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Posts Tagged ‘chroma key’

The third episode of my Fallen Star series was rather more laid back than the previous ones. There was no action, no big setpieces or fight scenes to implement, and much of the “plot” took place in a series of small rooms.

Despite that, however, there was a surprising amount of post production work required to finish the episode. Since a large proportion of our ship interiors didn’t physically exist, we had to use a lot of greenscreen. Any real locations we had available to us had to be modified to make it look like we were still out in space. One of the more ridiculous scenarios we encounter lately is having to shoot scenes across multiple days due to the mixed availability of our cast, and then having to composite them together into the same shot.

The below video demonstrates some of the visual effects work I had to do on Episode 3. I hope you find it interesting. And remember, the greatest challenge is in making something look easy.

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Here is a collection of visual effects sequences from my Fallen Star project, concentrating on the green screen (chromakey) sequences that placed our actors in artificially-generated environments.

From the start of the project, we knew we would be limited in which areas of the ship we’d be able to show, and that principally the episode would be set on the bridge. However, early on, I suggested we might try to expand the range of locations using artificial environments modelled in 3D, using a green screen to isolate the actors from the background. The possibilities were exciting! I set to work on creating some interiors, a long corridor, a hallway, a ‘transporter’ room, not to mention the fourth wall of the bridge. I used actual photographs of our real walls and carpets for the textures, to try to keep things as consistent as possible.

We were lucky enough to borrow a green screen for our project. Unlike normal green screens, this one was colourless until light is reflected off of it. Using an array of LEDs attached around the lens of the camera, we could reflect back the green light off of the screen. The light would only be visible from the angle of the camera and wouldn’t reflect off of the actors or props.

We had a few teething problems with this, however. At first, we set the intensity of the LEDs too high, and it did in fact reflect off of the actors. Therefore some of the green screen footage appears quite fuzzy or has messy outlines. We got better at the technique the more we used it, and most of the other shots have turned out fine. One advantage of using this reflective screen is that it doesn’t need to be as perfectly lit as a normal green screen would be – it’s self-luminescent. Unfortunately the actors did need to be lit properly, else they ‘silhouette’ against the background. We did our best with this, but ultimately I did need to lighten much of the footage in post-production. This meant that some of it has poor black levels and visible artefacts. Not a problem in Hollywood, but it’s difficult when you’re on a budget of nothing.

We used the green screen for every shot of somebody leaving through a door. This is because none of our doors were real. They’re either stuck onto the wall, or in some cases they’re entirely digitial. So the on-set filming would have been done first, with the character walking up to the door. Then, later on, the green screen shot was done, with the actor continuing to walk away, passing through or around an imaginary doorway. When edited together, it’s almost seamless. Almost.

The green screen didn’t extend down to foot-level, so the few times when we needed full body shots, the feet were removed by cutting around them with a masking tool. Thankfully, there wasn’t much movement, and all the walking shots were done from above the ankles. But even with a physically small screen, it’s possible to insert large background or shrink the actors down, as you can see in the video.

You’ll also notice that we sometimes separated our actors into layers. This wasn’t done for technical reasons, but rather logistical ones. We actually lacked sufficient costumes to film everybody at the same time. This led to the rather ridiculous shot of four people walking into the transit nav room in single file, which we filmed all separately! There were also scheduling difficulties, which meant not everyone was available for filming at the same time, so again, I worked around this by compositing two (or more) bits of footage together into one shot.

Ultimately, we couldn’t have made this film without a hefty amount of green screen, so I’m very glad to have had it. Perhaps we’ll be using it more in future.

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