Noise, Sampling, Codecs and Green Screen: A Potential Horror Story

DV Info Net by Art Adams

I’ve done a lot of testing with the Sony F55, and I’ve shot a couple of 4K projects in XAVC, but until recently I hadn’t used this camera for green screen. Sony’s implementation of XAVC uses 4:2:2 sampling, which can cause a lot of problems for green screen compositing, so when I got a call to shoot a green screen project with an F55 I decided I had to do some testing. Here’s what happened…

I have a love/hate relationship with the F55. It has the potential to be an amazing camera, and it certainly offers a lot of bang for the buck. The new LC-709 Type A look profile, which makes the image look a lot like what I’d get out of an Alexa, produces stunning images and gorgeous flesh tones, and Sony raw is pretty awesome—especially at high speeds. Unfortunately the menu system is one of the most complicated in the world, full of subtle landmines and booby traps, and basic functionality that I can find in Alexa–such as internal 4:4:4 recording to ProRes and the ability to white balance in log mode–are lacking.

Lack of white balance is particularly troubling for shoots under mixed light: normally I’d gel my tungsten lights green to match background fluorescents in office buildings as I can then white balance to remove the green cast, but the F55 doesn’t white balance in Cine-EI mode. It offers three presets–5500, 4300 and 3200–but as of software version 3 there’s no way to remove green overall. (This appears to be the same in v4 based on a recently released manual.) This means that my clients have to watch a green image unless I can wrangle an expensive additional box on set to manipulate the monitor feed in real time, which doesn’t happen as often as I’d like.

I’ve shot a lot of projects in XAVC 4:2:2 and not had any problems, but they’ve all been live action and most have been WYSIWYG. My only SLog2/SLog3 projects have been shot in 4K or raw. Codecs get away with quite a lot when compressing an image as our eyes are easily deceived when it comes to color perception and sharpness, but green screen is another story: suddenly it’s all about the edges and how clean they are, and all a codec’s faults come to light. read more...