It should be fairly easy to create a Mask (based on Find Edges or High Pass) for two separate applications of the Filter as is, but that’s probably not convenient enough for Your intentions – could You clarify the kind of dialog and settings You are hoping for?
"could You clarify the kind of dialog and settings You are hoping for?"
Having recently done two particularly large slide scanning jobs (over 7000 slides) most of the dust is visible in the sky. There is still dust everywhere else but because people accept that it could be on the buildings / surroundings etc. rather than on the slide then they tend to accept more dust on these parts of the picture. However, the same is not true for the sky which everybody knows it would be impossible for the dust to be present in the sky so it must be on the slide and then they complain. Also, as the sky is lighter than everything else in the picture dust tends to stand out more as it is mostly black.
I would like the filter to assess the picture and if it has a large area consisting of light cyans and whites which are not changing much in colour then it should apply the filter perhaps with a radius of 5 pixels equivalent in the standard dust and scratches filter. If the filter detects lots of changing colours which are not cyan or white then it should step this down to perhaps 1 pixel radius. Obviously the settings could be manually adjusted to allow finite cleaning.
I don't think this would be terribly hard to do as it would really be an adaptation of the traditional dust and scratch filter with an added assessment carried out as to how aggresive the filter should be. I have attached a typical slide which illustrates what I am talking about. There is dust through out the whole picture but it is really apparent in the sky.
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