Chromakey apparatus

Claim 2

Chromakey apparatus arranged for mixing a first video signal with a second video signal in accordance with a key signal and including key signal generating means, characterised in that the key signal generating means is adapted to produce a key signal having a magnitude which is determined by a predetermined quadratic relationship with the distance between a reference hue and a hue of said first video signal in U - V chroma signal signal coordinates.

Claim 3

A chromakey apparatus according to claim 1, wherein said means comprises means for supplying input hue point data (U, V) of an input video data signal and a reference hue point data (U 0 , V 0 ), both in U - V chroma signal coordinates; means for producing U - U 0 data and V - V 0 data from said input hue point and reference hue point data; means for converting said U 0 - U 0 and V - v 0 data into (U - U 0 ) 2 and (V - V 0 ) 2 data respectively and adding the same so as to produce an output (U - U 0 )2 + ( V - V 0 )2; means for generating a square root of said data (U - U 0 ) 2 + (V - V 0 ) 2 output; means for converting said data U - U 0 and V - V 0 data into (U - U 0 )cos θ and (V - V O )sin θ data, respectively and adding the same so as to produce (U -V 0 )cos θ + ( V - V 0 )sin θ data , where θ = tan -1 ( ); means for multiplying said data (U - U 0 )cos θ + (V - VO)sin e data by -e (e > 0 ); and means for adding an output of said square root generating means with an output of said multiplying means, whereby an output of said last-mentioned adding means is said magnitude.

Claim 4

A chromakey apparatus according to claim 1 or 2, wherein said means comprises: means for supplying input hue point data (U, V) of an input video data signal and a reference hue point data (U 0 , V 0 ), both in U - V chroma signal coordinates; means for producing U - U 0 and V - V 0 data from said input hue point and reference hue point data; means for converting said U - U 0 and V - V 0 data into -(U - U 0 )sin 6 and (V - V 0 )cos θ data and adding the same so as to produce an output (V - V 0 )cos θ - (U - U 0 )sin 6 where θ = tan -1 ( ); means for converting said U - U 0 and V - V 0 data into (U - U 0 )cos θ and (V - V 0 )sin θ data, respectively and adding the same so as to produce an output (U - U 0 )cos θ + (V - V 0 )sin θ; means for multiplying said output (V - V 0 )cos θ - (U - U 0 )sin 9 by 1/e and then squaring the same; means for squaring said output (U - U 0 )cos θ + (V - V 0 )sin 9 ; means for adding the output data of said multiplying means with the output data of said squaring means; and means for generating a square root on the basis of said added output, whereby an output of said lastmentioned means is said magnitude.

Claim 5

A chromakey apparatus according to claim 1, 2 or 3, wherein said means comprises: means for supplying input hue point data (U, V) of an input video data signal and a reference hue point data (U 0 , V 0 ), both in U - V chroma signal coordinates; means for producing U - U 0 and V - V 0 data from said data; means for converting said U - U 0 and V - V 0 data into data -(U - U 0 )sin 9 and (V - V 0 )cos θ data and adding the same so as to produce an output (V - V 0 )cos θ - ( U - U 0 )sin θ where θ = tan -1 ( ); means for converting said U - U 0 and V - V 0 data into (U - U 0 )cos 9 and (V - V 0 )sin θ data, respectively and adding the same so as to produce an output (U - U 0 )cos θ - (V - V O )sin θ; means for multiplying an output of said first-mentioned converting means, squaring and multiplying the same by n times; means for squaring an output of said second-mentioned converting means: means for adding an output of said multiplying means with an output of said squaring means so as to produce a square root; means for multiplying an output of said second-mentioned converting means by -2 and adding the same with an output of said adding means; and means for multiplying an output of said last-mentioned multiplying means by 1/n, whereby an output of said adding means is said magnitude.

Claim 6

A chromakey apparatus according to claim 1, wherein said quadratic relationship is an ellipse.

Claim 7

A chromakey apparatus according to claim 1, wherein said quadratic relationship is a hyperbola.

Claim 8

A chromakey apparatus according to claim 1, wherein said quadratic relationship is a parabola.

Claim 9

A chromakey apparatus according to claim 1, wherein said quadratic relationship is a circle.

Claim 10

A chromakey apparatus according to any one of the preceding claims wherein the key signal generating means is adapted to produce key signals determined in accordance with a selectable one of a plurality of such quadratic relationships.