Toward robust chromatids labelling :

Holed, bended, round shaped chromosomes may lead to poor chromatids labelling with one pair of gray seeds. Here with several pairs of seeds, a much better labelling is reached:

 

Chromatids labelling after watershed

 The result depends on how the seeds were chosen. Four independent factors must be taken into account:

• The pairs of seeds number:
• One pair yields poor results as observed previously.
• The orientation of the pair of seeds  relative to the chromosome
• The axis of the pair of seeds, must be locally orthogonal to the axis of the chromosome.
• For a given pair of seeds, the distance between the two discs.
• The relative orientation of the pair of seeds
• The pair of seeds must have the same orientation

The seeds used to get the result were choosen by hand:

seeds and edge of binary chromosomes in false colors.

When the seeds don't have the same orientation, watershed yields an harlequin  pattern :

Harlequin pattern (black holes are due to the absence of seeds to label the background)