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Chromakeying, the TV trick in which actors perform in front of a blue
background which is electronically blanked out and replaced by a fake backdrop,
has a big disadvantage: studio lighting must be very bright to trigger the
blanking electronics. To get round this, the BBC proposes that the actor stands
in front of a black material coated with reflective glass beads (GB 2 321 814).
The camera lens is surrounded by a ring of coloured LEDs. The light from them
hits the beads and bounces back to the camera. The reflected light, which is too
weak to colour the actors, is very pure in frequency and so can be blanked out
easily—so no powerful studio lighting is necessary.