green screen
what is it?
a 'green screen' is a large Neon green backdrop used as a background which allows for digital effects to be added to the shot during-post production.
This process is also known as chroma keying/chroma key compositing
Compositing = combining two visual elements from operate sources into a single image. this creates an illusion they are all part of the same scene.
why do we use them?
Green screens are used to create a 'plate' which can be edited and layered with special effects/images/cgi later during post production.
this could be adding in a background or even a character. chrome keying technology allows endless possibilities in filmmaking.
you don't have to change the whole background you can green screen a specific section or object.
go behind the scenes on game of thrones to see how important green screen & sfx are
how does it work?
green screen/chroma keying compositing is the technique of layering two images together based on colour hues.
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the subject in front of the green backdrop
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the special effects/image/cgi edited onto the background
solid colour background = matte for your footage
later in post- production you can remove this solid colour background, making it transparent and allowing for compositing.
green vs blue
pros:
Chroma Key Green:
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Most digital cameras capture more information on the green channel. More information = cleaner key around your subject, less noise.
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Green screens also require less light, so they’re great if you’re on a budget.
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The spill from green screens can also make compositing subjects into a daytime scene easier, as green is brighter.
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Most digital keying effects and tools are set up to key out green by default, requiring less fine-tuning for a clean key.
Chroma Key Blue:
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Less colour spill (due to its lower luminance value meaning it reflects less light)
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Great for filming subjects with small details as can retain more information after keying
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Easier to key subjects with blonde hair
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Better for dark or night time scenes
cons:
Chroma Key Green:
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The biggest con of green screens is the amount of colour spill making it difficult to key out fine details like edges and blonde hair.
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High luminance- bad for dark/night scenes. Because the colour green is brighter than blue, it naturally bounces back more light.
Chroma Key Blue:
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Needs more light to properly expose which can be expensive
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Blue can be more common in costumes making it difficult to key.
which one do I use?
blue and green are used for chroma keying as these are the furthest from human skin tones (opposite side of the colour wheel)
green
blue:
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daytime
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colour matching: if there is
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blue in the scene
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nighttime/ dark scene
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colour matching: if there is green in the scene
one is not superior to the other, it is more about the filmmaker choosing the right backdrop for the best outcome
watch this music video to see how they create the moving background:
Music video
Behind the scenes
green screen: the set up
what kit do I need?
hd Digital camera that shoots minimum 24 fps + tripod
green/blue backdrop
lots of lights
green screen: floor plan
Source: Studio binder
Only got two lights? check out the set up below
backlight= creates a separation between subject and background
green screen essentials:
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make sure you set up in an area big enough to perform actions, the actor must keeps within the green screen frame
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the shot needs to be evenly lit using lots of light from various directions, there cannot be any shadows or creases on the green screen backdrop
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avoid wearing green, stripes/ patterns and watches (these can cause issues with keying in post production)
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Place the subject 1.5m away from the backdrop
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keep camera steady using a tripod and sharp in focus
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Take a test shot and practice keying out green screen to see if lighting and shutter speed is good
use soft box lights to help spread the light evenly and reduce harsh shadows
use clamps to hold the green screen in place
top tip:
when checking there are no shadows in your shot use the zebra tool on the camera
Source: Sony
this pattern shows shadow and low light, for a perfect green screen use zebra and position the lights so you cannot see this pattern anywhere in shot
diy green screen:
making a backdrop
green screen suit
painting a backdrop
green screen tips
more media examples using green screen:
find out how to edit using green screen
check out these clips before and after green screen:
