[Numpy-discussion] fft help

Burlen Loring burlen.loring at gmail.com
Thu Dec 29 16:23:32 EST 2011

```there seems to be some undocumented restriction on dimensions as when I
work with 512x512 data things work as expected.

On 12/29/2011 09:43 AM, Torgil Svensson wrote:
> 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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