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what is wrong here? ??? Error using ==> times Matrix dimensions must agree.

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i = imread('peppers.png');
red = i(:,:,1);
green = i(:,:,2);
blue = i(:,:,3);
subplot(4,2,1);imshow(i);title('original image');
subplot(4,2,2);imshow(red);title('red');
subplot(4,2,3);imshow(green);title('green');
subplot(4,2,4);imshow(blue);title('blue');
A = cat(3,red,green,blue);
subplot(4,2,5);imshow(A);title('Combined again');
Fi=fftshift(double(A));
[m,n]=size(A);
[x,y]=meshgrid(1:n,1:m);
x=x-(n+1)/2;
y=y-(m+1)/2;
d=sqrt(x.^2+y.^2);
d0=30;
ghpf=1-exp(-d.^2/(2*d0.^2));
j=ifft2(fftshift(Fi.*ghpf));
subplot(4,2,6);imshow(j);title('new');
the output here is :
??? Matrix dimensions must agree.
Error in ==> testRgb at 27
j=ifft2(fftshift(Fi.*ghpf));

Accepted Answer

Image Analyst
Image Analyst on 9 Aug 2020
Never do this with an image:
[m,n]=size(A);
Why not? Because if A is RGB, which yours is, then your n is the number of columns times the number of color channels. So it's basically 3 times the number of columns, not the number of columns like you thought.
Do this instead:
[rows, columns, numberOfColorChannels] = size(A);
I'm also begging you to not have your code look like an alphabet soup mess of a program. Use descriptive variable names (not single letters), and add lots of comments. I would not hire a person who wrote code that doesn't follow those two requirements of good programming.

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More Answers (1)

Sulaymon Eshkabilov
Sulaymon Eshkabilov on 9 Aug 2020
Hi,
There is two small but crucial errs - see the command below:
%...
Fi=fftshift(double(A)); % NOTE your assigned variable name
[m, n, ooo]=size(A); % 1st ERR => NB: size of A is 225-by-225-by-3. Thus, you'd need the 3rd output as well
[x,y]=meshgrid(1:m,1:n);
x=x-(n+1)/2;
y=y-(m+1)/2;
d=sqrt(x.^2+y.^2);
d0=30;
ghpf=1-exp(-d.^2/(2*d0.^2));
% j=ifft2(fftshift(fi.*ghpf)); % 2nd ERR: Need to be Fi instead of fi
j=ifft2(fftshift(Fi.*ghpf));
subplot(4,2,6);imshow(j);title('new');
Good luck

  3 Comments

Radwan Alerqsousi
Radwan Alerqsousi on 9 Aug 2020
Thank you sulaymon ,
i did what you told me and i still have the exact same Err.
i = imread('peppers.png');
red = i(:,:,1);
green = i(:,:,2);
blue = i(:,:,3);
subplot(4,2,1);imshow(i);title('original image');
subplot(4,2,2);imshow(red);title('red');
subplot(4,2,3);imshow(green);title('green');
subplot(4,2,4);imshow(blue);title('blue');
A = cat(3,red,green,blue);
subplot(4,2,5);imshow(A);title('Combined again');
Fi=fftshift(double(A));
[m,n, ooo]=size(A);
[x,y,]=meshgrid(1:n,1:m);
x=x-(n+1)/2;
y=y-(m+1)/2;
d=sqrt(x.^2+y.^2);
d0=30;
ghpf=1-exp(-d.^2/(2*d0.^2));
%j=ifft2(fftshift(Fi.*ghpf));
j=ifft2(fftshift(Fi.*ghpf));
subplot(4,2,6);imshow(j, []);title('new');
thanks anyway
Sulaymon Eshkabilov
Sulaymon Eshkabilov on 9 Aug 2020
You have another typo:
[x,y,]=meshgrid(1:n,1:m); must be
[x,y]=meshgrid(1:n,1:m);

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