283.

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to generate local statistics. Figure 1.30 illustrates this idea. In Figure 1.30a, the window is homogeneous and local statistics are calculated using all the pixels within the window, while in Figures 1.30b and c, only those pixels lying in subwindow s2 are used for deriving local statistics.

The RGMAP filter (Nezry et al., 1991) uses a thresholding technique to determine whether the area is homogeneous, and a ratioing operator to decide on the subwindow’s structure (e.g. horizontal, vertical, or slant) over areas considered to be heterogeneous. As a result, the RGMAP filter can simultaneously perform speckle filtering and feature detection (such as detecting edges and linear features). Touzi et al. (1988), Lopes et al. (1990), Nezry et al. (1991), and Baraldi and Parmiggiani (1995) provide more details of the RGMAP filter.

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