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switch variable: $colscale -- funct color scale
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switch value: 12 => color lookup table (real data)

The "lt" (color lookup table) color scale is
designed for user-entered real-valued custom
val->rgb color lookup table.

See right-click help for the "lut:" entry and
buttons to the left (below label line) for more
details on LUT file formats and LUT file flags.

Fade-out Options

By default, this color scale is truncated to
background when the real-valued data is below
$fthresh.  For a smooth fade out, use $fmid,
which sets 50% saturation point.

If a stat has also been loaded (and "mask"
ticked), LUT colors are also truncated to
background when the *stat* is below $sfthresh (or
get faded out using $sfmid, which sets 50%
saturation point).

To make the fade out symmetric around zero
instead of bottom-only (default), set
$zerosymmfadeflag.  To toggle this flag on and
off interactively, click "sym".

To toggle defining colors by their bottom edge
instead of their center (default), click "bot".

To block any truncation or fading of positive
data, toggle $zerosymmfadeflag to 0, unclick
"mask", and set fthresh and fmid to 0.  If the
data and LUT go negative, use a suitably negative
fthresh and fmid.

Complex Phase or Amplitude (vs. def real-valued)

To use a custom color scale to display complex
phase use colorscale "ltw".  To display complex
amplitude, use colorscale "lta".  Click "Col:" to
get a popup with these (and other) color scales.
See right-click help for "ltw" and "lta" buttons
there for details.
