BMPCC4K – Green Screen

In an earlier story about the ongoing development of my cinema rig, I posted a video where I used green screen technique to introduce a background to what would have otherwise been a bland setting (with Winter afoot, nothing outside is looking that great). This ‘green screen’ technique is as old as the hills, but previously has been less than accessible to most people with a video camera. The green screen material has certainly been readily available, but the video processing software has not been quite so easy to come by and, where available, has often been expensive. But with new software options and especially software such as Blackmagic Design DaVinci Resolve, it’s pretty much available to anyone who wants to experience this frequently used Hollywood technique. And frequently used is an understatement, as just about every film made nowadays involves some or a lot of green screen technique.

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Green screen technique – (source: Fame Focus)

Before attempting my first green screen effect, I studied many YouTube videos on the theme and every one of them went into great detail about the need for evenness of the screen as well as absolutely even lighting. I could understand the desire for this, as shadows caused by wrinkles etc and uneven lighting would make things more difficult to remove in the software. However, when I looked at what Hollywood was doing with the green screen techniques, their setups were anything but wrinkle free and evenly lit. If you’d looked at the many examples of behind the scenes views available on Google, there wasn’t this fastidious attempt for perfection by any means. So when my eBay green screen arrived, folded into a small package and replete with folds and wrinkles, I put it through a brief rinse and spin cycle in the washing machine and then hung it up on my existing background stands to dry out in our lounge room. Being Winter, the heat from our fireplace was ideal for slow drying and when the wet spots eventually dried out and most of the wrinkles disappeared, I was ready for a bit of experimenting.

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Green Screen Setup

Australian Image Photography

Green Screen Setup

Now even the rinsing and drying didn’t remove all the wrinkles, but with some tarp clamps holding the edges slightly taut, it wasn’t too bad. Lighting was another issue altogether and at this stage I wasn’t going to buy any additional lighting until I knew that things would work and that additional lighting would make a substantial difference. So for the beginning, all I did was place an existing 45cm square LED light, ones used to imitate a skylight, on the floor pointing upwards to light the screen. It wasn’t the most elegant option nor by any means set up like so many stated was required, but I had nothing else available and nothing to lose at this point in time. Anyway, despite the relatively inelegant setup, the effect worked far better than I expected and demonstrated that it wasn’t that essential to get everything perfect. Now clearly if I wanted to take a wider aspect shot of the green screen, then I would need extra lighting as, even in the test, you could see the light highlighting my clothing from underneath and not isolating me fully from the background.

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Green Screen Setup

56W (>3000 Lumens) 45cm x 45cm LED Light Panel

56W (>3000 Lumens) 45cm x 45cm LED Light Panel

But for a first attempt, I was more than surprised at how well things turned out and how easy it was to create the background effect with DaVinci Resolve. It was simply a matter of selecting the green, making a few adjustments and adding a still image for the background and within minutes I had a half decent result. There was of course more work involved getting as much of the spill out of the metal parts of the rig and the fur of the microphones. Some of these issues can be fixed by moving further away from the green screen and of course with improved lighting, as well as subject positioning. It’s all a learning curve, but I am still amazed at how easy it is to accomplish with such a simple setup. However, one of the biggest issues that I have is finding a good place to set things up. The green screen that I bought is 3m x 3.6m and this requires a pretty large area if fully deployed. In the earlier video example, I had the screen draped over the cross-beam of the stands so that it was 3m wide but only 1.8m high. There just never seems to be enough room to set these things up and be able to move about properly. To have one large empty room for a studio setup would be great.

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Green screen backdrop

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Green screen result

So for my next attempt I decided that better lighting was in order to illuminate the green screen. The 45cm LED was great for illuminating the subject, but not ideal for the green screen. So once again I hit eBay and found exactly what I was looking for, that being some LED slimline batten lights, a new take on the old style fluorescent lighting strips, only much lighter and slimmer. These were 1200mm long, 40W, 240V units and at <$24 each (delivered), two were just what I needed. The BMPCC4K white balance reading indicates that they are 4750K and with a 120 degree light spread are ideal for lighting the green screen. To hold them up, I also bought two very cheap adjustable lighting stands at <$23 for the pair and, with a length of aluminium strip, was able to easily mount the lights to the light stands. All that I then needed to do was connect the wiring to some 240V plugs (using existing power cables of which I had plenty) and job done. Once finished, the light units look like they were commercially designed for the task.

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LED Strip lights and light stands

Australian Image Photography

LED Strip lights and light stands

Australian Image Photography

LED Strip lights and light stands

The background used to replace the green screen can be anything you want, but it’s important that what you superimpose has the correct perspective and lighting to what you’re filming in front of the green screen, else it can look odd if light and shadow come from different directions in the foreground and background images/video. In the case of this story, I decided to take a video at Mossvale Park while taking my hounds for a morning run. It was very early morning and very cold, with the sun streaming across the park from a low angle, casting long shadows and illuminating the frost on the ground. So I had to keep this in mind when setting up the camera and lights back at home. I needed to emulate the low sun with the lighting setup and have the camera at a similar height and angle. This also meant working out my distance from the green screen as well, so that not only did I get the right perspective, but also make sure that the light didn’t come back to me from the lights illuminating the green screen.

And by using Blackmagic RAW in my BMPCC4K I get far more flexibility with post-processing, so when it came to combining the two videos and replacing the green screen with the park video, I used DaVinci Resolve Fusion to make the job much easier. My first attempts using the Colour panel worked, but involved a lot of unnecessary fine adjustment and still didn’t give great results. I did it this way following a YouTube tutorial, but then found another one that gave easy guidance for using Fusion and the results are significantly better and easier to achieve. I’ve since found a few more, but the one linked is pretty good and not too long. Now Resolve offers some amazing features for video production, but a lot of it can be a struggle to wrap your head around and, unless you need the features every day, it can be mind boggling to learn. Thankfully, most of the daily things you need are very easy to grasp and there are plenty of videos explaining how to do things in Resolve. Once you get the hang of the features that you need, it’s a truly enjoyable product to use.

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