Just to add some additional information to my previous question which can clarify further:
I would like to filter out 1/2 or 1/3 of the amplitudes of the frequency components whithin the orthogonal area of the following image:
https://www.dropbox.com/s/r6p57oj0cacjpoq/La%20place%20domain%20of%20signal%20intensity%20curves.jpg