Function label_histogram 

pub fn label_histogram<S>(
    labels: &ArrayBase<S, Ix3>,
    nb_features: usize,
) -> Vec<usize>
where
    S: Data,
    S::Elem: LabelType,

Calculates the histogram of a label image.

• labels - 3D labels image, returned by the label function.
• nb_features - Number of unique labels, returned by the label function.