Crystal Vision
Chroma Key Tips
10 Chroma Key Tips
Lighting
Proper set lighting is essential for realistic chroma keying and can help to
minimise the amount of time required to set up Safire 3.
The coloured backdrop must be as evenly illuminated as possible over its entire
useable surface. Variations in lighting cause chroma key level variations which
require extra key gain to remove. As key gain is increased, the shape of the key
edges change making the composite result less realistic. Lighting Compensation
controls can help minimise the effects of uneven lighting.
Wherever possible use the same type of lighting on the backdrop – all tungsten,
all LED etc. Try to avoid mixing light types as they have different colour
temperatures and will produce a variable key signal.
The lighting on the backdrop should be diffused and as low level as possible to
minimise spill – that is the reflection of the backdrop colour onto the foreground –
but bright enough to produce a low-noise camera output. Ideally, the backdrop
lighting should have roughly the same incident light level as the subject’s key
light.
Subject Placement
To minimise spill, the foreground subjects should be as far away as possible from
the backdrop, at least 2m. This may not be possible with weather maps, for
example, but some lighting techniques can minimise the effect of spill: up or down
lighting the vulnerable areas with white light can help, as can using a gel of a
complementary colour – i.e. a magenta gel when using a green backdrop.
Background
The backdrop itself should be of a consistent quality: scuff marks, patches etc.
also require increased key gain. Use an internal or external mask signal to force
the composite to BG in difficult areas.
The backdrop should be of a non-reflective nature as should the floor surface. It
is very difficult to avoid keying on foreground reflections from a shiny floor.
Clothing
The colour of foreground objects should be chosen to be dissimilar, wherever
possible, to the backdrop colour. Narrowing the acceptance angle to avoid keying
on foreground objects makes it harder to achieve a good key on variations in
backdrop colour.
Reflective Foreground Objects
Any Foreground object that is reflective may reflect some of the backdrop colour
causing unwanted keying. Use the internal BG mask or external key to prevent
keying on glass table tops etc. unless wanted, but consider that natural
reflections often mirror image the reflected scene.
Safire 3 User Manual R1.3
71
24 March 2017
