[Insight-developers] Consistency in the output of forward/inverse FFT image filters

[Cory Quammen]

Ok, it turns out that if the real input image has an even dimension,
the n/2 element is purely real. That doesn't mean the converse is
true, but the odds of an odd-sized image producing an imaginary value
at element floor(n/2) is probably very small.

Cory

On Fri, Aug 19, 2011 at 12:00 PM, Cory Quammen <cquammen at cs.unc.edu> wrote:
> Gaetan,
>
> Do you have any ideas for neat tricks to figure out what the full
> dimension of the transformed image should be given the half image? The
> problem is that an image with size n (n even) yields a half image that
> is the same size as the half image produced for an image with size
> n+1.
>
> Currently, the FFT filters have a flag ActualXDimensionIsOdd that is
> used to resolve this ambiguity. It would be fantastic if users didn't
> have to set this to get the correct behavior. I haven't yet thought of
> a way to figure out the full image size automatically, and Googling
> hasn't revealed anything.
>
> Thanks,
> Cory
>
> On Fri, Aug 19, 2011 at 11:10 AM, Cory Quammen <cquammen at cs.unc.edu> wrote:
>> [snip]
>>>>
>>>> That's a good suggestion that would simplify things. Are you proposing
>>>> to make the VNL FFT filter always produce a half output image for real
>>>> inputs?
>>>
>>> That's what I'm proposing.
>>> It may have a cost for vnl filters, but hopefully it will be compensated by
>>> the lower amount of memory required for further transformations in the
>>> frequency domain.
>>
>> Okay, sounds good to me. I'll get to work on implementing this.
>>
>> Cory
>>
>> --
>> Cory Quammen
>> Research Associate
>> Department of Computer Science
>> The University of North Carolina at Chapel Hill
>>
>
>
>
> --
> Cory Quammen
> Research Associate
> Department of Computer Science
> The University of North Carolina at Chapel Hill
>



-- 
Cory Quammen
Research Associate
Department of Computer Science
The University of North Carolina at Chapel Hill