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WFPC-2 Shutter Shading Correction --- Edward Ajhar 4/29/93
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The files to correct for shutter shading are as follows:

pc1adt.fits: delta_t(x,y) file for PC1 images with 
              E_BLADEA= 'CLOSED' in the header file
pc1bdt.fits: delta_t(x,y) file for PC1 images with
              E_BLADEB= 'CLOSED' in the header file
wf2adt.fits \
wf2bdt.fits  \
wf3adt.fits   \___  similarly for the WF's
wf3bdt.fits   /
wf4adt.fits  /
wf4bdt.fits /

These files are in 32-bit floating point FITS format and should be
readable like IRAF floating point FITS images.  The images are 798x798
with (0,0) as the origin and assume that WFPC-2 images also have (0,0)
origin.  (In other words, no correction is given for the last two
columns or the last two rows.)  The pixels are in units of seconds,
and the images should be applied as follows:

For some image where c(x,y) represents the counts in the pixel at
(x,y) and whose exposure time is t_exp, the corrected count


                             c(x,y) 
	c'(x,y)  =  --------------------------   ,
                     1 + delta_t(x,y) / t_exp


where delta_t(x,y) is from the appropriate image from the above list.

The correction is small for most exposures since delta_t(x,y) is
around a couple of milliseconds.