How do you remove a background from a videoclip so you can make it appear as if the foreground is taking place in a completely different setting? Keying or chroma keying is the answer. What used to be very difficult to do, has been made a lot easier with applications such as Shake and Motion, but it can be made even easier than this: with the PHYX Keyer, DiffKeyer, LightWrap, ScreenCorrector, and Despill plug-ins for Final Cut, Motion, and After Effects.
PHYX Keyer is a FxFactory plug-in, so it will work across all supported applications with one license. The chroma keying system PHYX uses is pretty advanced. It consists of five elements. You’ll have to choose one system — either keying straight or using a clean plate and keying based on differences — and then fine-tune the results with Despill and LightWrap.
What you’ll need first is of course a blue or green screen. These can be made of any sort of material, provided they are smooth (no textures) and evenly coloured in a bright blue or green tint. An even lighting is essential too. Take a look at the test video clip I made. It uses a cardboard green sheet of paper, lit using daylight only. The green screen setup that I used for testing purposes is handy for stop motion projects or for shooting small objects/scenes.
PHYX in Motion
With PHYX version 2′s Composite Matcher, your screen doesn’t even need to be that perfect anymore. Composite Matcher enables users to correctly match colour and tone of backgrounds, making composites even more realistic.
Also new in PHYX 2 is FastKeyer. This contains all the basic tools needed to perform keys quickly and efficiently. It contains chroma reconstruction technology to accurately key 4:2:2 or 4:1:1 footage, RGB Keyer, Despill, and LightWrap plug-ins within one simple interface.
MatteFuse allows users to combine mattes to create the ultimate matte for each element. You can input multiple mattes or masks — up to 8 of them — with full control over inverting, Luma scaling, and application method (minimum or maximum).
A great tool that is my personal favourite is the ‘Edges’ Mode in Despill. It’s a new PHYX 2 feature and it allows you to process only the edges of a keyed element. It prevents Despill from removing green or blue within the foreground element, allowing full control of the areas to despill. Despill now also contains multiple algorithms for processing blue and green.
If you want to shoot action involving people it is a matter of course your screen will have to be much bigger — about as big as the room where the action takes place. You can of course buy a green-coloured cotton sheet and hang it in-between a couple of step-ladders, but a little more professional are green/blue screens from VFX Screens for example.
Once you have shot your scene with a properly lit blue/green screen, you’re set to start tampering with the values in PHYX Keyer. I tested PHYX in Motion, because that works the quickest — actually, PHYX is very fast, in whatever program you care to use it, and much faster than Shake’s Primatte!
Keyer offers three Keyer Types: YUV difference, Channel keyer, and 3D keyer. Other parameters include chroma reconstruct, YUV color, YUV treshold, YUV smoothing, and then yet other parameters depending on the system you’re using, such as density, boost and contrast settings.
The modus operandi when you’re not a professional keying artist is to experiment with the sliders and continuously get feedback from the (very skinny) documentation. This is the guaranteed way to learn keying quickly.
The results that you’ll get out of PHYX are first-grade. After only a couple of minutes I was able to create a satisfactory chroma key in the test file. Fine-tuning in order to get a perfect one took more time: about half an hour later I felt I got to the best results I was going to get out of PHYX Keyer.
My tests involved keying with the straight Keyer (which turned in the best result), keying using a clean plate and DiffKey. The DiffKey experiment resulted in a worse matte because I wasn’t able to get the lighting right — remember that I only had daylight to work with. There was a very noticeable tint difference between the original scene’s geen screen and the clean plate, shot afterwards.
This made it impossible to get the same results with PHYX DiffKey as the one I got with the usual Keyer.
The Despill and LightWrap modules further refined the matte that I had created with the Channel Keyer. The result is stunningly accurate, especially as I feel that with a better lighting and some more time spent tuning the PHYX Keyer parameters I could create a really spot-on matte. In PHYX 2 the LightWrap plug-in is even more powerful with increased speed and control.
The million-dollar question is whether PHYX Keyer is worth the investment; after all, you get keying algorithms for free with Final Cut Pro, Motion, and even After Effects. The answer is that none of these offer the flexibility of having three different methods and two different systems all wrapped into one system for a low price tag. In fact, none of the other keying systems that you can buy as separate applications, offer what PHYX offers at a price of approx. 150.00 Euros.
