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tcl funct: mriforce <up,down> -- adj img data targ
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keyboard equivalent: none

The "FAT" button is a convenient way to subtract
1.0 from the current value of $mmid, which
defines the "im:" 3D data value for which there
is no normal 'force' on a moveable surface
vertex.

For a standard 'T1-weighted' scan image (shorter
T1 is brighter), lowering the value of $mmid will
cause a moveable surface near the pial surface
seek a position closer to dark CSF (hence causing
the cortex to get more "FAT").

The "THIN" button adds 1.0 to $mmid, which makes
the moveable surface vertex seek a position
nearer the white matter.
