KEYWORD
    Atan Fraction MinMax

DESCRIPTION Edge
    Edge Enhancement uses the image intensity gradient to
    enhance object boundaries.  At any pixel, i, the
    result at that pixel is given by

         result(i) = input(i) * (fraction + (1 - fraction) *
              gradient(F(input))(i))

    where fraction is a number between 0 and 1 and F is
    either a linear or an arctangent function.


    Edge Enhancement accepts the command-line arguments
    described in Region.hlp.  In addition, Edge Enhancement
    has the following options (optional parts are shown in
    brackets):

         -atan
              If present on the command line, this option causes
              the arctangent of the input data (after clamping
              to the range given by the minimum and maximum
              values) to be used.  The default is to use the
              clamped input data without further modification.

         -fraction=weight
              Sets the weighting factor for combining the gradient
              of the input data and the input data.  Valid values
              for weight are between zero and one with larger
              values giving a result that is closer to the input
              data.

         -scl1=min[:max]
              Sets the minimum and maximum used to clamp the
              first wavelength's data before calculating the
              gradient.  The default is to use the minimum
              and maximum values recorded in the input's header.
              There are similar options (-scl2, -scl3, -scl4,
              and -scl5 to set the range for values drawn from
              other input wavelengths).

     As an example, the following writes the gradient amplitude
     to gradient.dat for every other of the first thirty time
     points in series.dat; the arctangent is taken before
     computing the gradient:

          Edge series.dat gradient.dat -atan -t=0:29:2

Atan
    When this toggle is on, the arctangent of the input (after
    scaling it with the given minimum and maximum values).
    When the toggle is off, the input is simply restricted
    by the minimum and maximum values.

    In some cases, applying the arctangent function gives
    improved edge enhancement.

Fraction
    This is a weighting factor between zero and one which
    determines the relative contributions of the original
    image and the gradient of the original.  With a larger
    weighting factor, the result of the edge enhancement will
    look more like the input image.

MinMax
    In the gradient calculation, the input image values are
    restricted to fall in the given range.  Values outside the
    range are taken to be the value of the closest endpoint.