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From: Simon on 28 Apr 2010 23:30
Hi All,

I've done some basic image filtering in the frequency domain (High Pass and Low Pass) as part of a course project, following the methods outlined in the book Digital Image Processing Using Matlab (DIPUM).

I would like to be able to desribe the filters in terms of their cutoff frequency in cycles per picture height, or c/ph, which is how we've discussed image frequencies in this course.

However, I'm not clear on the relationship of DIPUM's parameters to frequencies in these units. For example, suppose I make a gaussian filter with the following code, where PQ(1) and PQ(2) are the zero-padded image's height and width respectively:

D0 = 0.01*PQ(2);
H2 = lpfilter('gaussian', PQ(1), PQ(2), D0);

The function lpfilter ultimately creates a filter with the following line:

H = exp(-(D.^2)./(2*(D0^2)));

where D is the meshgrid of distances from the filter's origin. So, can anyone figure out what the filter's cutoff frequency would be in c/ph?

Thanks.
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