Search outside values - when set, search is negated - pixels
that would not have been considered within a blob will now be in a blob
and vice versa.
Max is inclusive - when set, search is within min<=v<=max,
otherwise min<=v<max, where v is the pixel
Auto (dark) - see description below
Auto (bright) - see description below
Bimodal - see description below
Position factor - see description below
A threshold is set based on the image's histogram.
- If Bimodal is checked, the histogram should have two
distinct tops (i.e., two major gray levels). A threshold is
calculated assuring maximum separation.
- If Bimodal is not checked, the histogram is assumed not
bimodal. A threshold is still found to separate the image, but since
tops in the histogram are not assumed, the centre of gravity of the
histogram on each side of the threshold is used as a "top" instead.
- The Position factor determines the reported threshold. 0
means the optimum threshold, -1 means the darker top, +1 means the
brighter top. Anything in between leads to linear interpolation
between a top and the threshold.