NAME:
	ZOOM

 PURPOSE:
	Display part of an image (or graphics) from the current window
	enlarged in another window.

	The cursor is used to mark the center of the zoom.

 CATEGORY:
	Image display.

 CALLING SEQUENCE:
	ZOOM [, FACT = Fact, /INTERP, XSIZE = Xs, YSIZE = Ys, /CONTINUOUS, $
		/KEEP, ZOOM_WINDOW=Zoom_Win, /NEW_WINDOW ]

 INPUTS:
	All input parameters are passed as keywords.

 KEYWORDS:
	FACT:	Zoom factor.  This parameter must be an integer.  The default
		zoom factor is 4.

	INTERP:	Set this keyword to use bilinear interpolation, otherwise
		pixel replication is used.

	XSIZE:	The X size of the zoom window.  The default is 512.

	YSIZE:	The Y size of the zoom window.  The default is 512.

   CONTINUOUS:	Set this keyword to make the zoom window track the mouse
		without requiring the user to press the left mouse button.
		This feature only works well on fast computers.

         KEEP: Keep the zoom window after exiting the procedure.

  ZOOM_WINDOW:	When used with KEEP, returns the index of the zoom window.
		Otherwise, if KEEP is not set, then -1 is returned.

   NEW_WINDOW:	Normally, if ZOOM is called with /KEEP and then called again,
		it will use the same window to display the zoomed image.
		Calling ZOOM with /NEW_WINDOW forces it to create a new window
		for this purpose.

 OUTPUTS:
	No explicit outputs.   A new window is created if necessary. It
	is destroyed upon exit if KEEP is not specified.

 COMMON BLOCKS:
	None.

 SIDE EFFECTS:
	A window is created/destroyed.

	When ZOOM is reusing a zoom window from a previous call to ZOOM,/KEEP,
	then the XSIZE and YSIZE parameters are reset to the actual size of the
	window.

 RESTRICTIONS:
	ZOOM only works with color systems.

 PROCEDURE:
	Straightforward.

 MODIFICATION HISTORY:
	?
       William Thompson, March 1992, added common block ZOOM_WINDOW
		and KEEP keyword.
	William Thompson, 20 May 1993, added ZOOM_WINDOW and NEW_WINDOW
		keywords.

 NAME:
	ZOOM_24

 PURPOSE:
	Display part of a 24-bit color image from the current window
	expanded in another window.  (This procedure was modified from the
	8-bit procedure ZOOM).

	The cursor and left mouse button are used to mark the center of the
	zoom.  The cursor can be moved into the zoom window to determine the
	coordinates (in the original image) and color values of individual
	pixels.  In the zoom window, the right mouse button returns you to the
	mode for selecting a new zoom window or magnification factor
	from the original image.  The center mouse button is used in the
	original picture window to bring up the magnification-factor
	selector.  The mouse button erases the zoom window and pixel window
	and exits.

 CATEGORY:
	Image display.

 CALLING SEQUENCE:
	ZOOM_24 [, XSIZE = Xsize, YSIZE = Ysize, FACT = Fact, /RIGHT]

 INPUTS:
	All input parameters are passed as keywords.

 KEYWORDS:
	XSIZE:	The X size of the zoom window.  The default is 512.

	YSIZE:	The Y size of zoom window.  The default is 512.

	FACT:	The zoom enlargement factor.  The default is 4.

	RIGHT:	Position keyword (0 = left screen, 1 = right screen).

 OUTPUTS:
	No explicit outputs. Two new windows are created, and both
	are destroyed when the procedure is exited.

 COMMON BLOCKS:
	None.

 SIDE EFFECTS:
	Two windows are created/destroyed.  An auxiliary image
	array is created.

 RESTRICTIONS:
	ZOOM_24 only works with 24-bit color systems.

 PROCEDURE:
	Straightforward.

 MODIFICATION HISTORY:
	Original: 9-March-1990	W. T. Vetterling
       Michael Stauffer: 06/23/97 - Add checks for out of range values from
                                    TVRDC on the Macintosh.  Handle !ORDER
                                    properly.