Motion correlation is a way of analyzing movement in image sequences such as television signals. The estimation of movement in television pictures is essential to enable the use of motion compensated processing techniques. These techniques yield improved quality video processing and moving image compression. Motion correlation would be used as part of a video motion estimation system. This invention describes a number of enhancements to, and a simplfied, efficient implementation of, the basic motion correlation algorithm. It is shown how to produce motion correlation surfaces co-timed with output, rather than input, pictures. It is also shown how to average power spectra to obtain improved noise performance, and hence improved accuracy, in motion correlation. Finally it is shown that separate correlation surfaces can be produced relating to `future` and `past` pictures.