MAINT: reuse code from _sigma_est_dwt within _wavelet_threshold
MAINT: reuse code from _sigma_est_dwt within _wavelet_threshold

vighneshbirodkar/scikit-image,vighneshbirodkar/scikit-image,vighneshbirodkar/scikit-image,paalge/scikit-image,paalge/scikit-image,paalge/scikit-image