The histogram in Fig. 8.24b has a small peak in the white region due to the
anhydrous phase. The threshold value is automatically determined with the 1-D
watershed technique. This is done by computing the one-dimensional watershed
on the filtered, negated histogram. The filter is based on a closing of 5 points
followed by an h-minima operation with h ¼ 10 (see Fig. 8.24c). The threshold
parameter is taken as the position of the watershed point.
Anhydrous regions are detected by applying the automatic threshold and by
removing objects with area less than 20 pixels. Their contour, computed from
the gradient, is overlaid (in black) on the input image in Fig. 8.24d. Figure 8.24e
shows the watershed applied on the filtered gradient of the input image.
The