fScan Reference Manual, Chapter 2 (CmdLineOptions:Expr): Gradient
usage: -expr gradient – create a local intensity gradient map
The GRADIENT function analyzes the local intensity gradient around each voxel and generates a gradient map in which each map value is a composite index of the intensity gradient along the X, Y, and Z axes.
Each map value is a 16-bit integer with 3 5-bit fields, in the binary form: ZZZZZYYYYYXXXXX
Within each field, you should subtract 16 from the 5 bit value (0-31) to get the gradient value (-15 - +15).
The gradient value indicates the average slope of the intensity gradient along that axis.