John1984

I would like to ask you the following question: When we calculate the power spectrum of a N*M matrix, the result is also an N*M matrix, right? In which cases the result is an 2N*2M matrix? This question arises from the paper "TEXTURE CHARACTERIZATION USING ROBUST STATISTICS" (Russell Muzzolini etc.) page 122 (see picture). It looks like the fft is expanded and in the negative frequencies too. Thank you very much!