Improvements in or relating to video image keying systems and methods

DETAILED DESCRIPTION The object of the present invention is to reduce the problem of spurious signals such as illustrated above.
According to one aspect of the present invention there is provided an image processing system in which first image data, representing at least one foreground image keyed to a portion of a first background in accordance with respective keying data, is combined with second image data, representing a second background, to produce data defining a combined image comprising said at least one foreground image keyed to a portion of said second background, the system being arranged such that the second image data is weighted by control data derived from said keying data before being combined with the first image data such that data representing the first background is replaced by the second image data.
According to another aspect of the invention there is provided a keying system for television image processing, the system comprising: a source of first video signals V representing a foreground object F keyed over a first background B; a source of second video signals representing an arbitrary background Bg; a source of key signals (.
alpha.
) for keying the foreground object over the arbitrary background Bg; and a keying circuit responsive to said first and second video signals and said key signals to produce the result R=V+Bg(1-.
alpha.
).
On the condition that: V=FK+B(1-K) as above (1) B=0; and .
alpha.
=K, (2) the above result R is: R=FK+Bg(1-K) which yields the required blend for soft edging between the foreground and the arbitrary background, Bg, with no contribution in the Result from the background B.
That is to say, the first background B is replaced by the new arbitrary background Bg in such a way as to avoid the introduction of spurious artifacts such as halos or shadows in the resultant image.
According to another aspect of the invention there is provided an image processing system comprising a first data source for supplying first image data representing a first image formed from at least one foreground image keyed to a first background image by interpolation in accordance with at least one respective first interpolation coefficient and for supplying a second interpolation coefficient derived from the or each first interpolation coefficient, and a divider for dividing the first image data by the second interpolation coefficient