Define dyadic spatial scales t j as At each spatial scale, the spectral band is defined as: where Λ(T ) represents any eigenvalue of T , and ε ∈ (0, 1) is a pre-defined threshold in Figure 2.
we can now associate with each of the spectral bands a vector subspace spanned by the corresponding eigenvectors: In the limit, we obtain the highest level of the resulting subspace hierarchy is spanned by the eigenvector associated with the largest eigenvalue of T .