Abstract: A chroma keying signal generator has an input (1) to which digitally encoded color difference signals (R-Y and B-Y) are applied and output (27) at which a keying signal is produced. The arrangement calculates a value tan.sup.-1 (R-Y)/(B-Y) which represents the hue and a value (R-Y).sup.2 +(B-Y).sup.2 which represents the (saturation).sup.2. Preselected values of hue and (saturation).sup.2 are stored in latches (20,22) and compared with the calculated values derived from the incoming color difference signals in comparators (24,25). When the calculated hue is substantially equal to the value stored in latch (20) and the calculated (saturation).sup.2 is greater than the value stored in latch (21) both comparators (24,25) produce an output which causes the AND gate (26) to produce a keying signal which is applied to output 27.

Abstract: A method of generating color matte signals includes the steps of: inputting hue, saturation, and luminance values; calculating R, G and B color component values from the hue, saturation and luminance values; calculating luminance (Y), and color difference component (Cr and Cb) values from the calculated R, G and B values; and outputting the calculated Y, Cr, and Cb values. The hue value is in two parts, the first of which defines one of six segments formed by dividing each side of the color triangle in half and the second of which define intermediate values within the segment. The R, G and B values are determined by calculating three color components from the saturation, luminance and the second part of the hue value, and assigning the three color components to registers for holding R, G and B values in dependence on the segment defined by the first of the hue value.

Abstract: A gamma correction factor is applied to a video signal without need of the normally used multiplier by forming the logarithm of the logarithm of the video signal and algebraically adding this signal to a second signal representing the logarithm of the correction factor. The anti-log of the anti-log of the resulting signal constitutes the gamma corrected signal. Analog and digital implementations of the circuitry are illustrated.