FILTERING OF DIGITAL VIDEO SIGNALS

摘要

The present invention concerns the filtering of digital video signals and has particular application to filtering noise from such signals. This makes the signals easier to compress. According to the invention, the video signals are subjected to a filtering process in which the signals are multiplied by a first variable gain coefficient. A delayed sample of the signals is derived by a delay circuit and the delayed sample is multiplied by a second variable gain coefficient. The two multiplied signals are added together. The magnitudes of the first and second gain coefficients are varied in dependence upon a comparison between the input video signal relative to the delayed sample from the delay circuit. The magnitudes of the two gain coefficients are varied in the opposite sense to one another. By a suitable choice of the gain coefficients, the filtering process can be used to preserve the sharpness of large transitions in picture information and the impulse response of the filter can be readily modified by recalculating the gain coefficients. The filtering process may be used in a cascade of stages to achieve filtering in the two spatial domains and in a temporal domain.