Basic Information on clean

Task: clean
Purpose: Apply Hogbom, Clark or Steer CLEAN algorithm to a map
Categories: deconvolution

        CLEAN is a MIRIAD task that performs a hybrid Hogbom/Clark/Steer
        Clean algorithm, which takes a dirty map and beam, and produces
        an output map which consists of the Clean components.  This
        output can be input to SELFCAL to self-calibrate visibilities,
        or input to RESTOR to produce a "clean" image.  Optionally CLEAN
        can take as one of its inputs a model of the deconvolved image.
        This model could be from a previous CLEAN run, or from other
        deconvolution tasks (e.g. MAXEN).

Key: map
        The input dirty map, which should have units of Jy/beam. No
        default.

Key: beam
        The input dirty beam. No default

Key: model
        An initial model of the deconvolved image. This could be the
        output from a previous run of CLEAN, or the output of any of the
        deconvolution tasks (e.g. MAXEN). It must have flux units of
        Jy/pixel. The default is no model (i.e. a zero map).

Key: out
        The name of the output map. The units of the output will be
        Jy/pixel.  This file will contain the contribution of the input
        model.  It also should have a different name to the input model
        (if any).  It can be input to RESTOR, CLEAN (as a model, to do
        more cleaning), or SELFCAL (for self-calibrating visibility
        data).

Key: gain
        The minor iteration loop gain. Default is 0.1.

Key: options
        Extra processing options. Several can be given, separated
        by commas. Minimum match is used. Possible values are:
          negstop   Stop when the first negative component is
                    encounterd.  This does not apply when using Steer
                    iterations.
          positive  Apply a positivity constraint.  This constrains the
                    component image to be non-negative.  A side-effect
                    of this is that CLEAN will stop iterating if it
                    cannot continue to ensure this.  This does not apply
                    when using Steer iterations.
          asym      The beam is asymmetric.  By default CLEAN assumes
                    the beam has a 180 degree rotation symmetry, which
                    is the norm for beams in radio-astronomy.
          pad       Double the beam size by padding it with zeros. This
                    will give you better stability with Clark and Steer
                    modes if you are daring enough to CLEAN an area more
                    than half the size (in each dimension) of the dirty
                    beam.

Key: cutoff
        CLEAN finishes either when the absolute maximum residual falls
        below CUTOFF, or when the criteria described below is
        satisfied. The default CUTOFF is 0.
        When two values are given, do a deep clean to the second cutoff
        limiting peak finding to the pixels that are already in the
        model.

Key: niters
        The maximum number of minor iterations.  The default is 250,
        which is too small for all but the simplest of images.  CLEAN
        will stop when either the maximum number of iterations is
        performed, or the cutoff (see above) is reached, or if
        options=negstop was given and a negative component was found,
        or if options=positive was given, and no more positive
        components could be found. An optional second
        value will force CLEAN to report on the level reached and
        (for mode=clark) start a new major iteration at least every
        niters(2) iterations. This can be useful to avoid overcleaning.

Key: region
        This specifies the region to be Cleaned.  See the help on
        region for more information.  The default is the largest
        region that can be deconvolved safely.

Key: phat
        Cornwell's Prussian helmet parameter.  When cleaning extended
        sources, CLEAN may produce a badly corrugated image.  This can
        be suppressed to some extent by cleaning with a dirty beam which
        has had a spike added at its center (i.e. a beam that looks like
        a Prussian helmet).  PHAT gives the value of this spike, with 0
        to 0.5 being good values.  Default is 0 (but use a non-zero
        value for extended sources).

Key: minpatch
        The minimum patch size when performing minor iterations, in
        pixels.  Default is 51, but make this larger if you are having
        problems with corrugations.  You can make it smaller when
        cleaning images which consist of a pretty good dirty beam.

Key: speed
        This is the same as the speed-up factor in the AIPS APCLN.
        Negative values makes the rule used to end a major iteration
        more conservative.  This causes fewer components to be found
        during a major iteration, and so should improve the quality of
        the Clean algorithm.  Usually this will not be needed unless you
        are having problems with corrugations.  A positive value can be
        useful when cleaning simple point-like sources.  Default is 0.

Key: mode
        This can be either "hogbom", "clark", "steer" or "any", and
        determines the Clean algorithm used. If the mode is "any", then
        CLEAN determines which is the best algorithm to use. The default
        is "any".

Key: clip
        This sets the relative clip level in Steer mode. Values are
        typically 0.75 to 0.9. The default is image dependent.
 
Revision: 1.17, 2019/02/09 06:59:27 UTC