Sidepodcast - All for F1 and F1 for all

The magic of chroma key (part 1) - Reviewing how green screen works and how Sidepodcast uses the technology

Published by Mr. C

Seeing as there's a brief lull in the racing action at the moment, we might just be able to squeeze in a quick behind the scenes look at green screen technology. I should declare upfront that this post isn't remotely related to Formula 1, but a couple of people have expressed an interest in the inner workings of Sidepodcast, so please excuse the self indulgence.

The early years

The idea of keying out a single colour from a piece of film has been around since the 1930's. The principle is simple, pick a solid colour as a backdrop, ensure that it's not present in the foreground and then replace said colour with other footage during post-production. The techniques for doing this have dramatically improved in the last 70-odd years (while costs have drastically reduced), but the original concept remains the same.

Chroma keying is used in all forms of video production nowadays, the local weather programme is the most commonly seen example, but given its relatively low cost, there's little reason not to make some use of the technology.

That's me in the spotlight

Although we essentially have no knowledge of television production, when we started making videos it was pretty clear that chroma keying was a great way to turn a very small space into a larger one, and as all we had was a small space, it was worth looking into.

The first two videos we ever made for Sidepodcast didn't involve keying at all. Episode one didn't have a presenter while the second was filmed on-location. In the process of making these two short films, we purchased a copy of Final Cut Express, and hidden within its menu system was a tantalising option entitled 'Blue and Green Screen'.

Having the software was all well and good, of course, but to get started you need to own a coloured screen and we didn't have one. Neither did we have the budget to buy one. What we did have though was a blue duvet cover... so we used that instead.

Christine in front of a blue duvet cover

As you can probably tell, the early days were quite stressful. Apart from the fact we were making everything up as we went along, it turns out that certain blues are easier to key than others, even light is important and wrinkles in the background sheet can be troublesome. Oh yeah, and remember the principle rule of chroma keying? Ensure that the background colour is not present in the foreground!

The picture above tells a sorry story. It wouldn't be possible to create a worse keying set than the one we managed to even if you were doing so on purpose. Yes an iron wouldn't have gone amiss, yes more lights were required and yes the collar on Christine's top is blue. What of it?

Saving grace

All was not lost though, because technology is a wonderful thing, and with a lot of tweaking we managed to fashion something out of what we had. The final edit can be seen in last year's Bahrain preview. It helps that the video isn't very big, but you can clearly see that the once blue collar is now a peculiar shade of green, and there's a funny aura around the girl where rough edges were over-softened to remove troublesome artifacts.

That seems like a pretty good place to end the first part of the Sidepodcast chroma key story. In part 2 we'll look at how things improved once we bought ourselves a decent curtain.