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.