Category Blog

Ever wondered how a green screen worked? Or how they actually make a Kaiju appear next to the Golden Gate bridge so realistically? Once the animation and FX are created, it’s up to the compositing artists to put everything together and make it all look like it was supposed to be that way.

Green and Blue Screens

If you’ve ever watched a behind the scenes video for a blockbuster film - in particular a superhero or an action movie - you’ve probably seen a lot get shot on a big studio stage with a bright green or blue background up on the walls. This is called a *chroma key* screen, and its sole purpose is to make it easier for the VFX artist to remove the background from the original shot footage (known as a *plate*) and replace it with something else.

But why is it bright green or blue? Well, technically speaking, any color could be removed - but these two colours are most common because they don’t naturally occur in nature at that vibrancy. Because of this, it’s easy to isolate compared to say, red or orange, which are tones that can be found in a huge amount of things - for example, skin!

So how does it work? Well, a machine is used to isolate that particular hue, and create a matte which acts as a very versatile cut out of the image. These days, it can be done with visual effects software on a computer, but before that this kind of work would have needed to be done on the Optical Printer, which I briefly talked about back in the Animation and FX episode. Once the desired subject is isolated and a matte is created, the background can become transparent and you can do pretty much whatever you want with it.


Sometimes a chroma key background isn’t possible for some reason - or maybe it was poorly lit, which makes it more difficult to be isolated. Or, maybe there was just something in a regular shot that wasn’t supposed to be there, like a water bottle or a logo. In cases like these, the only way to isolate the desired person or thing is to cut it out manually... frame by frame.

This is called rotoscoping, and it is probably one of the most tedious things in the world to do. Think about it, the roto artist has to accurately and smoothly cut the object out of all 24 frames in a second of shot footage. This is really hard to do well, especially if the shot was captured with a lot of movement or isn’t a high quality. Thankfully, the tools available to do this work these days are pretty amazing and can help take some of the burden, but it’s still a very detail-oriented task and takes a certain level of skill to master.


Once everything has been cut out, matted, isolated, or what have you, it’s time to put everything together! This phase is called compositing, and it’s where the final image is created.

Kind of like a puzzle, the comp artist has to take all the pieces and make them look like they all belong together. They’ll take backgrounds, plates, objects, people, animations, effects... you name it - and create a composite. Many times they’ll need to do some lighting and colour correction on some or all of the elements in order to make this work, making this a very technical and detail oriented job. Knowledge of color balance, composition, lighting techniques, and of course all the available tools is essential!


Finally, we can render the final shot and send it to the editor, who will put it back in his or her timeline for the final edit of the film. Depending on how complicated the shot is, this could take quite a while. It’s important to have very *very* powerful machines if complex VFX are being done, otherwise you’ll be waiting days or even potentially weeks to actually see the shot!

For example, when I created the 360 music video for Model M’s “Rock This”, nothing quite like it had ever been made before. It was a fully edited interactive music video with animated particle effects that were composited and stitched together. My base model Mac Pro couldn’t play it back in real time, so I was sort of working blind and had to render out small chunks at a time.

The final render took 9 days to complete. No joke. And being the perfectionist that I am, I of course realized that I had to go back in and fix a few mistakes that I wasn’t happy with... so that was a rough week.