pro listfdb, fdb

 Displays TRACE Frame Definition Blocks.
 Calling Sequence: listfdb, fdb
                        where fdb is an (16, n) array containing Frame Definition Blocks.
 CALLED BY
	rdfdb

 NAME:
    LYA_SUBTRACT.PRO

 PURPOSE:
    Given a pair of 1216 + 1600 images, subtract the two with 
    coefficients that follow to produce a "clean" Ly Alpha image.
    Note that this routine does this in two steps:
        (1) Gaussian smooth the 1600 image to reflect the 
            corresponding focus through the 1216 filters, and ...
        (2) Subtract.
 
 CALLING SEQUENCE:
    lya_subtract, index, data, iout, dout, $
                 [,/debug]
 
 INPUTS:
    index, data -- data cube for the pair/triplet of images
          --> NOTE: -->
          The data is expected to meet the following minimum requirements:

          1.  Images are the same size
          2.  Pedestal and dark current subtracted
          3.  Images coaligned OR the /shift keyword set

          The images may come in any order, and any combination
          of two-three UV images will work (though some work 
          better than others).

          Don't normalize the image exposures.

 KEYWORD PARAMETERS:
    shift  -- If set, coalign the image set prior to 
              doing the analysis routine, using TR_GET_DISP.PRO.
    debug  -- Gives small, less-than-useful hints as to what's 
              going on.

 OUTPUTS:
    iout    -- Index structure of output LyA image.
    lya_out -- Computed LyA image, in units of DN.


 CALLS: ***
	TR_GET_DISP [1], TR_GET_DISP [2]
 MODIFICATION HISTORY:
    06-Dec-99 (BNH) - Written