Green screen video involves filming your subject in front of a green background, usually fabric or painted, with the intention of removing the background during post-production video editing.
This allows you to use an alternative background for your shot, this could be a photograph or digital image, video footage shot elsewhere or computer generated imagery.
In your video editing software you will use an editing effect called 'chroma keying' to remove the green background from your shot and a process called 'compositing' to layer your footage together with your choice of background.
Chroma keying doesn't just work on backgrounds, it can also be used for props, characters, costumes or set elements. This is achieved by wrapping or painting these elements in the same bright green as would be used for the background. The editing of these elements can often be more complex.
Green is not the only colour which can be keyed out during video editing, any solid monochromatic screen could be used for keying. The reason bright green is used most frequently is that it's the least likely colour to be found in the skin, hair and clothing of human subjects.
Bright blue is another colour used in the film industry where green is unsuitable, such as where costume or prop elements contain green.
Green screen allows you to transport your subject into an alternative environment which you might not have access to, or into an imaginative creative environment. As a filmmaking tool it is expanding our ability to portray fantastical worlds. As a practical tool it can facilitate neat professional environments at a low budget.
At a basic level, green screen can be used effectively in creative music videos, works for children, comedic works, presentations, instructional videos and video communication. In these contexts it is not always necessary for us to believe the subjects are really in the environments they're presented in.
At a professional level, green screen is used in television, feature films, creative video work and music videos to believably transport artists into environments. In these contexts we want to believe the artists or characters are living in these worlds, we don't want to notice any technical issues and attention to details is integral.
Green screen is on the face of it a simple process that requires a deceptive level of digital competency.
This is not to dissuade those who would like to try it out, but to understand that getting to grips with it may take a bit of practice and learning some new skills.
Light your green screen - Your green screen should ideally have its own light source and be lit as evenly as possible. Shadows and uneven colour can make your keying process more challenging.
Make sure your green screen is flat - Ensure your green screen is as flat as possible, this can be done by pulling the fabric tightly and securing it with clips, or by ironing or steaming it. Again, this is to ensure minimal shadows and creases which can make your editing process more challenging.
Avoid green, light coloured or reflective clothing - You don't want there to be any green present in your subject. Green clothing should be self explanitory, but light coloured or reflective fabric could also reflect the green colour and result in the visual presence of green on your subject. If your subject has any green present, these elements will also be removed during the keying and can result in 'holes' appearing in your subject.
Keep hair as neat as possible - Keying out hair elements can be challenging depending on the colour or hair, lighting, etc. Keeping hair as neat as possible will give you the best shot at a clean key effect.
Light your subject - Lighting your subject should aim to replicate the lighting of your chosen background as closely as possible in colour, direction and brightness. If your background scene is outdoors, one of the best things to do would be to bring your green screen outdoors and film in as similar lighting conditions as possible. This is one of the things which can really separate your subject from your background if not achieved. If your concept does not rely on realism then light for creative effect.
Keep distance between your subject and screen - Your subject should ideally not be positioned close to your green screen as this will create shadows on your green screen. Shadows result in a background consisting of different shades of green and can make keying harder. Being close to the screen can also increase the possibility of colour spill where the green colour shines onto your subject.
Record at 50 or 60fps - Shooting at a higher frame rate by default will give you a faster shutter speed. This minimises the effect of motion blur which software can struggle with interpreting.
Record in high quality setting - Not all smartphones will be capible of pro-res recording settings, but where available these higher quality settings will assist with your editing process.
The link below contains a selection of copyright video files from Pixabay which can be used to try out green screen editing in your chosen software.
The link contains a combination of well lit shots and others with background variations and shadows to show you the difference in editing each.
Green screen shots are often very static due to the technical limitations of the green screen set up and background elements.
When green screen is combined with animation software such as Unreal Engine and Blender in the hands of a skilled editor, the results can be unbelievable and really elevate the immersive quality of the videos created.
These types of set ups and and editing require a huge amount of technical proficiency and time to achieve.