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From: Mukeshwar on 21 Apr 2010 23:00
When adding gaussian noise to image i receive this error message and it only happens with some images. Heres the codes



s= 128; % Size of each matrix to display
n = 4; % number of rows and cols in the figure
for M = 0:n-1 % no. of cycles on y-axis
for N = 0:n-1 % no. of cycles on x-axis
F = zeros(s); % F is the Fourier transform array ...

% ... which is all zeros apart from a single element ...
F(M + 1, N + 1 ) = 1; % at this point
% ... and the symmetrical elements for the negative frequencies
F(mod(-M, s) + 1, N + 1 ) = 1;
F(M + 1, mod(-N, s) + 1) = 1;
F(mod(-M, s) + 1, mod(-N, s) + 1) = 1;

% Now it's set up, do the inverse FT
imcomp = ifft2(F); % f is the Fourier component in the spatial domain

subplot(n, n, n*M + N + 1);
imshow(imcomp, []);
end

end
im=imread('5w','jpg');
im = im(1:2:397, 1:2:568);
figure; imshow(im);
F=fft2(im);
figure;
imshow(log(abs(F)), []);
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);

figure;
cycles = [0 1 2 4 8];
n = length(cycles);
for p = 1:n
for q = 1:n
keep = abs(cx) <= cycles(p) & abs(cy) <= cycles(q);
partF = F .* keep;
partim = ifft2(partF);
subplot(n, n, n*(p-1) + q);
imshow(partim);
end
end
sigma = 0.09; % Width of the Gaussian, in radians/pixel
ms = exp(-(fx.^2 + fy.^2)/(2*sigma^2));
figure; imshow(log(ms), []);
smoothF = F .* ms; % multiply FT by mask
smooth = ifft2(smoothF); % do inverse FT
imshow(smooth, []);

it works fine for some images but smaller images it crashes and gives
? Error using ==> times Matrix dimensions must agree"
Please help
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