Chroma Keying

Keying is the process of isolating a single colour or brightness value in a digital image or moving image and using software to make that value transparent, allowing another image to show through the affected areas.

Luma-keying, is the process of keying out a brightness value or range, like black or white. Chroma-keying identifies a specific colour to remove.

Chroma key involves filming actors and objects in front of a flat screen of a single colour. This screen is usually blue or green, hence chroma key is often referred to as “blue screen” or “green screen” effect.

 

Green Screen Pros:
Results in a cleaner key because digital cameras pick up more information.
Requires less lighting.
High luminance is good for daytime scenes.
Uncommon colour in clothing.

Green Screen Cons:
Colour spill can be too heavy, especially on fine details and edges (or blonde hair)
High luminance is not great for dark or night scenes.

Blue Screen Pros:
Less colour spill is great for subjects with fine details and edges.
Lower luminance is good for dark or night scenes.

Blue Screen Cons:
Requires more lighting.
Common clothing colour, making it difficult to key in post.

Always have the background planned beforehand.
Consider your subject and what they’re wearing.
Light your foreground and your backdrop separately.
Cast broad lighting to avoid shadows and changes to luminosity on the green screen.
Keep the subject at minimum a few feet away from the green screen the further the better.

Make sure you do test shots.
If you are wanting different angles you must consider the background matching up.

The trick is to shoot your subject in away that blends well with the background. In most green screen scenes, the digital backdrops will be a still or clip of video shot form a locked down camera. If the camera moves or shakes, even a little, your subject will appear to bounce around in front of your keyed background scene.

Avoid zooming. TO zoom you will need to track the background to have the zooming qualities (speed and ratio) and dependent on your background you may lose quality.

3 and 5 point lighting:
3 point: Key light, fill light, back light.
5 point: Key light, fill light, back light, 2 extra lights.

Key light: Main light on person
Fill light: Removes some shadow
Back light: Adds extra detail to person