Defringe tuning

1) The strength slider was removed because:
- increasing it: does not do much more than as if decreasing threshold
- decreasing it: very similar to using blending or increasing threshold
2) Some parameter tuning and small corner case error corrections.
3) There was also an issue found with the filter radii when using low values, at the same time the artifact filter can now be incorporated in the normal if-condition, reducing code that became redundant by the radius changes