Greenscreen

Have you ever wondered how Superman appears to soar through the sky on your screen? Or how Harry Potter whizzes around on one of those broomstick thingymajigs whilst playing Quidditch? No, it’s not because of real-life super-powers or wizardry, it’s because of green screen.

It all begins during the production phase with the use of green (or often blue) screens/backdrops. These backdrops can be of almost any colour but green and blue work best as these colours are often considered to be the farthest away from skin tones.

The subject/talent will act or present (in the case of a newsreader or weather forecaster) in front of these large drapes of green/blue and a background will be added during post-production using some very clever technology and editing prowess.

On one of our recent shoots, the brief changed slightly whilst on set from shooting interviews with a plain black background to shooting them against a coloured background. We knew that the change would be very jarring in the edit, so we decided to do something about it and use the black background as a green screen, of sorts. Black is far from ideal though as it doesn’t contrast enough with the foreground content and therefore becomes extremely tricky to ‘key’ out in post-production.

‘Keying’ is the process of isolating a colour and making that colour transparent. This then allows another image to show through these transparent areas, transporting your subject from a London studio to the surface of Mars or an idyllic island in the Indian Ocean. But when the backdrop is of a similar colour to aspects of your subject, i.e. hair, eyes, clothing, then it becomes a more complex and timelier task.

So, what do you do when your green screen isn’t, well, green (or blue) …?

First, we tried Keylight within Adobe After Effects which is our preferred method and go-to option when working with green screen content in the past. It successfully picked out the background colour but also picked out similar tones in hair and clothing – not ideal.

Colour keying within Premiere Pro returned similar results, somewhat unsurprisingly.

Therefore, we needed to ‘mask’ around the subject which would essentially cut them out so that we could apply effects only to the background, but with so much movement in the shot, it became almost impossible to track the subject frame-by-frame. Despite lots of time and effort spent on this method, we just weren’t satisfied with the results, so it was back to the drawing board.

Next up, it was the turn of Adobe Mocha, which can be used to achieve far more accurate and consistent tracking but even this programme struggled with the similarities between tones.

Next on the list, Photoshop. Yes, video can also be used within Photoshop, believe it or not! But this very quickly turned out to be fruitless.

Finally, after much deliberation, we decided that going full circle and trying our luck again in After Effects was the only way we were going to achieve mission almost-impossible. We used an extremely clever tool called Roto Brush to separate the subject from its background. With the Roto Brush, you draw strokes on areas of foreground and After Effects uses that information to create a boundary between foreground and background elements. It’s not a one-click, job done process; it takes some fine-tuning and the use of the Refine Edge tool to create partial transparency around areas of fine detail such as hair but, with time, attention and a lot of patience, the results are astonishing. After Effects will even use the brush strokes that you have made and apply these from one frame to the next, even if the subject moves about on screen.

So, finally, we had managed to remove our subject from the green (black) screen backdrop and we could then place a new image in behind them (see picture) to fit in with the rest of the video.

This was by no-means a simple or straightforward task but putting in the extra effort and going the extra mile turned out to be the difference between a good video and a great video; or a happy client and a delighted client! Well worth the blood, sweat and tears!

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