Chroma Key is a special effects for post-production
technique, it involves layering two images, this technique is heavily used to
remove a background from a photo or video and a new background is then added in
replacement. Chroma key can be done with backgrounds of any colour but green
and blue backgrounds are more commonly used because they differ most distinctly
from the human skin colours, to hide a specific part of a person when filming,
you can cover them up with clothes or a blanket the same colour as the
background and when in editing, you take out the background colour and put the
new background in place, therefore removing the part of the body that you want
to remove.
Green is currently
the colour most used for a backdrop as this is colour image that sensors in
digital video cameras are most sensitive to this colour, allowing all the
pixels in the backdrop to be pixelated out, this can produce the clearest
background, bright green has also become the favourite colour for a backdrop as
a blue backdrop might match a subject’s eye colour or clothing such as jeans,
this is how the word “green screen” has come around.
Lighting is the biggest challenge when setting up a
greenscreen, this is because you need to get even lighting and to have an
avoidance of shadows. Materials which are shiny will be far less successful as
they reflect with the background, also a shiny surface will have areas of
reflected light on there, however sometimes a shadow can be used to create a
special effect. Any spill of the chroma key colour will make the end result
look unnatural. You also have to set the lighting up at certain angles and a
certain amount of feet away from the backdrop, there are 3 point lighting which
uses 3 lights or 5 point lighting which uses 5 lights.
As I didn’t know anything about chroma key before this, I
had to find this information out before I started on filming. We set up the
frame, put the backdrop on, set up the lights how we wanted them and put the
camera at the set point that we wanted.
^ This is the best youtube video that I found that helped me learn about Chroma Key
This is the final video from the Chroma Key workshop.
This is about the different backgrounds that we used.
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