How can I determine noise (threshold ) in my Im having one matrix ( it which is auto correlation product of two FFT transforms of one fits image ( astronomical image )? When i succeed to find value of noise, i . In that matrix you could easily find three 3 peaks. One largest in center, and two around central peak. Main problem is determining those peaks. I tried to could find noise like sum of all date divided central ( largest ) peak by number of datasearching for max value in matrix. But, but main when i want to find out size of central peak is very large i`m having problem due to noise. Im not sure where noise begin and it corrupts resultwhere peak end. Is there any other waySo, my question is how to find noise value? And when i find it, peaks will be above that value.