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From: devil6601 on 31 Jul 2010 11:15
hi,

can anyone tell me how to perform 2d fft? what i understood for 2d fft is
that for each rows we perform individual fft's and place the result on the
respective rows and similarly for the columns. what i mean is suppose i
have an array of 2d data as:

0000
0110
0110
0000

now what i am trying to do is calculate fft (4 point fft instead of 16
point fft) of the first row (0000) and place the result in first row,
calculate the fft for the second row (0110) and place the result in second
row and so on. similarly for column calculate the fft for first column
(0000) and place the result in the first column and so on. so will this
work and will i get the same result as of 16 point fft?

thanks


From: Jerry Avins on 31 Jul 2010 11:21
On 7/31/2010 11:15 AM, devil6601 wrote:
> hi,
>
> can anyone tell me how to perform 2d fft? what i understood for 2d fft is
> that for each rows we perform individual fft's and place the result on the
> respective rows and similarly for the columns. what i mean is suppose i
> have an array of 2d data as:
>
> 0000
> 0110
> 0110
> 0000
>
> now what i am trying to do is calculate fft (4 point fft instead of 16
> point fft) of the first row (0000) and place the result in first row,
> calculate the fft for the second row (0110) and place the result in second
> row and so on. similarly for column calculate the fft for first column
> (0000) and place the result in the first column and so on. so will this
> work and will i get the same result as of 16 point fft?
>
> thanks
>

Have I seen this before, or did I have a prescient dream?

Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
From: Tauno Voipio on 31 Jul 2010 11:28
On 31.7.10 6:21 , Jerry Avins wrote:
> On 7/31/2010 11:15 AM, devil6601 wrote:
>> hi,
>>
>> can anyone tell me how to perform 2d fft? what i understood for 2d fft is
>> that for each rows we perform individual fft's and place the result on
>> the
>> respective rows and similarly for the columns. what i mean is suppose i
>> have an array of 2d data as:
>>
>> 0000
>> 0110
>> 0110
>> 0000
>>
>> now what i am trying to do is calculate fft (4 point fft instead of 16
>> point fft) of the first row (0000) and place the result in first row,
>> calculate the fft for the second row (0110) and place the result in
>> second
>> row and so on. similarly for column calculate the fft for first column
>> (0000) and place the result in the first column and so on. so will this
>> work and will i get the same result as of 16 point fft?
>>
>> thanks
>>
>
> Have I seen this before, or did I have a prescient dream?
>
> Jerry

You're right. The only thing that changed was the sender's name.
Both are from an Indian IP (BSNL Internet, no reverse).

Maybe he's not happy with the response and the deadline for the
homework is pressing.

--

Tauno Voipio

From: Fred Marshall on 3 Aug 2010 14:59
Tauno Voipio wrote:
> On 31.7.10 6:21 , Jerry Avins wrote:
>> On 7/31/2010 11:15 AM, devil6601 wrote:
>>> hi,
>>>
>>> can anyone tell me how to perform 2d fft? what i understood for 2d
>>> fft is

> http://www.cs.unm.edu/~brayer/vision/fourier.html

> http://fourier.eng.hmc.edu/e101/lectures/Image_Processing/node6.html

Fred
From: Dirk Bell on 3 Aug 2010 17:28
On Jul 30, 5:34 pm, glen herrmannsfeldt <g...(a)ugcs.caltech.edu> wrote:
> niyander <mightycatniyan...(a)gmail.com> wrote:
> > can anyone tell me how to perform 2d fft? what i understood for 2d fft
> > is that for each rows we perform individual fft's and place the result
> > on the respective rows and similarly for the columns. what i mean is
> > suppose i have an array of 2d data as:
> > 0000
> > 0110
> > 0110
> > 0000
>
> The FFT is separable in rectangular coordinates.  You separately
> do the X and Y transforms, in either order, to get the appropriate
> XY (2D) transform.
>
> > now what i am trying to do is calculate fft (4 point fft instead of 16
> > point fft) of the first row (0000) and place the result in first row,
> > calculate the fft for the second row (0110) and place the result in
> > second row and so on. similarly for column calculate the fft for first
> > column (0000) and place the result in the first column and so on. so
> > will this work and will i get the same result as of 16 point fft?
>
> No, it is different from a 16 point 1D FFT on the data, but it
> is the right transform for 2D data.
>
> If you think about the normal modes for a square drum head
> then you will have some idea about the results of the transform.
>
> -- glen

Actually, what he is saying will not give the same result as a 2-D
fft. After he fft's the rows, the first column is no longer (0000).

Dirk
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