In the previous algorithm we do not use the hierarchy of structures.
We have explored many approaches for introducing a non-linear
hierarchical law in the adaptive filtering and we found that the best
way was to link the threshold to the wavelet coefficient of the
previous plane 
. We get:
and L is a threshold estimated by:
where 
is the standard deviation of 
. The function 
must return a value between 0 and 1. A possible function for t is:
if 
if a < k