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.

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.

Erode Regions

Invalidates pixels on
the edge of groups of pixels. The number of pixels to erode along the edge is
specified.