Abstract: A motion predictive inter frame compression system comprising a wavelet transform unit (80) for transforming space domain image data to the frequency domain. A motion estimator (30) operates in the space domain to produce motion vectors. The motion vectors are converted in a converter (31) to the frequency domain.

Abstract: A method of generating an output array of image spatial frequency coefficients from input arrays of image spatial frequency coefficients overlapped by the required array, the spatial frequency coefficients being transformable to image pixel values by a predetermined spatial frequency transformation, comprises the steps of: matrix-multiplying each input array by one or more respective matrices having coefficients derivable by applying the inverse of the predetermined spatial frequency transformation to respective translation matrices which, if matrix-multiplied by that input array, would provide a translation of the overlapped portion of that input array to an overlapping position in the output array; and matrix-adding the respective matrix products generated from each overlapped input array.

Abstract: Video down-conversion apparatus in which lines of successive output video field are interpolated from lines of respective input video fields, the apparatus being selectively operable to interpolate each output field from an input field of either field polarity so that the successive output video fields can maintain a regular odd-even field polarity sequence even if there is a discontinuity in the field polarity sequence of the input video fields.

Abstract: In deriving a key signal for a digital mixer from an input video signal, most values of the key signal are derived by a clip and gain circuit. However, in the special case where the normalized product values for adjacent pixels lie on opposite sides of the upper and lower bounds, the following equations are used to determine the key values (K.sub.i and K.sub.h) for the two adjacent pixels:K.sub.i =0.5 (Ub-Lb)*[P.sub.b -0.5 (Ub-Lb)]/(P.sub.h -P.sub.i),K.sub.h =K.sub.i +0.5 (Ub-Lb),where Ub and Lb are the upper and lower bound values respectively, and P.sub.i and P.sub.h are respectively the lower and higher product values of said two adjacent pixels.