Frequency Properties of Two-Dimensional Median Windows - Phase and Amplitude Responses

Janusz Sawicki

Abstract

The use of medians as filtering windows in digital signal processing is known since many years and applied especially when linear filters could not be used, because of specific character of disturbances which are to be removed. This is the case, if, for instance, impulsive disturbances, having very wide spectra, are observed, and linear filters are not suitable for their elimination. Median procedures, including also weighted medians, are particularly effective in such filtering procedures. According to the applied algorithm, disturbed signal samples are eliminated and replaced by some values resulting from neighbouring nondisturbed samples [2]. In spite of the nonlinear character medians can be characterized in the frequency domain if a certain "harmonic linearization" is done. An analysis of such median characteristics in onedimensional case was given in [1, 4]. This idea is now extended to two-dimensional (2D) signals and the frequency properties (amplitude and phase) of the most popular 2D median filtering procedures are examined.

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IMEKO TC

TC4 - Measurement of Electrical Quantities

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