Help for IDP3 BuildMask Widget

The BuildMask Widget is selected from the File Menu in the Main IDP3
Widget.  When activated the widget displays the current reference image.
If no data is loaded into idp3 or the reference image is not ON the
widget will not activate.  If a mask already exists for the reference
image it is loaded into the current mask.  Otherwise, a blank mask of 
all ones to denote good data is created the size of the reference image
upon widget initialization.  Any pixels that are flagged in the display
or mask files that are loaded are combined with the initial mask.  Masked
pixels are shown in the BuildMask Widget display but the Main and ROI
image displays are not affected unless the MaskON button is activated
for that image in the Show Images Widget.

BuildMask Menus:

  File: (mask input/output)
    Load: Activates the Load Mask Widget.  The user may enter a filename
	  with path or Browse for the desired file.
	  The Mask Good Value must be specified in order to interpret the
	  mask.  This value is initially set in the idp3_preferences file.
	  The internal mask always represents 1 as good and 0 as bad but
	  masks may be loaded with any values.  However, only one value
	  in the loaded masks may represent "good pixels".  All other
	  values in the masks are presumed to be bad.
	  The number of good and bad pixels (as determined by the mask
	  good value) may be displayed with the Mask Statistics Button.
	  Multiple masks may be loaded; each with its own mask good value.
	  Each as it is loaded is combined with the current internal mask.
	  The widget closes with the Done button.
    Save: The user may save the current mask with any value to represent
	  both good and bad pixels.  These values are specified in the
	  Output Mask Good and Bad Values.  An output filename may be
	  entered with the desired path or the user may Browse for the
	  appropriate output directory and append the desired name.
	  Hitting Return in the Output File Name Field or selecting the
	  Save Button will cause the mask to be saved to disk as a FITS
	  file and the widget is deactivated.  Cancel closes the widget
	  with no file saved.
  Remove: The user may remove the current mask in memory with Remove.  The
	  internal mask is initialized to all ones (good pixels).  The
	  MaskOn button in the Show Images Widget is deactivated.

  Zoom:   Input images may be zoomed by 1, 2, 4, or 8.  If the resultant
	  output size is greater than the size of the Build Mask Image
	  Display (set in idp3_preferences) the image display is scrolled.

  Edit:   (undo)
    Undo Last Pixel:    The last pixel that was selected to be masked is
		        reset to good.
    Undo Last Freehand: The bad pixels declared in the last freehand region
			are set to good.
    Undo All:           All bad pixels are set to good.

  Display: The image display will show any of the following:
    Data with the Mask ON
    Data with the Mask OFF
    Mask
    Mask with Invalid Pixels (pixels with Invalid value set in idp3_preferences)
    Data with Mask On and Invalid Pixels flagged.

  Blink:  The following sets of data may be blinked.  Each pair is blinked
	  10 times.
    Data with the Mask On then OFF
    Data then Mask

  Done:  Closes the BuildMask Widget

Pixels are marked in the Image Display for masking according to the Mouse
Mode that is selected.  The options are:
  None:  No pixels may be selected but the cursor position (X,Y,Value) is
	 printed in the Display Window.
  Pixel: Clicking any mouse button will cause the pixel under the cursor
	 to be masked.  If the pixel is already masked it will become
	 unmasked.
  Circle: The user will click any mouse button and drag the mouse to the
	  desired circle radius.  The radius is shown and updated in the
	  Circle Radius Field as the mouse is dragged.
  Polygon: Works the same as the polygon function in the ROI.  The user
	  clicks on discrete points with any mouse button to define the
	  line segments of the polygon.  Double clicking on the final
	  point will close the polygon.  All pixels inside of the polygon
	  will be masked.  If the image is zoomed pixels with half or more
	  of its area inside the polygon will be masked.
  Freehand: Uses the Drawpoly procedure written by R.Sterner at the JHU/APL
	  The user may draw any closed shape by first depressing the left
	  mouse button and dragging the mouse to the desired shape, releasing
	  the mouse button and clicking the right mouse button to close.

The image display is controlled by the PlotMin and PlotMax values specified
in the Widget.