How do you set every other row as well as every other column to zero?

Using a phantom...

P = phantom('Modified Shepp-Logan',256);

And plotting it with a fourier transform

n = 256;

Fp = fft2(P,n,n);

How would I remove certain rows and columns?

Answer 1

[Dave B]

To remove every other column, set it to empty. You can do "every other" generally using A:2:B where A is the first value and B is the last value, and you can stick this in as an index.

a=reshape(1:25,5,5)

a = 5×5

1 6 11 16 21 2 7 12 17 22 3 8 13 18 23 4 9 14 19 24 5 10 15 20 25

a1=a;
a1(1:2:end,:)=[] % remove every other row

a1 = 2×5

2 7 12 17 22 4 9 14 19 24

a2=a;
a2(2:2:end,:)=[] % remove every other row starting at the second row

a2 = 3×5

1 6 11 16 21 3 8 13 18 23 5 10 15 20 25

a3=a;
a3(:,1:2:end)=[] % remove every other column

a3 = 5×2

6 16 7 17 8 18 9 19 10 20

a4=a;
a4(:,1:2:end)=0 % set every other row/column to 0

a4 = 5×5

0 6 0 16 0 0 7 0 17 0 0 8 0 18 0 0 9 0 19 0 0 10 0 20 0

% If you really feel like you have to do both at once, you can. But it
% would be much easier to just do rows and columns sequentially.
a5=a;
[r,c]=meshgrid(1:size(a5,1),1:size(a5,2));
ind=sub2ind(size(a5),r(mod(r,2)==0 | mod(c,2)==0),c(mod(r,2)==0 | mod(c,2)==0));
a5(ind)=0

a5 = 5×5

1 0 11 0 21 0 0 0 0 0 3 0 13 0 23 0 0 0 0 0 5 0 15 0 25

Note if your goal is to resize the image or the fft by half, imresize will give you more options