``zero hi voxels'' - zero out bright voxels

VFX name:

iHighZero.

IMPROPTU name:

Zero_hi_voxels.

purpose:

Zero out all voxels greater than a user-preset gray-scale cutoff.

input:

An 8-bit volume.

output:

An 8-bit volume.

parameters:

Default parameters menu is

low_threshold = 0

comments:

1.

A very fast function.