As described in Section
3.1.1, the Magic Wand uses
a search algorithm based on the color of a seed pixel and a specified
threshold value. All contiguous pixels that have color values that
are less than the threshold from the seed are included in the
selection. As already described, the Threshold can be set
interactively. However, it can also be specified in the Magic
Wand's Tool Options dialog.
3.14 illustrates the Threshold
slider which can take values from 0 to 255.