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Convolution [message #26609]

Tue, 11 September 2001 05:22

Kay Bente
Messages: 9
Registered: September 2001

Junior Member

Hi

I have to convolute a 256x256x128 Floating Point array with a 3D Gaussian
Kernel of ~ 30x30x30, this lasts round about 45Minutes. So my question is,
if there is any way how i can speed this up. I tried to separate this in
each dimension with a 1D Kernel, but I don�t know if I have done this
correct (cause the procedure hangs up after a few loops)

I know that the Convolution of two functions is a Multiplication in Fourier
Space, but how can I do this with discrete arrays, do I have to enlarge my
kernel to the size of the array i want to smooth? If so, the creation of the
kernel with the dimensions of my array nearly lasts as long as the normal
convolution :-(

So i would be very happy about any hints!!

This is how I tried it
FUNCTION Gauss3D, mat, n, s
;n = Size Of Array
;s = Sigma

;Gauss Kernel is completely circularly symmetric operator
;=> Convol in each dimension with a 1D Kernel

;Create Kernel
a = DindGen(n)-(n/2)
print,a
kernel = Exp(-(Temporary(a))^2/(2.*s^2))/(Sqrt(2.*!PI)*s)

tstart=SysTime(1)
s=Size(mat,/Dimensions)

mat2=FltArr(s(0),s(1),s(2))

;Convol in X,Y
FOR i=0, s(2) DO BEGIN
buffer=mat(*,*,i)
buffer1=Convol(buffer,kernel,Total(kernel))
buffer1=Convol(buffer1,Rotate(kernel,1),Total(kernel))
mat2(*,*,i)=Temporary(buffer1)
ENDFOR

;Convol in Z
FOR i=0, s(1) DO BEGIN
buffer=mat2(*,i,*)
buffer1=Convol(buffer,kernel,Total(kernel))
mat2(*,i,*)=Temporary(buffer)
ENDFOR
Return, mat2
END

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[Message index]

		Convolution By: Kay Bente on Tue, 11 September 2001 05:22
		Re: convolution By: Chris[1] on Fri, 28 March 2003 08:17
		Re: convolution By: Vince Hradil on Fri, 25 April 2008 06:29
		Re: convolution By: sarah[1] on Mon, 12 May 2008 18:56
		Re: convolution By: d.poreh on Fri, 25 April 2008 01:15
		Re: convolution By: Chris[5] on Tue, 20 May 2008 04:31
		Re: convolution By: Chris[5] on Tue, 20 May 2008 03:49
		Re: convolution By: sarah[1] on Mon, 19 May 2008 15:32
		Re: convolution By: David Fanning on Mon, 12 May 2008 19:31

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