MATLAB: How to normalize data from a periodogram

Question

Hello,

I need to "normalize" some data that are always going up, but I don't know how I can do that.

This is the curve (it is a chi-square periodogram):

And I need something like this:

Note: for what I need, there is no problem if I lose the data value. E.g. if the value of 0.36 becomes 0.24.

Does anyone know any method for doing this?

Answer 1

I solved the problem using linear regression:

The points below the blue line receives zero, and the value points above the blue line are subtracted by the value of the same point in the linear regression. Something like this:

if data[x] < linearRegression[x]
    data[x] = 0
else
   data[x] = data[x] - linearRegression[x]
end

Note: in this case I don't care about the value itself, I just need to see where the peak occurs.