1 CLEAN
        CLEAN

    This  task    contains    implementations    of    several    CLEAN-like
    deconvolution  algorithm.  The algorithm is selected through the METHOD$
    keyword, which can be :
     SIMPLE    :  The straightforward direct method.
     CLARK     :  The Barry Clark major-minor cycle method.
     MRC       :  a Multi-Resolution Clean.
     THRESHOLD :  Components are not restricted to be point sources.

    The input map and beam should have the  same  sizes,  except   for   the
    SIMPLE  method where different beam sizes are allowed, and must have the
    same grid spacing.  Sources are searched only in the  inner  quarter  of
    the  map,  but  their  sidelobes are removed in the full map.  A smaller
    search box can be specified if desired.

    The program can process all planes of a data cube at the same time,  but
    a   separate  list  of  component  will be produced for each plane.  The
    cleaning cannot be restarted.
2 METHOD$
        TASK\CHARACTER "Method for Clean" METHOD$

    Specify the algorithm to use among :
     SIMPLE    :  The straightforward direct method.  Safe, but slow.
     CLARK     :  The Barry Clark major-minor cycle method.  Safe and fast.
     MRC       :  a  Multi-Resolution  Clean.   Recommended  for   extended
                  sources or large images.
     THRESHOLD :  Components are not restricted to be  point  sources.   NOT
                  RECOMMENDED, and NOT DEBUGGED.
2 DIRTY$
        TASK\FILE "Input dirty map" DIRTY$

    This is the name of the input "dirty map".  If the map has more than two
    dimensions, all planes will be cleaned successively.
2 BEAM$
        TASK\FILE "Input dirty beam" BEAM$

    This is the name of the input "dirty beam"  (Point  Spread  Function  in
    optical jargon).  The beam can be a cube.
2 RESIDUAL$
        TASK\FILE "Output residual map" RESIDUAL$

    This is the name of the output residual map.  The residual  map  is  not
    deleted at the end of the run.
2 CLEAN$
        TASK\FILE "Output clean map" CLEAN$

    This is the name of the output "clean map".
2 COMPONENT$
        TASK\FILE "Output clean component table" COMPONENT$

    The name of the  table  to  received  Clean  Component  coordinates  and
    values. Default extension is .CCT

2 GAIN$
        TASK\REAL "Loop gain" GAIN$

    This is the gain of the subtraction loop.  It should typically be chosen
    in the range 0.05 and 0.3.  Higher values give faster convergence, while
    lower values give a better restitution of the extended structure.
2 NITER$
        TASK\INTEGER "Maximum number of clean components" NITER$

    This is the maximum number of components  the  program  will  accept  to
    subtract.   Once it has been reached, the program starts the restoration
    phase.
2 FRES$
        TASK\REAL "Maximum value of residual (Fraction of peak)" FRES$

    This is the minimal fraction of the peak flux in the dirty map that  the
    program  will  consider  as  significant.   Alternatively,  an  absolute
    threshold can be specified  using  ARES$.   Once  this  level  has  been
    reached the program stops subtracting, and starts the restoration phase.
    This parameter is normalised to 1 (neither in % nor in db).   It  should
    usually  be  of  the  order  of magnitude of the inverse of the expected
    dynamic range.
2 ARES$
        TASK\REAL "Maximum value of residual (Absolute)" ARES$

    This is the minimal flux in the dirty map that the program will consider
    as  significant.   Alternatively,  the  threshold  can be specified as a
    fraction of the peak flux using FRES$.  Once this level has been reached
    the   program  stops  subtracting,  and starts  the  restoration  phase.
    The unit for this parameter is  the  map  unit.   The  parameter  should
    usually be of the order of magnitude of  the expected noise in the clean
    map.
2 BLC$
        TASK\INTEGER "Bottom left corner of cleaning box" BLC$[4]

    These are the (pixel) coordinates of  the  Bottom  Left  Corner  of  the
    cleaning  box.   Only  the first two coordinates are actually used.  The
    actual cleaning window will be the intersection of the specified  window
    with the inner quarter of the map.
2 TRC$
        TASK\INTEGER "Top right corner of cleaning box" TRC$[4]

    These are the (pixel)  coordinates  of  the  Top  Right  Corner  of  the
    cleaning  box.   Only  the first two coordinates are actually used.  The
    actual cleaning window will be the intersection of the specified  window
    with the inner quarter of the map.
2 POSITIVE$
        TASK\INTEGER "Minimum number of positive components" POSITIVE$

    The minimum number of  positive  components  before  negative  ones  are
    selected.
2 KEEP$
        TASK\LOGICAL "Keep cleaning after convergence" KEEP$

    This is a logical flag to keep cleaning after an approximate convergence
    has been reached.  It should usually be set to .TRUE., except may be for
    the SIMPLE method.
2 MAJOR$
        TASK\REAL "Clean beam major axis" MAJOR$

    This is the major axis  (FWHP)  in  user  coordinates  of  the  gaussian
    restoring beam. If 0, the program will fit a gaussian to the dirty beam.

2 MINOR$
        TASK\REAL "Clean beam minor axis" MINOR$

    This is the minor axis  (FWHP)  in  user  coordinates  of  the  gaussian
    restoring beam.
2 PA$
        TASK\REAL "Position angle of clean beam" PA$

    This  is  the  position   angle   (from   North   towards   East,   i.e.
    anticlockwise)  of  the  major  axis  of the gaussian restoring beam (in
    degrees).
2 BEAM_PATCH$
        TASK\INTEGER "Size of cleaning beam in pixels" BEAMPATCH$[2]

    The dirty beam patch to be used for the minor cycles in  CLARK  and  MRC
    method.  It should be large enough to avoid doing too many major cycles,
    but has practically no influence on the result.   This  size  should  be
    specified  in  pixel  units.  Reasonable values are between N/8 and N/4,
    where N is the number of map pixels in the same dimension.  If set to N,
    the CLARK algorithm becomes identical to the SIMPLE algorithm.
2 CLARK

        A Major-Minor cycles method in which clean components are   selected
    using a limited beam patch, and deconvolved through Fourier transform at
    each major cycle. Usually faster than the Simple Hogbom method.
2 MRC

        A Multi Resolution Clean.  Two maps are cleaned instead of only one:
    a  smooth  dirty map, and the difference between this smooth map and the
    original map.  The same process is applied to  the   dirty   and   clean
    beams.   The  final  clean  map is obtained adding the two clean and two
    residual maps with proper weighting.

    Since the difference map contains no flux,  a  limited  Clean   can   be
    performed  on it.  The smooth map contains only larger structure, and is
    compressed before cleaning.  Deeper clean can be performed  on  extended
    structures,  because they look more point-like and have better signal to
    noise in the smoothed map.  Hence the MRC algorithm is able  to  recover
    more extended structure than a standard Clean.
1 END