By Jeff Foster
If you’re new to green screen keying or just dissatisfied with the results you’ve been getting – hold off on calling NewTek tech support until you’ve examined your production process. 90% of a successful chromakey is done before the image appears on your screen in your TriCaster Studio!
Do you have the proper materials for your background? Is your lighting setup for the background and your talent correct? Have you measured your lighting and background to be sure it’s even? How’s the exposure coming through the camera? What settings in the TriCaster Studio keyer work best to provide a clean key?
I’m going to cover all of these elements in 5 steps here and link to more detailed breakdown of each step along to way for a more in-depth study from other articles I’ve written for the NewTek Tip Jar.
- Background Materials
You can use many materials for green screen and blue screen compositing, depending on your location, the scale of the project, the method of keying you’ll use, and, of course, your budget. Large-scale projects such as motion-picture production use huge sets with seamless painted walls, cycs, and floors—not to mention a vast array of lights. On the opposite end of the spectrum, a low-budget independent video project or interview may use a pop-up green screen or even a piece of green material suspended from a rod or frame, with a couple portable lights. In either case, knowing what you need to accomplish and doing some prior planning will help you get the most out of the materials you have at your disposal.
The single most important factor of your choice of background material is the color. Many manufacturers produce off-colored shades of green and inferior materials and paint pigments. If the paint or fabric has too much blue, yellow or red in it, then you’ll be fighting with trying to get a decent key, no matter what else you do.
Skip going to the hardware store or fabric store to get your materials. If you’re on a budget, this is still the one place you really can’t afford to skimp. At minimum, get photographic green paper from an actual photography store/supplier and light with green bulbs. Just be sure you can control the amount of light on it and can still position your subject well in front of the background to eliminate green spill from the lights.
It’s still best to use a quality fabric or digital green paint whenever possible. Supplies from Composite Components Company would be my first choice and a Lastolite portable/reversible pop-up would be my next option. Forget the cheap kits you’ll find online – they’re a total waste of money.
To get more detailed help with your background materials, check out my Best Green Screen Materials article in the NewTek Tip Jar!
- Lighting the Background
There are as many creative ways to light a green/blue screen background as there are camera angles and scenarios. But you must follow a few basic rules for favorable results, no matter how big or small your project is. You can also use several types of lighting systems, in different combinations, as well as shoot against a screen backdrop outdoors.
The green background must be evenly lit, or shadowed areas will be harder to key out. This is especially true for backgrounds behind fine hair or transparent items such as glass or liquids. The subject you’re keying out needs to be far away from the green screen so you don’t get spill from the reflective light off the screen onto your subject. In addition, the subject in the foreground must be lit separately so you have control over the exposure and direction of the light source(s) you require for your scene.
If you’re using smaller tungsten video lights, compact LEDs or LED Panel lights, you will need to be sure you have enough lights in place to fully cover the green screen evenly. This is a more difficult process as it takes a lot of effort to avoid hot spots and shadowed “drop out” spots where the screen is under exposed. Remember, EVEN lighting is the key!
The three essential lights are the Key light, the Fill light, and the Back light. If you’re doing simple interviews or a talking-head shot in a studio, the layout of these three lights as shown in the diagram above will probably be sufficient and pleasing to the viewer because it’s most flattering for your model or subject.
The Key light is your main light. This is the predominant light source on your model and should be positioned to match the direction of the strongest light source in the background to which you’re compositing. For instance, if your subject will be composited into an outdoor scene with strong sunlight, you need to match your key light to the direction the sun is shining in your background footage. Matching the color temperature and intensity is equally important. If you’re compositing your subject onto a scene that’s supposed to be under a streetlamp on a dark corner, then the same concepts apply, but the direction and intensity of the light source should be much different.
The Fill light is just as its name suggests: it fills in light throughout the scene. The position and intensity of this light (or several lights) give the illusion of creating available ambient light in a scene. To use the previous examples, a bright outdoor setting requires much more fill light than a dark scene under a streetlamp. Matching color temperature is equally important in the fill light and can be controlled with colored gels. You may opt for several fill lights, silks and or reflectors to achieve the proper lighting of your subject to match the final background plate you’ll be compositing onto.
The Back light is mostly used for studio settings; it creates a soft halo effect on the subject’s hair. This gives a bit more definition from the background but isn’t necessarily good for compositing into a background scene where you need to match lighting. In that case, you should have several fill lights to help provide even lighting.
In any case, be sure your subject is far enough from the green screen and the screen lights so that you have the most control over your foreground lighting and to avoid spill as much as possible.
Another popular, simple setup uses the model lights to light both the screen and the subject. The subject is close to the screen and the Key light is predominantly strong, causing a shadow on the back wall. To compensate for the reflective spill, side spill-suppressor lights on either side of the subject warm up and wash out the spill, creating a clean key in the studio.
This setup is most popular for the purpose of interacting with the back wall surface, such as live TV weather forecasters who make contact with the screen and want to retain shadows on the wall. Directors may sometimes use a blue screen in this case if they want subtle shadows and aren’t worried about reflective spill. Note that your lighting may not be as even in this setup, because you use the available model lights to illuminate both the background and the foreground elements. The side spill lights not only help reduce spill on the subject but can also help even the illumination of the screen if positioned properly.
For more detailed tutorials on lighting options and even low-cost options to build your own light kits, check out my articles Basic Green Screen Lighting Techniques and Simple Green Screen Setups on a Budget in the NewTek Tip Jar.
- Lighting the Subjects
There is a lot of planning you need to consider before lighting your green screen production, and knowing how best to fit your subject into the background when you composite them is one of the first steps.
Most basic green screen shots require a straight-on shot of your subject posed in whatever direction they need to face in order to interact with the intended scene. Your camera is directly opposite the green screen, and the subject is sandwiched somewhere in between, usually facing the camera or perhaps engaging with another subject on-set.
Without changing the lighting of your green screen background, you can easily alter the lighting on your subjects to place them in various environments, simply by keeping them well in front of the green screen (at least 8-10 ft.) and lighting them for the intended scene.
If your subject must come in contact with a background or prop surface, and you need to retain their natural shadows for the composited effect, then you must be especially careful with your green screen setup and lighting to get the right balance of lighting on your subject and the screen itself.
The object is to get the strongest light source on the subject and cast a shadow in the direction you need on to the green screen surface while using smaller fill and rim lights to light only the subject and not the screen if at all possible. I recommend using a stretched fabric such as a Lastolite pop-up screen because there is less chance of bounce-back fill than if you use a painted wall and floor.
For more detailed tutorials on lighting options and even low-cost options to build your own light kits, check out my articles Lighting Your Green Screen Subjects in the NewTek Tip Jar.
- Measuring the Lighting
Regardless what kind of green screen setup you’re using or how you’re lighting it, you need to ensure that your screen is evenly-lit from the camera’s perspective. That means the screen behind your subject is all the same color and brightness. This can be harder than you may think, especially using a pop-up green screen and portable lights. But thankfully, with the advent of portable devices like smartphones and tablets, developers have been busy making useful tools to help you get a fantastic green screen lit, even before you set up your camera.
The Green Screener gives you live feedback on several sensitivity modes; Lo, Me and Hi – which splits up the number of bands of accuracy for each level. If you’re shooting higher definition in a professional studio, then you want to use at least Me/Hi to fine tune your lighting level.
If you’re shooting on a pop-up screen with portable lights, then you only have to light a smaller area behind your subject, it’s easier to define that space by moving your lights around to adjust for it. I’ve found that there’s a big difference between using traditional tungsten “hot lights” and using fluorescents or LEDs, which typically provide more even lighting, especially if they’re dimmable. LED light kits are getting more affordable for small businesses and corporate video departments that need to use them for interviews and product videos.
It’s equally important that what your camera sees is actually measured and adjusted to give you the correct exposure for the green screen keyer to work optimally – and the best way to measure this signal is with a Waveform monitor and Vectorscope. Luckily, the TriCaster has those built in, so you can easily check your exposures and set them during live production.
The two most important scopes you’ll need for green screen are the Waveform monitor and Vectorscope. The Waveform shows you in a horizontal graph what color levels are across the width of the frame. If a level is brighter in one part of the frame it will peak higher in the Waveform than areas in shadow. The Waveform typically displays the level of luminance on a scale of 0 (Black) to 100 (White). This is considered a standard IRE for YC Waveform monitors. You’ll want your Waveform line to be a thin, straight line across the grid around the 65-70 lines. Curves in the Waveform as shown below mean the lighting isn’t even across the screen.
Since you won’t need the TriCaster Scopes on for your entire production, but primarily just for setting up your lighting and adjusting the camera exposure settings, it’s easy to enable the scopes during setup and then return to your desired workspace.
You’ll start by clicking on the Workspace tab from the menu bar and selecting Load Default, which opens a secondary pop-out menu where you can select Scopes down at the bottom as shown below.
Your new Workspace will give you a Preview window of the selected video source (your live green screen camera) on the left, with the Waveform and Vectorscope in the center and the Program window on the right across the top.
Once we replace our talent on her mark, we can see that the green background is still even on both sides in the Waveform monitor and we’ve got a near perfect triangle on the Vectorscope.
Before you return to your regular Workspace mode, you can go ahead and set the LiveKey on your Camera input and adjust to preview your subject against the background in the Program window. You’ll notice that once the video input is keyed, the scopes reflect the absence of the green channel and only show the remaining colors and luminance of the subject in the foreground.
This is why the scopes are so important – you may not be able to see the unevenness of the green screen lighting with your eyes alone, but the scopes don’t lie – and your composites will be much better as a result!
For more detailed tutorials on measuring and scoping your lighting, check out my articles Using Your SmartPhone to Measure Green Screen Lighting and Using the Built-in TriCaster Scopes for Shooting Green Screen in the NewTek Tip Jar.
- Keying the Subject in TriCaster Studio
The TriCaster Studio features a very powerful live keyer, that when you’re compositing a live feed from a camera or using pre-recorded green screen footage, you can get a good matte and mix your subject into the background footage or LiveSet.
Provided you followed all the previous steps for obtaining the best possible green screen imagery to the TriCaster, it’s a simple process of selecting the input channel and applying the LiveMatte tab and selecting the green background near the subject with the eyedropper color selector.
You can make adjustments to the Spill Suppressor and edge smoothness to create the best matte for the composite.
You can crop out unwanted edges of your subject’s channel image, such as stands and the edge of the green screen panel, using the Positioning tab and adjust the Left, Right and Top edges.
Finally, making color correction adjustments may be necessary for your subject, to make them blend in with the background channel. This is most important if your camera wasn’t white balanced the same as the background you’re compositing onto, or if you have multiple camera setups that aren’t set the same or different makes/models of cameras are used.
Portions of this article have been excerpted from The Green Screen Handbook, 2nd Edition (Focal Press, pub.) by Jeff Foster
©2015 Jeff Foster – PixelPainter.com
Learn more about Virtual Sets on TriCaster
More Articles by Jeff Foster:
- Create Sets From iPhone Panoramas and Virtual Set Editor
- Incorporating Your Green Screen Talent Into Virtual Sets
- Simple Green Screen Setups On A Budget
- Lighting Your Green Screen Subjects To Blend With The Intended Background
- Using Your Smart Phone To Measure Green Screen Lighting
- Best Green Screen Materials