Erosion reduces the number of valid pixels based on specified criteria. This is normally used to reduce noisy pixels. Erosion can be accessed using the Modify | Pixels | Point | Erode menu item.
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Invalidates pixels whose height is outside a specified range. The range is specified as symmetric about the mean height value. The symmetric limit is specified in units of standard deviations (sigma) of the surface height distribution. The surface height histogram can be plotted using Analysis | Statistics | Histogram. See Statistics. The highlighted areas of the histogram below represent the pixels that would be invalidated if +/- 1 sigma was specified as the rejection limits.
Invalidates pixels on the edge of groups of pixels. The number of pixels to erode along the edge is specified.