On Feb 7, 4:51 pm, "PeterOut" <MajorSetb...@excite.com> wrote:
> When I get the Fourier transform of a 1D vector, with FFTW, the peakin the Fourierspectrum (or DC component) is at one end with the
> adjacent frequency component at the other end. E.g. here is a typical
> Fourier spectrum.
>
> 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 0, 0, 10, 20, 30, 40, 50, 60,
> 70 ,80, 90
>
> It is not clear to me why it is not
>
> 0, 10, 20, 30, 40, 50, 60, 70 ,80, 90, 100, 90, 80, 70, 60, 50, 40,
> 30, 20, 10, 0.
>
> With images, the low frequency components are in the corners instead
> of the middle.
>
> Is this how I should have the FT is input if I want to get an inverse
> FT? If so, exactly where should the DC component go in the input
> matrix for a 2D FT, top-left, top-right, bottom-left, bottom-right?
> What low frequency components should go in the other corners?
> Presumably, if you zero pad, the zeros go in the middle. I tried
> taking a 2D FT with the DC component in the middle and rotating the
> quadrants by 180 degrees. The output look like I would have expected
> except that every other element in the horizontal direction was zero.
>
> Many thanks in advance,
> Peter.
Many thanks to Hendrik and Mark for their very helpful replies. They
solved the problem I was addressing.