper you could draw x's on it with a pen and you can use those marks in post-production as a way of tracking the camera move later. So, another way of thinking about green screen is using it as a transitionary device. So, you could use a combination of green screen and motion tracking to move from one shot into the next. So, there's all sort of ways to use green screen not only as a way of isolating objects but as a way of creating transitions between scenes. So, now, you have an idea of all the different combinations of effects and techniques we can get out of a single piece of green board using not much setup time and only a simple amount of materials. Now, let's jump into post-production and see what it takes to start achieving some of these effects.
7. Editing Basics: Removing the Green: So, now that we've shed a few different options with our green screen, it's time to jump into post production. So, some of these same green screen concepts apply to both premier and final cut. However, I'm going to use Adobe After Effects, to get a more refined key, and dig into a little bit more detail. So, the clip I'm going to be focusing on is this nice long one where, the picture frame is both on the wall, and I move the frame around. I whittle down this 22 minute clip, just down to this five second clip that we're to use, just for this demo. It really doesn't matter how long the clip is, the effect is applied throughout the entire shot. Creating new composition, 1920 by 1080, call this Green Screen Portal v1. I'm going to take my, selected clip and, "Command C" and copy it over to the new composition, the 1080 composition. Now, this is a 4K clip. So, it's going to be, essentially twice as big as this 1080 composition. So, I'm going to need to shrink it down to 50 percent, and if I hold "Option, Command F", it'll automatically fit the footage to the composition frame. The first tool, I'm going to show you is a very basic, colorker which is Color Range. Color Range allows you to define just a very small, spectrum of the image, to essentially erase. Under Effects there's a whole folder here called Keying, and we'll go to Color Range. And it immediately starts to look for something to key, this is the wrong range to key. So, I'm going to take the Eyedropper here, and select the green, and it's already started to key out some of that green. And so we can kind of keep expanding this Color Range. So here, we're seeing some of the green still, it's coming through. Use the Eyedropper plus tool, this adds to my Color Range, if I use the plus tool and select more of that green, and you'll see now that more of that green is gone, it's deleted. But, as I script through it there's still some noise here in the green, and there's also a green edge, which I'm going to show you how to get rid of as well. But let's get rid of this little bit of noise here. So we're again, we're going to use the Eyedropper plus tool, and remove it once again, and that's looking pretty clean. Couple of ways to double check how clean your, key is. Is by placing different things into this hole. So, this black area that was once green, is not actually black, it is an Alpha channel. So it's essentially transparent in here. There's a few ways to check how clean that is. There's a Checkerboard icon here at the bottom of the composition window, Toggled transparency grid, if I click that it gets rid of the black and it shows, the Checkerboard texture is similar to what you see in Photoshop, and it's looking pretty clean. Other ways to check it, is sometimes I place a really bright solid color behind it. And that can kinda show me and if there's anything that I missed in my key. Yeah. It's looking pretty clean here. Other ways to, check what our Alpha channel looks like. The Alpha channel is again, the negative space in which there is a transparent coal. Right now, the composition is viewing the red, green and blue value. All the colors of the footage are being shown right now in the composition window. By toggle this down, and just hit "Alpha", that shows us, what our Alpha channel looks like. So you can see this black square, that was one green, is the the Alpha channel. That is the negative space. We can place whatever we want in there now. So first I'm going to play around with this hole in the image by, placing our clean background plate behind it. So this picture frame kind of becomes a window through me. So I'm gonna go back to, the source clip, and find that moment in time in which I cleared the frame, and kind of allowed for that, clean background plate. And all we need is a still. It helps if you run like a full 10 second plate, something that you can loop, with no camera movement, but because there's not much going on here, just still moment works. So I'm going to copy over this clean background, and paste it behind our footage. What goes behind goes, below the layer. Scaled too big, so I have to do "Option Command F", which brings our footage to fit the composition window. So now, what I have is this pretty fun effect where, as I lift the green screen window, I can see through myself. It looks like this background plate footage is not super long, and so, both these layers have the same file name. So, I'm going to just rename these. So, if I go to layer, time, and I do freeze frame. Now, I can extend this background layer as long as I want. And I can even extend, our footage, to carry on beyond. There we go. So now we have this sort of visible, window. This window through me, so you can imagine all the different things you could do with this. So, one thing I was mentioning before was that, we still see some of this green edge here. And there's a couple ways we can get rid of that, we could use Color Range. Try to keep, using the Eyedropper tool and removing this. There's still green, and there's still some noise in there. So, a very quick and easy way to, get rid of this green edge, is using the Matte Choker tool. So, under Effect, Matte we have, a few different Matte Chokers. I'm going to use the Simple Choker for now, this is the easiest one to use. Why it's called the simple choker. And the Simple Choker, it starts the Choke Matte at zero. So that essentially what it's doing, is it's expanding your Matte. So, if this alpha channel was a certain shape rectangle, what it's doing is it's expanding the borders of that rectangle. So as I sort of slide, this Matte Choker tool, you'll see that it's eliminating, some of that green edge. There we go, now it's nice and clean. If I drag it into the negative you'll see that it's expanding the opposite way, and we're bringing back some of our Matte. One other thing to keep in mind is that, the Simple Choker is, creates a pretty sharp edge, and if you want to do anything that's feels a little more organic, less sharp and less like digital looking, is we would use, I'm going to hide this effect. The other Choker tool is called Matte Choker. And, this does the same thing, it just gives you a few more options here so, you can expand and contract the Matte the same way as Simple Choker, using this Choke one label, sets it at 75 or something like that as the default. Which is usually about right. And then you'll see that there's also this geometric softness. The Geometric softness, is essentially affects how hard or soft the edges of your Alpha channel are. Again, I'm going to jump back over to the Alpha view here, to demonstrate that. And as I increase the Geometric softness, you'll see how this has become really round, and soft. And as I decrease it, becomes really sharp again. So the default is four, sometimes even that's too much, three and then you have this Gray level softness, which kind of is just a blur to the edge of the Alpha channels. So you can kind of increase that 3.5 here, increase the Gray level softness to something less harsh. And, we will increase the Choke too. Do this actually in combination with Simple Choker. Turn Simple Choker down to one. And there we go, we've eliminated all the green from our shot, and have a pretty nice organic edge to it.
8. Getting Weird: So, now, that we've got our green keyed out, we can basically do whatever we want. Few examples whether you can use just a still image, maybe it's a portal into some sort of rainbowy sky world. You could use some fire footage or really whatever it is that you want. You can really create some interesting effects as if like these are living photographs. Another fun GIF I've pulled, you can see as I'm moving this image around, how it's only appearing in the green screen thing. So, this is maybe, this could give you some ideas as to maybe there's layers of things that you want to bring in others it's the static plus this and you could animate this coming across. You could do really whatever you want inside here. So, I could have these two layers going at the same time. We could even overlay our fire footage as well. I can toggle this and set this to add overlay mode and all of a sudden we've just composited a bunch of our layers into some crazy world in here. So, you can see, you can really layer whatever you want in here. I'll turn up the top footage here, so you can see what's going on. There's our crazy world and here is our window into that world. Something you might be noticing is how as the green screen moves,the background is completely locked. The background is not moving with the picture frame. So, what we'll be looking to do later on is motion tracking, so that we can actually have this world follow it as if I'm holding like a TV screen or something. Another thing you might be noticing here is how as I wave my hands across the image, there's still some green edges that are appearing. That's due to the motion blur of the camera. So, it's adding some additional green variation into our key, something that our color range didn't pick up. So, the next tool we're going to be looking at is a key light, which can help create more gradation to your Alpha channel.
9. Refining Your Key: All right. So, let's get into key light. So, color range has got us pretty far when we're dealing with a very flat surface, when we're dealing with essentially an image with no to little variation of green in there. But what happens if we start to get more variation in green, more shadows are introduced, and more motion blurs are introduced. The tool to use when dealing with more of these variations would be key light. So, I'm going to find another piece of footage here that has motion blur and has some of the shadows. So, I'm going to copy this piece of footage over command C, copy that, this layer over, and paste this into our key light comp. Command V and front bracket brings it to the head, option Command F and it shrinks the footage back down, and here is a similar but different clip. Because it's similar but different, I could even copy and paste some of the work that we started with color range. So, here's a good moment where I'm crossing over. Also just a thing to note, here's my layer that we applied the green screen effects to. Got to turn the effects back on, this is a way to toggle the effects here. If I hit E, it'll bring up all the effects that we've applied. So, color range, simple choker, and matte choker. If we're feeling these effects, and these are working for us, I can hit Shift and select all three of these effects, Command C to copy those effects, and then if I Command V and paste those effects onto this new piece of footage. There it is. It's another window into the previous shot, and you can see even the other layers down here that are appearing. I can take this footage from below, and move this around, and really get artistic. So, just by applying a couple of facts and copying and pasting that I'm already able to create some pretty surreal looking stuff. But let's just say that this color range tool isn't really giving us the best key we want. You can see that this edge is still got some green, and it's so slight that it's going to be really tough to get out with the choking tools, because it's just going to make this look more and more fake. By trying this effect on and off, you can see what's happening. It's just not a very refined key. It's a little too broad. So, let's actually do away with these effects that we copied and pasted. I'm just going to delete these and we're going to look at our next keen tool, which will be key light. So, with key light, similar principles apply here. We'll start with our eyedropper, and select the green, or select whatever color it is you want to key, and you'll see that it's already it's introduced a bunch more of a gradient to our key, and so we'll work to get this to a place where we want it, or reset the key light again. Just so you guys understand the principles of this, I can eye drop anything in this frame. So, I can take this blue for instance it's on this book, and key out the blue, or I could even do something like keying out this, somewhat white wall, and boom. The white wall is gone. So, you don't necessarily need green to use these green screen effects, but you'll see how noisy this is and how some of these other colors will blend in with the footage of me, and so that's the benefit of using green, but again you can use this keen effect on anything. So, I'm going to reset this effect once more and select the screen. All right. So, basically, what's happening and there's too much transparency coming through this key. The benefit of key light, is that you get that transparency but you got to tweak it a little bit to get it to a place where you want it. So, again if I view my Alpha channel, here we're going to be working from this Alpha channel view to get a cleaner key. You want this to be white, and this to be solid black. You can see there's some gray in here, and there's a bunch of gray outside. So, we turn down the clip white. That will give us back some of the lighter green information in our image. So, that's looking pretty good apart where is our limit? Our limit is around 70 there. What all this gunk is, it's the shadows of my body falling onto the green screen. So, let's turning this off, you can see how I'm casting a very subtle shadow here. So, that's what's giving us that little bit of gunk there, there's just that variation that we want to get rid of. So, turn up the clip black, to get rid of that, and we're getting pretty close here, still there's some. Look at this book here. It's not a huge deal, I could also garbage math this, but this book has a little bit of green in it as well. I think I could fix it. I go. Alpha turned down our screen balance. It seems we have gotten rid of it, somewhat. So, go back RGB. Here is our new key. However, there's a couple issues that key light does. Not only does it create a key in the screen here, but it removes all the green from the image. So, I toggle this effect off and on. You'll see how it's not just clean out the green, but it's also removing green from the image. So, it looks like that wall is pretty green, and maybe it wasn't color balanced properly. You can also see how in my shorts down there it's affecting the color of that, and it's not necessarily a desired effect, it's also adding some noise to the image here that wasn't necessarily visible before I turn this effect back off and on. You can see how in a way it's destroying the image, because it's deleting this green and along with deleting the green destroys some other stuff. So, one way to fix that is, now that we have a clean Alpha channel. I feel pretty good about the Alpha channel there, but I don't feel great about the color of this. So, if I duplicate this footage and let me re-title this to green screen, key-light, duplicate it, and let's just delete key light again. Original color, and I'm going to use the alpha channel from this key light footage as the hole for this original color. So, this original color has no effects applied to it. I'll say I'm going to turn off all the eyeballs on this other stuff. So, there it is the top layers as key light, the second layer is the original footage, and we want to use the color from the original footage but the alpha channel from this new key light. Under toggle switches and modes, there's something called track matte here. This allows us to take the luminance or alpha channel of another layer, and you use it as the Alpha channel for this layer. I toggle this, and I do Alpha matte, and tell it Alpha matte green screen key light. So, it's important that the the layer that you want to use as your alpha channel is on top of the footage that you actually want to see. So, we don't want to see this key light layer, we just want to see this original color layer. But this key light layer needs to be stacked on top of this original color layer in order for this track matte to work. So, track matte, Alpha matte, Green Screen key light, and there we go. So, now we have the color from this original footage, and the alpha channel, the nice Alpha channel from the key light. Just bring back maybe this cloud footage. So, what I was talking about before when we were shooting, is you want to avoid green spill. In case there is any green spill like this, go to key in, and use advanced spill suppressor. It'll automatically remove the green from the shot. So, now we have a pretty clean key, and our colors are looking pretty good.
10. Infinite Mirror Effect: Again, we can do whatever effect we want. We can even duplicate our shot and shrink it down. We have these repeating affect. Quick way to duplicate this step, to create that sort of infinite feedback loop effect is, now that we have these two layers in a good place, Shift Command C will let us pre-compose these pieces of footage together. It'll basically combine these two shots into one shot and it creates a new compositions. So, we can also go to layer, pre-compose, and it'll take these two selected layers that I have, and make them one piece of footage. Because we're using the alpha channel from one and the color from another, it's essentially one shot and we don't want to have to deal with both of these layers. So, now once these are in a good place, I can pre-compose these and say, green screen composed, and now we have those two pieces of footage as one piece of footage. So, one of the benefits here is if I duplicate this, take the footage from below, the same duplicated layer from below, I could shrink it down, reposition this to fit inside, and then I can do it again, scale it down, reposition this to fit inside. Well, let's just do it one more time. Scale down. So that we get this hallway of mirrors or feedback loop effect. All were using the same piece of footage, same effects just duplicated. Now that we have all these four layers working together, you could do something where you could slide the timing of this so that there's even a delay in this, sort of echo. You can even play around with parenting these three effects. So, by using the Pickwhip tool, select these three layers and pickwhip to what you want to be the parent layer. So, basically whatever affects, whatever position, scale, rotation that you do to this top layer, these three will follow suit. So, you can see if I rotate or scale, these three will move along with it. I can do an infinite zoom thing just by scaling up the footage, so I'll set a position and scale keyframe, and scale up this footage a ton, drag it down, scale it up and you can see how we can do some pretty crazy effects here. We could even tell a story where whatever happens in each of these frames is slightly different. We can be zooming through this story whatever it is. These are just some loose concepts that you can play with using again, the same piece of footage. We could even scale-in further here into our next window, drag this out, scale-in even more to our next window that we're really diving in the deep there. Just for the hell of it, we'll take that fire footage, drag it up, scale the fire footage down, maybe we'll also parent this to our layer here. It's pretty awesome effects done in a relatively short amount of time. One thing I've run into when doing this zooming in effect is that, you'll notice that it feels really fast at the beginning as it's scaling up and then it exponentially slows down the more you scale it up, it's just the way aftereffects scaling works. So, to make this feel like a more consistent speed, select these two scale keyframes. We go to animation keyframe assistant and exponential scale, this will give us a more continuous speed on our scale. So, once I've done that it's created a consistent speed for the zoom but it's offset our position. So, I'm going to turn off these position keyframes and actually, if we're doing this zooming effect, if this is what you're looking to do, we can just change the anchor point into the point where we want to zoom into. So, using this pan behind tool, up here next to the camera tool, we can grab our anchor point. Our anchor point is this cross-hair that's in the center of the footage, and with the pan behind tool we can grab that anchor point and move it wherever. Basically, the anchor point is where the rotation, the position, where the scale hinges from. This is the anchor of the footage, so everything will scale outwards from this anchor point. So, if I set that as like a target to scale right up there, now, as the footage scales, you'll see it, it scales to where the crosshairs are. There we go. We've got a consistent zoom headed right towards the crosshairs of that fire. This helps if you're shooting with a camera width 4K so that we can scale into the footage significantly. But, because of the speed of this zoom, we can actually get away with lower resolution footage because it passes in front of your eyes so quickly. One thing to notice too as we're scaling into this footage, you can see how I come back in and across the frame there. So, I can just take this layer in which I'm entering the frame again and I'll just clip it so that it ends a little sooner so that I don't enter back in again. So, if you've made it to this stage, you've got yourself a pretty cool fun looking project. Again, using only a short amount of footage and not very many tools. If you're looking to do something a little more advanced where let's say, that picture frame is moving and you'd like to track footage into a moving picture frame, then we can move on into learning a little bit about motion tracking.
11. Motion Tracking: Now that we've learned a little bit about the fundamentals of green screen, keen and shooting, we're going to look at how to motion track in combination with green screen. So we're going to learn the basics of four-point corner pen motion tracking. So essentially what that is, is taking our footage of the green screen picture frame and being able to composite something into that picture frame that moves along with the footage. This is a preview of what we'll be looking to achieve, which is getting this footage to feel like it appears inside the picture frame, that it actually is part of the footage we shot. So, just to compare it to what we were doing earlier, this is like almost a window that reveals something below and what we're going to be doing is tracking the footage into that so that it feels like I'm actually holding a picture frame with a live image on it. I've got the same piece of footage here of the moving green screen frame and under window, tracker. So, in order to track this picture frame, since it has these four corners, it's perfect for perspective corner pin which gives us four track points. All we have to do is take this track point and put the cross hairs of that track point into the corner of the picture frame. Drag these to each corner. It's also important to keep the tracker points in the same sort of orientation that they are. So, track point one is going to go into the top left corner. Track point two will go into our top right corner. Track point three goes into the bottom left and track point four goes into the bottom right corner. You'll see there's two squares here. That kind of tells the tracker what information to look for that's similar. The way that a tracker works is that it finds similar information between frames and places a pixel where it finds the similar information. It's good to have the smaller square a little in a smaller region so it's looking in a smaller region and the larger square will look across the frame for more similar information. So, just expand the range of the bigger square. So that looks pretty good. So now that we've aligned this and we have our parallel lines that are running along the edge of the picture frame there, we'll hit the analyze forward and start tracking the motion of this. So, the faster these points move in space, the trickier it is for the tracker to find them but so far, it's still able to keep up. It helps when your motion tracking to have these large swatches of contrast. So, using the black picture frame really helps identify some of those contrasts points for the motion tracker. If you're trying to motion track two grey moving objects against each other, it's going to have a tougher time because the information is so similar but more contrast here, the easier this track works. You can see it's holding up pretty well up there. It went off course at track point one. You can manually grab it. If it goes off course, you can manually grab the tracker and move it back to the corner. Sometimes when the motion is too fast, the tracker has a tougher time and you'll see it go off course. I can just analyze frame by frame here. Since we're using 4K footage, it helps the track a lot because it's just more information for it to look at. Once we have our track more or less set, we want to make sure that all these tracker markers are then applied to a new piece of footage. So, I know that this picture frame was 18 inches by 24 inches. So, if I create a composition that is 2400 by 1800, the dimensions of that composition will match the picture frames so I won't be skewing anything or stretching anything. It's important that you roughly get the correct ratio of what your compositing into to match the composition setting. So there's our track after I analyzed the motion track and did a little bit of manual tweaking to it. We have pretty good four-corner pin track and I've created this new composition that's 24 by 1800. I'll drag that into this composition and under edit target, I will set that to comp one. This is the composition where we're going to be placing our footage. I can rename comp one to say place footage here. Great. So we have an empty composition and so I can bring in this fire footage. Maybe duplicate it a couple of times and even scale this up so that it fits our 2400 by 1800 composition and duplicate this across time. So there's our pre-composition. So this is what's going to be going inside the picture frame. Jumping back to our motion track. When we want to apply this motion track to the composition that has the fire in it, we will go to edit target and we will choose our composition that we called it place footage here. You click okay and then you just click apply after you've set that target. So, now we're not seeing anything. I think that's because our place footage here is below our green screen footage. So here now we'll apply it and you'll see that fire footage is now locked in with the picture frame. I'll do a little bit of manual tweaking. Some points when it moves really fast where these corner pins sort of misaligned, so we can do some manual tweaking here to get that to fill the frame. So once I've done that, now I have a pretty solid motion track of this footage. We can actually bring our green screen footage on top because it's green. Turn on our color range effects and now we have this fire footage existing inside the picture frame. It still feels a little false to me so we can do a couple of things here. We can add motion blur so that the motion blur of the picture frame is matched to the fire and that's as simple as toggling this little button that says motion blur, click that and then toggle in in the composition window, the preview for motion blur so we can actually see it in action. Now, you'll see the faster that this motion track moves, the more blur is added to the footage, so now it it appears as if that footage is actually in the shot. We can do some other things to help the compositing, such as some slight curves to the footage so that it's not too bright and then the blacks aren't too black. Just so that it feels more like a video screen image rather than a digital video screen. So, that was the basics of motion tracking, specifically motion tracking inside of a picture frame.
12. Wrap Up: So, now we've seen that using just a piece of green board that we bought at the art store, a camera, and a tripod, we've created a pretty interesting effect. Essentially, a infinite zoom through mirror effect. Some of the things we just went over include: how to use color range, how to use key light, how to use different types of matte refined tools, and also how to get a clean Alpha channel. Some of the things we learned after we keyed our footage, is how to take the Alpha channel from one layer and apply it to a different layer using track matte. After we use track matte, we learned how to pre-compose the footage, and duplicate it, and also, parent the same duplicated layers to a master layer, so that when we animate one thing, it affects the animation of the duplicated layers. Finally, we learned how to scale that footage to create that infinite zoom effect, and to create a consistent zoom, using the animation preset exponential scale. So, that is the fundamentals of green screen, and hopefully some weird things that we can do with that green screen, so not just the typical uses. I think that's the point of this class is that there are many uses of green screen beyond just putting a character in some fantasy land that we can actually find some creative uses of it. So, I encourage you to take some of the fundamentals we learned here, even with the infinite zoom or some of the camera moves, and apply that to the screen-screen effect. I'd love to see even uses with the green screen suits or other green objects, and finding fun ways to play with that stuff. So, yeah, looking forward to seeing your projects, thanks for watching.
Paul Trillo, Filmmaker
