Circular thresholding

Most threshold selection algorithms assume that the values (e.g. intensities) lie on a linear scale.

The example shows that the standard linear version of Otsu's method when applied to the hue channel of an image of blood cells fails to correctly segment the large white blood cells (leukocytes).

In contrast the white blood cells are correctly segmented by the circular version of Otsu's method.

There are a relatively small number of circular image threshold selection algorithms.

The following examples are all based on Otsu's method for linear histograms:

Original image: neutrophil white blood cells (leukocytes)
Hue component
Hue component shown as intensity image
Hue component thresholded with linear version of Otsu's algorithm
Hue component thresholded with circular version of Otsu's algorithm