A digital video signal processing system monitors the rate of change of the digital
video signal to detect large rates of change that indicate the presence of an object
edge in the video image. Upon detection of such an edge, the digital signal is
sampled at a variable rate so that more sampling is performed immediately before
and after the sudden change in the signal and less sampling is performed during
the change. The result is that the edge in the video image occupies less pixels
and, therefore, is more clear and defined that would be the case otherwise. Consequently,
the appearance of the video image is enhanced. This can be considered as the digital
analogue of analog H-sweep velocity modulation.
