cycles/pixel to cycels/degree

Hi everyone,

I'm a new Matlab user looking for code to change my images from cycles/pixels to cycles/degree. Any suggestions?

Thanks! Rachel

Answer 1

[Dr. Seis]

See this link:

http://www.cogs.susx.ac.uk/courses/acv/matlab_demos/fft_image_demo.html

About half way down:

F = fft2(image);

nx = size(F, 2);
ny = size(F, 1);
cxrange = [0:nx/2, -nx/2+1:-1];        % cycles across the image
cyrange = [0:ny/2, -ny/2+1:-1];
[cx, cy] = meshgrid(cxrange, cyrange);

fxrange = cxrange * 2*pi/nx;           % radians per pixel
fyrange = cyrange * 2*pi/ny;
[fx, fy] = meshgrid(fxrange, fyrange);

Is this what you want instead?

[Rachel]

Thanks for responding Elige. Part of the problem is that I'm such a newbie I'm not sure what code I need. I'm a vision researcher (with no programming background) interested in analyzing the spatial frequency content of a .pbm image depicting a man-made scene (i.e., a cityscape). I'm using the following Matlab FFT code:

I = imread('image.pbm');

F = fft2(double(I));

A = fftshift(F);

L = log2(S);

A = abs(L);

imagesc(A)

Since my last posting I've figured out that when I histogram my 2D power specturm of A I'm actually getting the average spatial frequency of the image in cycles/degree. From here all I want to do is add on code that will then take this information and convert it to cycles/degree. So for example, if my city image is on average 10 cycles/pixels, how do I figure out what this is in cycles/degree?