From: Ian Scott <ian.scott@st...> - 2005-12-02 10:35:20
Timothy Chan wrote:
> Thanks for all your help and putting up with my stupid questions. I have
> successfully used both fft fwd and bwd now on a number of images so that has
> been a great help.
> There is one file in particular that I cannot seem to run the fft on, and
> when I do I get the message "assertion failure '!'you probably gave a signal
> size not of the form 2^p 3^q 5^r" Can you explain to me what this means and
> how I can get around it? If there was somebody here that I could ask I
> certain would, but unfortunately there isn't.
We don't mind questions about VXL - its just non-VXL programming and
tool-chain management questions we would rather avoid.
However, your questions would be better sent to vxl-users.
I'm not an expert on the FFT code, but at a guess the size of your image
needs to be (2^pi*3^qi*5^ri,2^pj*3^qj*5^rj), where all the variables are
Most FFT algorithms require your image to be sized as a power of 2, in
order to have a Fast Fourier Transform rather than just a Fourier
Transform. VXL's FFT appears to be rather generous in allowing factors
of 3 and 5 as well. I suspect the solution is to pad your image with
some values so that it is the next appropriate size. Some of the links
at http://www.google.com/search?q=padding+data+for+FFT appear to suggest
that padding with 0 is generally acceptable.
If your image is
> -Tim Chan