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What is Chroma Keying?
Chroma Keying is the process of creating video or effects by layering two elements together to achieve visual effects, this process is mainly used in video production, Photography and post production.
Chroma colours most commonly used to achieve chroma keying are Blue and Green, the terms blue screening and green screening are used as reference to this process.
The reason for having the option of two colours when chroma keying is to give the creator options when shooting a video.
A scene may require the subject or object to have blue or green colour, If blue jeans were being worn by an actor then a green screen would work fine, but an actor wearing green would need to be recorded using a blue screen.
Blue and Green are considered to be the best colours for chroma keying, it is believed these colour ranges are the furthest from human skin tones allowing a better key when recording a person.
The Chroma Keying Process
Firstly the process of chroma keying is to remove a specific colour from a piece of video footage and replace it with a new element.
This Chroma Keying process is achieved by taking footage of a subject in front of a Blue or Green Screen.
Separate your subject from the backdrop screen by positioning the subject at least 3 feet from the backdrop to get a better key.
Once the footage has been filmed the blue or green colour can be removed from the footage in post production.
Using software that is capable of keying out these colours, such as iMovie makes the green or blue section of the clip effectively becomes transparent.
This process allows the video footage to be layered on top of another video or image, this post production editing changes the appearance of the footage by adding a background element to the film.
Filming Chroma Key Footage
Chroma Key footage is filmed using a blue or green backdrop, the subject is filmed in front of the backdrop.
Obtaining a good key of the subject is important so the footage can be edited easily in post production.
Lighting plays an important role in chroma keying, setting up studio lights correctly helps to achieve a good key.
Light the foreground subject and backdrop separately helps to obtain a good chroma key.
Once the backdrop is in place it is necessary to have an even light across the surface with no hot spots.
Lighting the backdrop should be done first before lighting any subject you are filming.
Natural light as well as Studio lighting can be used to light a backdrop.
Once the backdrop is lit correctly it is then time to light the subject you are going to film.
Normally for good chroma key footage the subject should be at least 3 feet in front of the backdrop, the reason for this is to eliminate any unwanted shadows being cast onto the backdrop.
The subject should not have any colour that matches the colour of the backdrop.
Light the subject from each side, make sure the subject is forward of any lights that are lighting the backdrop.
A light targeted towards the back of the subject can also be used to obtain a good chroma key.
Mount your camera on a tripod and take a test clip and review the footage.
Once you are happy that your subject has a good key, you are ready to start filming.
Chroma Keying Post Production
Post production is the fun part of green screening, this is where you can achieve spectacular results by adding backgrounds or effects to your footage.
To achieve this your footage needs to be edited using video editing software that will allow layers to be added, the video editor must have the capability of chroma keying.
In the video below I will be using iMovie on my Mac Computer, you will be able to achieve the same results with whatever software you decide to use.
Watch the Chroma Keying process to enable you to work easily with your video footage.
Editing Green Screen Footage - iMovie
I hope you found this article Chroma Keying Tips for best results useful, If you would like to leave a comment about your experiences chroma keying your green screen footage please do so below.