Last week Josh and Kirstie showed you how to
build, light and shoot on a green screen. In And today we’re going to be talking about what you do once you get that footage back into the computer for compositing.
Now the techniques we’re talking about apply to any kind of green screen shoot but I’m going to
be specifically talking about this shot. Josh made this for the HitFilm 4 Pro launch
and it’s got a lot of cool stuff going on. Today I’m going to focus in on one specific
aspect, which is how we got the guy inside the helicopter. First up you need to remove the green screen background. Or, in this case, the blue screen, which we used because Geoffrey was
wearing a green costume. This can be done in HitFilm Express as well as HitFilm Pro. Now the golden rule with any kind of green screen work is that you want to maximise the separation between your foreground and your background. That just makes everything easier. And for the sake of your own sanity, if you’ve got someone in a green costume Just don’t shoot them in front of a green screen. Swop it out for a blue screen. HitFilm makes removing the green screen fast and easy. Once that’s done you can move onto the second stage, which is compositing that layer into
your shot. This is a particularly cool example because it shows off HitFilm 4 Pro’s unified
3D space, which makes it super easy to put layers in and around 3D models.
There’s no awkward masking or having to fiddle around with multiple layers and mattes.
You literally just put the guy…in the helicopter. OK! So let’s get into it. We’ve got a
blue screen clip you can download to try out the techniques for yourself, so check out the link on the info cards or down in the video description if you want to grab hold of that. We can’t actually give away the helicopter that we used in this shot because that was purchased from Turbosquid.com. But there’s loads of great places that give away 3D models for free which work really well in HitFilm, so check out places like TF3dm.com and Foundation3D.com There’s a load of talented people that put their work up there. You can just download it and try it out. After importing the clip, right click it and
create a new composite shot. This’ll set it up with the clip’s properties all ready
to go. So one of the cool new tweaks in HitFilm 4
Pro is that we’ve made the search box in the Effects library a bit cleverer. So if
I search for ‘blue screen’ it’ll find anything related to that topic, even if the effect doesn’t actually have that word in the name. First up we’ll look at the color difference
key, so drag that on to your clip. In the controls panel, make sure you switch the screen
color from green to blue, otherwise it’s going to get confused with this particular shot because obviously we’re using a blue screen. Now, this is our simple keyer, which you can find in both Express and Pro. But just because it’s simple doesn’t mean
it isn’t awesome. The general workflow with this keyer is to
first adjust the gamma to do your main removal. So I’ll drop that down until the bluescreen
goes away. Switching on View Matte makes it easier to see exactly what’s going on. I can now tweak the Min and Max sliders to clean up some of the fuzz in the background and foreground, until we
have this nice, clean matte. You can see that was just a few seconds to get that kind of quality key. Pro users also have the more advanced Chroma
Key effect, so let’s take a quick look at that as well. I’ll remove the color difference
key first, then drag on the chroma key. Opening this up reveals a much more advanced keyer
with a ton of options. This is especially powerful for complex or challenging composites.
So I’ll use the color picker here to select the blue behind Geoffrey. Incidentally, Geoffrey
is one of our genius web developers. He came all the way from France to work with us. He
also happens to look pretty intense when you put him in military fatigues. Which is, you
know, kind of handy for the stuff we film. Picking out that blue colour has got us a
pretty great key right away, without even touching any of the other controls. In the
effect’s View menu you can switch to the Matte view, then adjust the gain to get the key tuned in. Down in the Matte controls you can then change the clip background and foreground to clean
it up. It’s a similar process to the color difference key and in this example that’s kind of all you need to do. We don’t need to use the other settings this time round, but it’s good
to know they’re there for when you’ve been given a really tricky shot to work with. So if you find that the color difference key isn’t quite doing what you need, make sure you load in the chroma key and really go to town on it. So, what about all this stuff around the edge of the bluescreen? Well, that’s where
masking comes in. You’ll note that this was all shot very carefully, so that the parts
of Geoffrey that weren’t in front of the blue screen barely move – his feet and left
hand. All the parts of his body which are moving extensively are in front of the blue screen.
That’s going to save us a ton of time. Up in the Viewer, select the pen tool and then click
to start adding points to our mask. We’re going to draw loosely around Geoffrey – this
can be a pretty rough and dirty mask, because we know he’s going to be composited inside
a helicopter where you won’t be able to pick up on the details.
Once the mask is completed it combines with the chroma key, resulting in a really, really
clean key. You’ll also note that adding the chroma
key and mask hasn’t really affected performance at all. This’ll vary depending on your system,
of course, but it’s always useful when common techniques like this work in real time. OK, let’s move on to step 2. We’ve got our perfectly keyed actor, so what do we do with him now? Well, we can put him anywhere.
Such as, in a helicopter. I’m going to keep this relatively simple,
so I won’t be going into how to set up 3D models and lights and cameras. What I’ve got is a composite shot containing
an animated helicopter sliding into frame. It’s all ready to go and we’re going to put our freshly keyed Geoffrey
inside the back of the chopper. From the Media panel I’m going to find the composite shot containing the keyed clip and drag it onto the timeline. There it is, now functioning as a simple 2D
layer overlaid onto the chopper. I’ll now switch the layer from 2D to 3D
using the dimension selector on the timeline. OK, but this is actually to be expected. You see, what’s happened
here is that the keyed layer has entered the 3D space as some kind of gigantic Frenchman.
If I switch out to the perspective view you can see what’s really going on, with Mega-Geoffrey
towering over the helicopter. HitFilm of course doesn’t know what kind of relative scale these layers should be to each other. So let’s position and scale him up more appropriately.
First up, still in the perspective view, I’m just going to slide the layer backwards until
it intersects with the 3D model. If I move in for a closer look, you can see how the
keyed video layer is moving through the 3D geometry.
OK, I’ll shrink him down – about 4.5% seems about right. I can now position him back into
place. Because the 3D video layer exists in the same unified 3D space as the helicopter,
doing this positioning is pretty easy and obvious. I can orbit around the helicopter
if I need to, to get a better view of where it’s going An important step is to make sure we parent
the layers together. Otherwise Geoffrey has a horrendous accident as soon as we move the
playhead. So on the timeline I’ll open up the keyed layer’s parent menu and select
the chopper. This will lock the position of the keyed layer to the movement of the helicopter.
Just like that. Let’s switch back to our camera view, then
I’m going to turn my 3D lights back on. You can see we’ve ended up with Geoffrey
looking rather over-lit. This is because he’s being lit by the 3D lights in the scene because the keyed layer is now a 3D object in that scene. To make him look more realistic I’ll go and tweak his material properties. You can
see that he currently has quite a high specular value, which basically means the light shines
off him really brightly. And while Geoffrey is a shining light of the HitFilm office,
we don’t really want that in this particular shot. After dropping specular down it looks a lot
better, and I can then adjust the diffuse setting to get the exact brightness that matches
the surroundings. One super cool benefit of how HitFilm tech
slots together is that the keyed layer can also receive shadows from the 3D helicopter.
So if I turn on shadow rendering, you can see that as the rotor blades spin around, they cast
a shadow onto the keyed layer. That’s zero extra effort on my part as a compositor, but
it really helps sell the realism of the shot. You can, of course, use additional effects
to grade and blend layers together even further. The final shot mixes together a ton of other
techniques. OK – take a look at this. This is the shot
I’m going to be talking about in my next tutorial, but in the meantime the next video
is going to be Josh and Kirstie talking about some practical tips on how to shoot with lightsabers.
So that’s continuing our month of celebrating Star Wars. OK – subscribe if you don’t want
to miss it.