In this blog I thought I’d continue on some of the techniques used in visual effects.
A lot of effects in movies are actually 2d mapped onto environments or 2d images used to hide unwanted items. They’re also used to replace things like posters and number plates.
In my last blog I talked about the effects of creating the rabbit, the rabbit was one of the 3D effects in the film. There aren’t that many 3D effects used in The Great Spielron but I had to use 3D for one of the more gruesome scenes where some of our characters get a knife in their heads.
I’ll break down one of these shots, it’s where Katie throws the knife and it hits Mike square in the forehead.
When deciding the best approach for an effect I think it’s always best to ask the question “can this be done on set with real practical effects?” If the answer is yes then I always think this is the best approach as it doesn’t matter how good the effect is in CG, it’s never as good as a real prop.
Obviously for this particular shot that required a knife to be thrown, the answer was most definitely “no” we can’t use a real knife…well not unless we didn’t need our actor anymore, but we did so we decided it was best not to really kill him. So the choice was to do it in CG (computer graphics).
This actually posed a problem when filming, as I realised we couldn’t even use a proxy object when Katie goes to stab Kevin in the head as even something soft like a foam knife would still hurt if it hit you in the eye. So I had get them to act and react with nothing at all. It also didn’t help that it was about 12:00am and so we had about 10 minutes to wrap up the whole end scene. Everything in that last part of the movie was finished in about 15 minutes. We just went handheld and tried to get as much shots as we could. Anyway I’m digressing.
Now on a big budget film there would be time set aside for the VFX supervisor to take measurements and measure lighting info, using things like a big chrome ball and a big grey ball. You sometimes see these on the making of movies. Basically what these do is allow the VFX artist to work out where the light is coming from and how intense it is. By taking photos at different exposures they can then put this information into the computer and the lighting they get is pretty accurate to what was on set. It also allows them to have reflections that match too, so the whole CG elements fit to the environment.
We didn’t have time to do this, I brought the chrome ball but we were so rushed that it never got used, I had to rely on my eyes to try and get the knife to match the real footage as best as possible.
One issue with using 3D elements is you can’t use the more basic technique of using 2D trackers to match the 3D element. If you don’t know about 2D tracking you can view one of my latest blogs about it here https://22dayslater.com/2014/05/19/its-all-in-the-eyes-the-zombie-eyes/
Actually that’s not completely true. If the camera isn’t moving around the object too much then you’d get away with this, which is something we did for out low budget one day horror that you can see here Because the real footage was being seen from a pretty flat on view I knew that I could use a 2D track to basically “tack” the 3D animation to a point on the screen.
But for the shot of Matt, his head moves quite a bit and we see it from quite a few angles, so I knew the knife would be seen from many different angles as well.
This is where a different technique has to be used which is 3D tracking. Like 2D tracking it uses points on the screen to work out how things are moving. But unlike 2D trackers it triangulates using special algorithms to work out things like the Z depth of where things are in the scene. Although a lot of 3D trackers have automated settings, these usually only work on simple scenes. If a scene has a lot going on, with a lot of camera movement, it’s sometimes necessary to give the tracker more information, for example the focal length of the camera. Sometimes you’ll see on the making of movies little markers, especially on green screen sets. These markers are a good way of showing the computer points to lock onto. 3D tracking is a real art in itself and something that can take many attempts to get a good result.
To track Matt’s head, I imported a 3D mesh that was similar to his head and scaled it to fit the real footage. The 3D tracker could use this as a way of marking where it needed to be in the footage. You can see this in the video below. Excuse the “Demo mode” I only have a demo version of the capture software
Now that I had the information I could map the real footage onto the 3D mesh and add a 3D knife. Below is an image of the 3D knife un-textured.
It was then simply a case of animating the knife going into the 3D head. I added lights that looked about right to where they would of been in the real set and also added shaders to the knife so it looked like its real life counterpart. Shaders are a way of telling the computer what material an object is made of, basically how it will react with light. So in this case it was a stainless steel knife so needed to be very reflective.
The last thing I needed to do was to add a trickle of blood that ran down Matt’s forehead. To do this I used some of the fake blood we’d made up for the scenes with Katie and the hat. In case you’re interested, making fake blood is very easy and involves Syrup, red food dyes and coffee.I might do a blog on that at some point.
I shot various version of this fake blood pouring down a green screen as you can see below
It was then a case of removing the green and cropping just one trickle of blood. I used a 2D tracker so that it would stick to the movement of Matt. And as a final touch I used a tool in After Effects to bend it slightly so that it looked like it was following the contours of his face.
The last touch was to add a shadow to the area around the knife.
Here is a clip showing the different layers.
And here is the final result
The other knife shots were achieved in a similar way. The only other thing worth mentioning is I added a slight blood burst when Kevin gets the knife yanked out of his head. This was a mixture of using stock footage and also a dust hit that I tinted red as I wanted to get that faint spray of blood you’d get if it was real.
So that’s that till next time.