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tickbox variable: $botedgelutflag -- for real color LUT
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default: 0 (FALSE)

If the "bot" tickbox (upper right) is ticked, the
r,g,b entries in the user-defined color lookup
table (e.g., in $iscandir/scripts/*.lut) specify
the bottom of the color range for each given val.

If not ticked, each color in the color LUT define
the center of the color range.


See "intp" tick to control whether colors in
between val table entries are interpolated or
constant, and "sym" tick to determine whether
(s)fthresh and (s)fmid cut into color scale from
the bottom or symmetrically in both directions
from zero.

See help for "lut:" entry for more details.

N.B.: no effect of tick on phase LUT (always ON,
i.e., always interpolated).
