Real-time median-window filtering of video signals

Abstract. Several hardware methods for selecting the median value of a set of input signals are described. Two of the systems are based on the use of an analog multiplexer to select the channel containing the median value. The input levels are pairwise compared with comparators, and the comparator outputs provide logic levels to drive the address lines of a multiplexer. A third method involves the use of saturable amplifiers and a summing junction. An interesting feature of this system is that it can act as a median filter, a linear averaging filter, or a combination of the two. A circuit whose output automatically hunts around the median value is described next, and the final circuit relies on diode switching networks in the feedback loop of operational amplifiers to select the median input. Schematic circuits are provided.