NAME

       mDiff - Calculates the difference between a pair of overlapping images

SYNOPSIS

       mDiff [-d level] [-n(o-areas)] [-s statusfile] in1.fits in2.fits out.fits template.hdr

DESCRIPTION

       mDiff  calculates a simple difference between a single pair of overlapping images. This is
       meant for use on reprojected images where  the  pixels  already  line  up  exactly.  mDiff
       analyzes an image metadata table to determine a list of overlapping images.  Each image is
       compared with every other image to determine all  overlapping  image  pairs.   A  pair  of
       images  are  deemed to overlap if any pixel around the perimeter of one image falls within
       the boundary of the other image.

OPTIONS

       -d level
              Turns on debugging to the specified level (1-4).

       -n     No-area-images flag. Creates difference image without  requiring  pixel  area  FITS
              image

       -z factor
              Scale second image by factor before subtracting.

       -s statusfile
              Output and errors are sent to statusfile instead of to stdout

ARGUMENTS

       in1.fits
              First input FITS file.  (Also needs area image in1_area.fits, or use -n flag)

       in2.fits
              Second input FITS file.(Also needs area image in2_area.fits, or use -n flag)

       out.fits
              Difference FITS image to be generated.

       template.hdr
              FITS header template used to generate output image.

RESULT

       FITS image and area image representing the difference in the overlap region.

MESSAGES

       OK     [struct stat="OK"]

       ERROR  Cannot open status file: statusfile

       ERROR  Images don't overlap

       ERROR  All pixels are blank

       ERROR  Template file not found

       ERROR  FITS library error

       ERROR  general error

EXAMPLES

       $ mDiff proj/in1.fits proj/in2.fits output/diff.fits template.hdr
              [struct stat="OK"]

BUGS

       The drizzle algorithm has been implemented but has not been tested in this release.

       If  a  header  template  contains  carriage  returns  (i.e., created/modified on a Windows
       machine), the cfitsio library will be unable to read it properly, resulting in the  error:
       [struct stat="ERROR", status=207, msg="illegal character in keyword"]

       It  is  best  for the background correction algorithms if the area described in the header
       template completely encloses all of the input images in their entirety. If parts of  input
       images  are  "chopped  off"  by  the  header  template,  the background correction will be
       affected. We recommend you use an expanded header  for  the  reprojection  and  background
       modeling  steps, returning to the originally desired header size for the final coaddition.
       The default background matching assumes that there are no non-linear background variations
       in  the  individual  images  (and  therefore  in the overlap differences). If there is any
       uncertainty in this regard, it is safer to turn on the "level  only"  background  matching
       (the "-l" flag in mBgModel.

COPYRIGHT

       2001-2015 California Institute of Technology, Pasadena, California

       If  your  research  uses  Montage,  please  include  the  following acknowledgement: "This
       research made use of Montage. It is funded by the National Science Foundation under  Grant
       Number  ACI-1440620,  and  was  previously  funded  by  the National Aeronautics and Space
       Administration's Earth Science Technology Office, Computation Technologies Project,  under
       Cooperative  Agreement  Number  NCC5-626  between  NASA  and  the  California Institute of
       Technology."

       The Montage distribution includes an adaptation of the MOPEX algorithm  developed  at  the
       Spitzer Science Center.