Circular convolution to Linear convolution.

Hi,
 I am new to this programming world, and i really need some serious help.
I have done a program in which i design a filter in frequency domain, then
i take a CT image, which is a 3d image, read each voxel and make a 1d
array. then i equal the number of samples for both the data set. so i have
equal samples. then i do convolution using fftw3 library. but what happens
is that i am doing circular convolution, I want help to do this as a
linear convolution. please help me with this. waiting for your replies.
any other data you need please let me know.

thank you.

usual process of getting the effect of linear convolution.

if x is data and h is filter

M = data length
N = filter length

then zero pad x with N-1 zeros
zero pad h with M-1 zeros

perform FFT of both x and h with length >= M+N-1

do multiplication in complex domain to get the effect of filter.

perform IFFT and get back y(n)

hope this helps,

regards
bharat pathak

Arithos Designs
www.Arithos.com

%--- DSP design consultancy and training company ------------








>Hi,
> I am new to this programming world, and i really need some serious
help.
>I have done a program in which i design a filter in frequency domain,
then
>i take a CT image, which is a 3d image, read each voxel and make a 1d
>array. then i equal the number of samples for both the data set. so i
have
>equal samples. then i do convolution using fftw3 library. but what
happens
>is that i am doing circular convolution, I want help to do this as a
>linear convolution. please help me with this. waiting for your replies.
>any other data you need please let me know.
>
>thank you.
>
>
>