FFT in Matlab

Hi,

I created an image in Matlab in the following way: I created 2 vectors
that represent the image coordinates, and gave a value to each
combination of the vectors. For example: a=[-0.4:0.02:0.4], b=a,
image(y,x) is the value of a(y), b(x). Then I performed some
operations that are like Fourier transform. I got new coordinates that
were not equally spaced. So I made a grid, and interpolated the
results I had to that grid. Then I performed ifft. I got an image that
is similar to my original image, but not in the right coordinates. For
example, If in the original I had a point in the upper right corner,
in the new image it is in the middle of the image. What do I need to
do in order to get back my true image? How is it related to the
sampling frequency?

Hi Chenitz,
    It sounds like you may be using fftshift on one of your transformations 
and  not the other - I'd just check your code to see if this might be 
happening before worrying about anything more complicated.

Best of Luck - Mike

"chenitz" <chenitz@yahoo.com> wrote in message 
news:5f35af74.0501280022.b61c37f@posting.google.com...
> Hi,
>
> I created an image in Matlab in the following way: I created 2 vectors
> that represent the image coordinates, and gave a value to each
> combination of the vectors. For example: a=[-0.4:0.02:0.4], b=a,
> image(y,x) is the value of a(y), b(x). Then I performed some
> operations that are like Fourier transform. I got new coordinates that
> were not equally spaced. So I made a grid, and interpolated the
> results I had to that grid. Then I performed ifft. I got an image that
> is similar to my original image, but not in the right coordinates. For
> example, If in the original I had a point in the upper right corner,
> in the new image it is in the middle of the image. What do I need to
> do in order to get back my true image? How is it related to the
> sampling frequency?