Low pass filter for image
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I want to create a lowpass filter (circle!) for an 110 x 160 pixel image.
The cut-off frequency should be 0.13/pixel.
What I tried so far:
bricks = im2double(imread("bricks.jpg"));
y1 = fft2(bricks);
[N, M] = size(bricks);
u = -1/2:1/M:1/2-1/M;
v = -1/2:1/N:1/2-1/N;
[U, V] = meshgrid(u, v);
d = U.*U/(0.13*0.13) + V.*V/(0.13*0.13);
mask = d <= 1;
yt1 = fftshift(y1);
yt1 = yt1.*mask;
low_filtered_image = ifft2(ifftshift(yt1), 'symmetric');
The spectrum of my filter and the filtered spectrum look like this:
That gives me the following result for my lowpass filtered image:
But I am not sure if this is correct.
回答（1 个）
Image Analyst
2023-6-24
1 个投票
Use fft2, then zero out anything beyond 0.13. I'll leave it to you to figure out what index that is in the spectral image.
This looks like a homework problem. If you have any questions ask your instructor or read the link below to get started:
Obviously we can't give you the full solution because you're not allowed to turn in our code as your own.
4 个评论
Dominik Deml
2023-6-24
Image Analyst
2023-6-24
The return value of fft2 is the frequency image. Read up on it.
Dominik Deml
2023-6-25
编辑：Dominik Deml
2023-6-25
Image Analyst
2023-6-25
Then use a higher value so that less of the spectral image is erased. See attached demos.
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2023-6-24
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