Re: [SIP-devel] images fft + contrib mkfftfilter

[DRUEL J. <joc...@li...>]

Le Jeudi 4 Septembre 2003 14:17, vous avez écrit :
> On Tue, 2 Sep 2003, DRUEL Jocelyn wrote:
> > > 	spectrum = abs(IM).*conj(IM)
> >
> > I suppose you mean: spectrum=real(IM.*conj(IM))
>
> OPS, sorry,
> not even "real" is needed.
> spectrum=IM.*conj(IM) already gives a real power spectrum
>

In theory...but Scilab still considers the spectrum matrix as imaginary:
imshow(spectrum,[]) does not work. So, I think that the "real" is compulsory.

I suggest the following contribution which is named mkfftfilter: in order to 
ease this type of spectrum filtering, the function returns commonly used 
transfert functions. The filtering is made in 3 or 4 lines:

image=gray_imread(SIPDIR+'images/ararauna.jpg');
IM=fft(image,-1);
h=mkfftfilter(image,'butterworth',20);
IM2=IM.*fftshift(h);//spectrum modification
im2=real(fft(IM2,1));
Done...

I hope it could be a good introduction to spectrum filtering.

Best regards
Jocelyn

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