Method of inserting a background picture signal into parts of a foreground picture signal, and arrangement for performing said method

An arrangement for inserting a background picture signal into key color-characterized parts of a foreground picture signal, in which fading operations are performed between the picture signals in transition regions in dependence upon a control signal (k), while intermediate colors occurring in the transition regions in the foreground picture signal are transformed into new intermediate colors which constitute a transition from the color of the foreground picture signal to that of the background picture signal, the control signal (k) having a first value in the region of the key color and reaching a second value at transition boundaries, the transition boundaries in a C.sub.b /C.sub.r color plane being constituted by two straight lines of origin, each of which representing a selectivity and each enclosing an angle (.alpha..sub.L and .alpha..sub.R) with the vector of the key color, wherein the straight lines of origin representing the selectivity (SEL.sub.L and SEL.sub.R) are differently adjustable within a frame period by changing the angles (.alpha..sub.L and .alpha..sub.R), characterized in that said arrangement comprises:

• a coordinate transformation circuit having an input for receiving the color signals (C.sub.b, C.sub.r) and outputs for supplying transformed coordinate signals (R, S), with the color location of the key color (KC) being on the R axis;
• a first multiplier having a first input for receiving one of said transformed coordinate signals (S) from the coordinate transformation circuit, a second input for receiving a negative tangential value of an angle (W), and an output for supplying a product signal;
• an adder having a first input for receiving the other of said transformed coordinate signals (R) from the coordinate transformation circuit, a second input for receiving the product signal from the first multiplier, and an output for supplying a sum signal;
• and
• a second multiplier having a first input for receiving the sum signal from the adder, a second input for receiving a reciprocal value of the key color vector (D.sub.KC), and an output for supplying the control signal (k).