KEYWORD
     PolygonData ZWT CreateMode Area Threshold TrimOutput Rolloff

DESCRIPTION : CutMask
     Cut Mask takes an existing image data set and masks out
     regions to generate a new data set.  The regions masked
     out are controlled by a threshold and a polygon list
     created with Edit Polygon, 2D Object Finder, or FPPolygons.
     The masking can be done in one of two ways:

     1) A binary mask is generated where the regions to be
        masked out are set to zero and the rest is set to one.
        Use the "Mask" mode option to get this behavior.

     2) The regions to be masked out are set to the first
        wavelength's minimum data value and the rest is
        unmodified.  Use the "Data" mode option to get this
        behavior.

PolygonData
     To specify the polygon data to be used, you must first
     specify the data set to be masked by either pressing
     the "Image file" button to open a file selection dialog
     or directly entering into the adjacent field the window
     number or file name.  If the image data is from a window,
     Cut Mask will detect if there are polygons loaded already
     and use those by default.  If the input is from a file
     or if a different set of polygons is desired for a
     window, select the polygon list file by pressing the
     "Polygon data" button to open a file selection dialog
     or enter the file name directly in the adjacent field.

     When a new polygon list is chosen and there is already
     polygons loaded, you will be prompted whether the new
     polygons should be appended to the current list or should
     replace the current list.

ZWT
     Use the "Z", "W", "T" controls to restrict the range of
     z sections, time points, and wavelengths that are processed
     from the source data set.  For z and time, the range is
     specified by three values: the starting index, the final
     index, and an increment.  For the wavelengths, there is
     a toggle button per wavelength, and if the toggle is on,
     the wavelength will be processed.

     When an input data set is selected, the z and time ranges
     and the wavelength toggles are updated to cover the entire
     data set.  As a shortcut to restore the controls to
     settings that cover the entire input data set, press the
     "set all" button.

CreateMode
     Use the "Mode" option menu to control how the input data
     is masked to generate the output.  There are two available
     options:

     Mask  Points in the input which are to be masked out
           (based on the polygon list, area setting, and
           threshold) are set to zero.  Points in the input
           which are not masked out are set to one if the
           input data set is real-valued or 1 + i if the
           input data set is complex-valued.

     Data  Points in the input which are to be masked out
           are set to the first wavelength's minimum data
           value if the input data set is real-valued (the
           minimum is read from the header of the input data
           set and is not recalculated) or zero if the input
           data set is complex-valued.  For points which are
           masked out, the value from the input data set is
           preserved.

     If the rolloff option is enabled, points in the masked
     out region near an masked-unmasked boundary will have
     their values modified; consult the description of the
     rolloff option for details.

Area
     If the "Area" option is set to "Inside", the masked out
     points are those which are outside any of the polygons
     in the polygon list or those which are inside one or more
     of the polygons but which have intensity levels below the
     intensity threshold.  If the "Area" option is set to
     "Outside", the masked out points are those which are
     inside one or more of the polygons and which have intensity
     values greater than or equal to the intensity threshold.

Threshold
     If the input data set is real-valued, a point falling
     inside a polygon in the polygon list will have its value
     compared to the threshold level to determine whether the
     point is to be masked out or not (see the description of
     the area option for details).  For complex-valued data,
     the threshold is ignored and the polygon list is the only
     factor that determines whether or not a point is masked out.

     When a new input data set is chosen, the threshold is
     reset to the minimum data value for the first wavelength,
     as recorded in the header of the input data set.

TrimOutput
     If the "cut small" toggle is not on, the generated data
     set has the same x and y dimensions as the input data set.
     If the toggle is on, the x and y dimensions are set to be
     the smallest such that all polygons in the polygon list
     are enclosed.

Rolloff
     If the "rolloff" toggle is on, the values at masked out
     points near a masked-unmasked boundary are modified to
     smooth the variation in intensity between unmasked and
     masked regions.  The smoothing is performed as follows:

     1) Given a masked out point, compute the distance, d, from
        the nearest unmasked point in the same section.

     2) If d is less than 5 pixels, the value at the masked
        out point is changed to

             o + d / 5 * (m - o)

        If the "Mask" mode option is used, o is one if the
        input data is real-valued or 1 + i if the input data
        is complex-valued, and m is zero. If the "Data" mode
        option is used, o is the value at the point in the
        input data set and m is the value used for masked out
        points (the first wavelength minimum value for real-
        valued data and zero for complex-valued data).