Many factors affect the final result of your composite chroma key. However, by making the right technical and creative choices ahead of time, you can avoid costly mistakes both in time and money! Avoiding these pitfalls can make your key look natural and realistic, unlike what you see typically on your local weather newscasts.
THE BACKGROUND IS AS IMPORTANT AS THE FOREGROUND
Don’t get me wrong, foreground subject is important, but it’s critical you know what background is being keyed in before your shoot. It affects everything you do: the lighting, camera angles, movement, color pallet, etc.
Questions to ask:
- Is it a computerized graphic background or is it a natural scene, interior or exterior?
- What direction does the light come from? For example, if it's an exterior background that is going to be
dropped in post, you don't want to have the subject’s key light on the right side if the sun is coming from the
- Is the background moving or is it static? Is the background evenly lit, 2:1 key to fill ratio or is it a more dramatic, 4:1 or 5:1 ratio? What kind of color tone does the background have? Does it lean towards a bluish look or a warm feel? That way you can gel your lights and white balance your camera appropriately to save time in post. The more information you have ahead of time, the more successful your shoot will be.
THE RIGHT KIT IS KEY
Without the right equipment kit, your key won’t be as clean as it could be and you’ll be spending more time and money in post-production to fix it.
“What camera system, video codec and resolution should you choose”? The old attitude of “oh it’s just for the Internet” doesn’t really fly anymore. The Internet supports up to 4K now and more people are watching Internet video on larger screens.
To avoid a lot of compression artifacting and noise in the picture, the ideal minimum settings you should be recording in are HD 4:2:2 color space and recording codec of 50mb. Recording HD 4:2:0 color space and lower bit rates just creates more problems when keying in post, so just remember: the higher the bitrate, the better the quality of your key.
Recording with a large sensor camera in 4K is a big advantage with even better keying results.
“I’ll just use my small monitor on my camera." You can, but we prefer a large calibrated monitor with a waveform built-in. This is critical in getting your video levels within optimal ranges for your keying software, as well as for any small detail you might miss with a small onboard camera monitor.
“I can get away with any cheap lights, right?" Higher quality, color corrected florescent or LED lighting instruments are recommended. A CRI above 90 is recommended. The cheaper lights can have a green spike in their color spectrum, which is exactly what you don’t want when shooting green screen! However, if you have to use that type of lighting, use a minus green gel to compensate for the color imbalance.
Large soft boxes and diffusion gels will help to get an even distribution of light across your green screen background and a softer look to your subject. These lights produce less heat than tungsten filament lighting and keep the talent cooler. When shooting talent, we prefer shooting daylight balance color temperature (5600 kelvin). 3200K tungsten lighting has a lot of yellow in it and it's closer to the green in the color spectrum.
Tip: We always keep a backup blue screen backdrop with us just in case the talent didn’t get the memo that we are shooting GREEN SCREEN!
The order of what you do is everything.
1. Set up camera and monitor first. Manually set your desired f-stop on camera. f-5.6 is normal as to not have soft focus (short depth of field) when talent moves. To achieve an f-5.6, you may have to add more light depending upon your camera and lens sensitivity. Keying will be better if subject is sharp. You can always create soft edge after the initial key in post.
2. We find it quicker to light the green screen background first with typical small lighting packages. Set up your soft boxes on either side of where talent will be as shown in diagram, and light the background level to 60 IRE on a waveform. This is for optimal illumination for the keying software. If the background is evenly lit, your waveform should be a straight line across at 60 IRE.
3. If you don't have a waveform, set zebras on camera to 60 IRE. Don’t have any lights on except the ones for the green screen background. Using zebras makes it extremely easy to see where your light is uneven! Add or subtract light as needed to see zebra pattern completely across picture, and don’t forget to turn your zebras on your camera back to approximately 70 IRE for flesh tone level.
4. Using green tape, set starting and ending marks for talent - don’t worry about tape marks. The talent can see it and it will key out. Be sure to set marks far enough away as to not create a shadow on the backdrop.
5. Now set key, fill, and backlights for talent. Don’t stress about getting rid of the key light shadow on the floor; a slight shadow on the floor is usually okay, because it will look natural based on your final background that is keyed in. Take special care though if the person is wearing black shoes. This could become a problem trying to key, so make sure those shadows are filled in enough around the feet.
Now, set all your lights for talent and see how it affects your background and floor. Flag or make other lighting adjustments so that your background and floor are evenly lit.
WE’LL FIX IT IN THE MIX
Just because you are a shooter and avoid post like the plague, doesn’t mean you shouldn’t have a working knowledge of post keying software. It behooves you to know what you can and cannot do in post. An example of a good software keyer is Keylight, included within Adobe AfterEffects. We find it a cleaner key with finer adjustments. There are many good ones out there, so I suggest you demo them to see the one you like and fits within your budget.
ALWAYS do a test key on location before you shoot. That way you can make any final lighting and/or wardrobe changes to have a quality shoot. A little time now saves a lot of time later.
NO ONE LIKES A RESHOOT
The details are in the details.
We like to shoot at a higher shutter and frame rate (slow mo, if there is no audio) when shooting fast motion like golf swings, dancing, etc., although shooting at a higher shutter/frame rate requires higher wattage lighting. The higher the shutter and frame rate, the less blur, and the sharper the image of the person or object. A blurred image will look terrible when keyed.
Always have dulling spray on the set along with different colors of tape and gaffer’s tape. For example, when we shoot golf swings, we mask the shaft with matte silver/gray tape to eliminate any green reflections. Anything reflective or silver is not the cameraman's friend. This has to be dealt with on the set... if not, it will be a nightmare in post and you may have to reshoot!
Don’t worry about any grip equipment outside the talents movement. This can be “garbage matted” out. Just as long as the talent doesn’t cross over or behind the grip equipment, you’re fine.
Careful when selecting your talent’s wardrobe. A surprising number of materials are reflective enough to ruin an otherwise perfect key. Jewelry, aluminum or anything highly reflective will catch green and create keying problems, in addition to items like shiny black shoes (these are sure to pick up green reflections) and ‘blue’ jeans where many ‘pre-washed’ styles have faded to reveal a yellow-green tinge create issues. In the general color palette, avoid not only greens, but yellows as well, since many yellow shades contain quite a bit of green. Busy fabric patterns don’t work well either.
YOU’RE NOW A GREENSCREEN GURU
Now relax… you did your homework. Enjoy and have a great shoot! Your competition will be GREEN with envy!
Sorry for the pun, someone had to say it….
Written by Director of Photography | Tom Brunstetter
Tom 's professional experience spans over decades, having worked on national documentaries, commercials, network and cable television series, webisodes, narrative and marketing/sales projects. Flexible, collaborative, sensitive to the clients needs with good people skills - he's a DP who can think outside of the box when needed.
Specialties: Steadicam, 3-axis gimble stabilizers, slow-motion, underwater, helicopter drone cinematography
About Paradise Video & Film
For over 30 years in the South Florida market, Paradise has specialized in providing a core group of highly experienced video camera crews led by DP's who excel in lighting, composition and hand held work. From web content to national programming - we offer a variety of HD camera, sound and lighting packages. Our green screen studio in Fort Lauderdale is pre-lit and measures 20x25 with 2 hard walled cycs. Need production support or specialty equipment? Lighting & grip, mounts & rigging, backdrops, teleprompter, Steadicam, jibs, dollies, DSLR sliders and a variety of camera lenses. We take pride in exceeding our clients’ expectations. For more information, visit: http://www.paradisevideo.com