This invention provides a way of performing improved motion compensated interpolation of moving images, such as television, using motion vectors of variable reliability. By taking into account the reliability of the motion vectors, produced by a separate motion estimation device, a subjectively pleasing interpolation can be produced. This is in contrast to simple motion compensated interpolation, taking no account of motion vector reliability, which is often degraded by objectionable switching artifacts due to unreliable motion vectors. The invention can be used, for example, to improve the performance of motion compensated standards converters used for converting between television standards with different picture rates. The invention allows a gradual transition between motion compensated and non-motion compensated interpolation depending on the reliability of the motion vector used. This is achieved by modifying the temporal interpolation timing, using a look up table, controlled by a vector reliability signal produced by the motion estimator. Effectively this adapts the motion trajectory of the interpolated output pictures.