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      Converts X, Y position on the image display to the the X,Y position
      on the corresponding image array. (These positions are identical
      only for an unroamed, unzoomed image with with pixel (0,0) of the
      image placed at position (0,0) on the TV.)

Calling Sequence

      UNZoom_XY, Xtv,Ytv,Xim,Yim, [ OFFSET =, ZOOM = ]


      XTV - Scalar or vector giving X position(s) as read on the image
            display (e.g. with CURSOR,XTV,YTV,/DEVICE)
      XTV - Scalar or vector giving Y position(s) on the image display.
      If only 2 parameters are supplied then XTV and YTV will be modfied
      on output to contain the image array coordinates.

Optional Keyword Input

      OFFSET - 2 element vector giving the location of the image pixel (0,0)
              on the window display. OFFSET can be positive (e.g if the
              image is centered in a larger window) or negative (e.g. if the
              only the central region of an image much larger than the window
              is being displayed.
              Default value is [0,0], or no offset.


      XIM,YIM - X and Y coordinates of the image corresponding to the
            cursor position on the TV display.

Common Blocks

      If present, ZOOM_XY will use the TV and IMAGE common blocks which are
      defined in the MOUSSE software system (see
        http://archive.stsci.edu/uit/analysis.html) If the user is not using
      the MOUSSE software (which keeps track of the offset and zoom in each
      window) then the common blocks are ignored.


      The integer value of a pixel is assumed to refer to the *center*
      of a pixel.

Revison History

      Adapted from MOUSSE procedure W. Landsman March 1996
      Converted to IDL V5.0 W. Landsman September 1997
      Proper handling of offset option S. Ott/W. Landsman May 2000
      Put back common blocks for MOUSSE compatibility September 2004

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