# [Numpy-discussion] fft help

Torgil Svensson torgil.svensson at gmail.com
Thu Dec 29 12:43:25 EST 2011

```Sorry, i should have looked at your image. A few test you can do is

1) does ifft2 give you back the original image?  (allclose returned
True for a little test I did here)
2) does scipy.fftpack.fft2 yield the same result?

//Torgil

On Thu, Dec 29, 2011 at 6:32 PM, Burlen Loring <burlen.loring at gmail.com> wrote:
> hmmph, I used both fftn and fft2, they both produce the same result. Is
> there a restriction on the dimension of the input? power of 2 or some such?
>
> On 12/29/2011 07:21 AM, Torgil Svensson wrote:
>> This is because fft computes one-dimensional transforms (on each row).
>>
>> //Torgil
>>
>>
>> fft(a, n=None, axis=-1)
>>      Compute the one-dimensional discrete Fourier Transform.
>>
>> fft2(a, s=None, axes=(-2, -1))
>>      Compute the 2-dimensional discrete Fourier Transform
>>
>> fftn(a, s=None, axes=None)
>>      Compute the N-dimensional discrete Fourier Transform.
>>
>>
>> On Wed, Dec 28, 2011 at 10:05 PM, Burlen Loring<burlen.loring at gmail.com>  wrote:
>>> Hi
>>>
>>> I have an image I need to do an fft on, I tried numpy.fft but results are
>>> not what I expected, and differ from matlab.
>>>
>>> My input image is a weird size, 5118x1279, I think numpy fft is not liking it. In
>>> numpy the fft appears to be computed multiple times and tiled across the
>>> output image. In other words the pattern I see in matlab fft is tiled
>>> repeatedly over numpy fft output. Any idea on what I'm doing wrong?
>>>
>>> you can see repeated pattern in the top panel of this image which also has
>>> the input in the bottom panel.
>>> http://old.nabble.com/file/p33047057/fft_uex.png  fft_uex.png
>>>
>>> tx
>>>
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```