Order filter with progressively decimated filtering window: application to colour image enhancement

The classical definition of vector order filters consists in selecting the pixel that minimizes the cumulated distance to the other pixels of the filtering window. The "most representative" pixel of the filtering window is then selected and the noise is thus reduced. But, when the filtering window reaches a transition, the result is biased and the smoothing is not optimal any more. The proposed technique consists in progressively decimating the filtering window by suppressing the pixels that maximize the cumulated distance. The process is then iterated (computation of the cumulated distances among the remaining pixels and suppression of the less typical pixels) until one single pixel remains. It is then selected for the filter output. In practical cases, the number of iterations is limited. Applied on colour images, the filter results in an enhancement of the edges and in an automatic registration of the different components. The counterpart is a slight degradation of the smoothing performance in homogeneous regions. The paper details the proposed method and compares it with other enhancement filters.