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Kristen
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imfilter speed for volume

Asked by Kristen
on 9 Oct 2013
I'm working on an algorithm, which requires filtering of a 3D matrix (non-sparse, 512^3) to find edges.
I only want to find edges in each slice, so I have been doing the following:
% 2D loop appaoch
[x,y]=ndgrid(floor(-3*sigma):ceil(3*sigma),floor(-3*sigma):ceil(3*sigma));
DGauss=-(x./(2*pi*sigma^4)).*exp(-(x.^2+y.^2)/(2*sigma^2));
filteredVolume = zeros(size(vol))
for n = 1:size(vol,3)
filteredVolume(:,:,n) = imfilter(vol(:,:,n),DGauss,'conv','symmetric');
end
I also tried to do the same by calling imfilter on the entire volume:
% 3D matrix approach
filteredVolume = imfilter(vol,DGauss,'conv','symmetric');
I compared the performance of both of these approaches, but the loop version is significantly faster (6.5 seconds to 20 seconds).
Should this behavior be expected? If so, why?

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