A region will be considered inconsistent if the percentage
of its inconsistent pixels exceeds a certain proportion s.
The standard deviation to the fitted line is computed.
The noise variance is estimated locally for each pixel.
If it is farther from the fitted line than a certain factor
times the standard deviation, the pixel is marked as inconsistent. Pixels for which the noise is too strong are
made white, those for which it is too weak are made
black. When a region contains too high a proportion of
white or black pixels it is itself marked as inconsistent
and made white or black accordingly.