Function otsu_threshold 

pub fn otsu_threshold(data: &[f64], num_bins: usize) -> f64

Otsu’s method for automatic threshold selection

Finds the threshold that maximizes inter-class variance over a histogram spanning the data’s own range (all values, zeros included), and returns the threshold at a bin edge. For MATLAB’s graythresh on double data, which does not rescale, see [graythresh].

Arguments

• data - Input data (e.g. flattened 3D image)
• num_bins - Number of histogram bins (typically 256)

Returns

The optimal threshold value