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Re: backprojection [message #52165]

Fri, 19 January 2007 01:52

Wox
Messages: 184
Registered: August 2006

Senior Member

On 18 Jan 2007 08:49:10 -0800, "Mike" <Michael.Miller5@gmail.com>
wrote:

> Don't forget that the inverse radon transform is not the inverse
> of forward projection. The filtered backprojection is the
> inverse. Filtered backprojection generally proceeds by four
> steps: 1) calculate the Fourier transform of the projection data,
> 2) apply the appropriate filter, 3) calculate the inverse Fourier
> transform to get filtered projections, 4) backproject the
> filtered projections to get an image.

<snip>

> ;; apply the filter to each row of the sinogram
> FOR a = 0,Nangles-1 DO BEGIN
> row = sgplane[*,a]
> ftrow = FFT(row)
> ftfilteredrow = ft_filter * ftrow
> filteredrow = FFT(ftfilteredrow, /INVERSE)
> sgplane[*,a] = filteredrow
> ENDFOR

<snip>

To clarify: the filter shown is similar to the RamLak filtering in
real space (using convolution instead of multiplication) on Mark
River's web-site:
http://www-fp.mcs.anl.gov/xray-cmt/tomo_filter.htm

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[Message index]

		Re: backprojection By: Wox on Fri, 19 January 2007 01:52
		Re: backprojection By: Marc Reinig on Thu, 18 January 2007 17:53
		Re: backprojection By: Mike[2] on Thu, 18 January 2007 08:49
		Re: backprojection By: TimLS on Thu, 18 January 2007 00:40
		Re: backprojection By: Wox on Wed, 17 January 2007 08:32
		Re: backprojection By: David Fanning on Wed, 17 January 2007 07:11

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