[Almasci] Re: [mmaimcal]Re: Comment in ALMA memo 489

[Mark Holdaway]

>     Mark writes:
> >
> > Long ago, when I was but a child, people used something called "Clean
> > Boxes" to restrict the model brightness distribution.  But now that I am
> > grown, the algorithms have grown up too, and (at least in some
> > packages), you can provide an arbitrary mask image to function as
> > the "clean box".  That mask image can restrict clean components to
> > be within the generalized primary beam pattern for the mosaic.
> >
> >    -M
> >
> >
>     Even I was a child in these days...
> 
>     The arbitrary mask is used in all modern CLEAN tools as far as I know. Yet, it still have the undesirable property
> of sharp edges. It's not an issue if the "clean area" goes beyond the primary beam, but it does not help at all imposing
> more constraints on the large scale shape of the brightness distribution within this area.
> 
>     Perhaps a probabilistic approach (using the primary beam shape as a likelihood indicator on the location of the next
> Clean component) would help. Something similar to simulated annealing could be used in searching for Clean components.
> 
>         Stephane

Perhaps this helps:  in AIPS++, the mask need not be [0|1], but can be
anywhere in between -- so the edge of the PB Mask can be dithered, or, 
whatever it is called when you make the jagged edge of a diagonal line 
look smooth by giving the pixels on the edge some appropriate value
between 0 and 1.  Then again, perhaps I am misunderstanding you
entirely?

   -M

> 
> 
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