Ideal Low Pass Filter

Ideal Low Pass Filter using DFT

Description

Ideal Low Pass Filter using Discrete Fourier Transform

• Required Products: Image Processing Toolbox
• MATLAB release: MATLAB 7 (R14)

[ARJUN KUMAR]

Thanks for helping program

[Deepan chakravarrthy]

 

[martin barrera]

Thanks a lot.

[Jithin R.G]

 

[charles khoo]

Hallo, can anyone tell me how to implement this file ? It can't work.
When i run the file from editor/debug, errors appear.

[S K]

This is a perfect example of junk submission- posting some badly written homework assignments. Please remove it all from FEX, there is enough junk already.

2 charles khoo: You marked file that you couldn’t even run as excellent. I wonder what mark do you give to the function that DOES work?

[h j]

 

[Stewart Thomas]

This program is horrible. Not a single comment, no explanation of how to use. This is not even ready to be generalized.

[Duane Hanselman]

This is just a poorly done homework problem. What does ideal mean? Here is the first three lines of the file:
%Question No:5
%IDEAL LOW-PASS FILTER
function idealfilter(X,P)

[Xander Baker]

This code has no comments, but it works just spledidly -- it was designed for 2-D Images of a generic length. As a better illustration, try this code for an image with equal height and width.

% Ideal low pass filter
img = X/max(max(X));
P=[10 20 50 100];
% generate a mask to apply over the
% image's fourier transform.
% for square images, we can simplify the
% code to make a mask:
[L,W]=size(img);
for t=1:length(P)
    for i=1:L
        for j=1:L
            dFromCenter = sqrt((i-L/2)^2 + (j-L/2)^2);
            H(i,j)=double(dFromCenter<=P(t));
        end
    end
    % apply the mask over the transform
    F=fftshift(fft2(img)); % fft the image,
                    % bringing the 0
                    % frequencies to
                    % center
    G=fftshift(H.*F); % mask out outer
                    % frequencies and shift
                    % back to image state
    g=real(ifft2(double(G)));
    figure(5);
    subplot(2,2,t);
    imshow(g);
    title(sprintf('ILPF P=%1.f',P(t)));
end

[PT sad]

The worst low-pass filter ever. Not ideal at all. That's hard to believe than more than 5000 (hopeless?) people have downloaded it. Examples in the Matlab documentation are by far much better (and not poorly coded). Is FEX finally just a collection of irrelevant poor codes?

[prom etheus]

awful

[senthilkumar subramaniam]

can anyone tell me how to implement this file ? It can't work. When i run the file from editor/debug, errors appear.

[nancy m]

this is a load of crap!

[yu peter]

??

[AB C]

I think, if you wnat to use this to a full color image, you might need some changes...

%Question No:5
%IDEAL LOW-PASS FILTER

function idealfilter(X,P)
f=imread(X);
[M,N,O]=size(f);
F=fft2(double(f));
u=0:(M-1);
v=0:(N-1);
idx=find(u>M/2);
u(idx)=u(idx)-M;
idy=find(v>N/2);
v(idy)=v(idy)-N;
[V,U]=meshgrid(v,u);
D=sqrt(U.^2+V.^2);
H=double(D<=P);
G=F;
for i = 1:O
    G(:,:,i) = H.*F(:,:,i);
end
g=uint8(real(ifft2(double(G))));
imshow(f),figure,imshow(g);
end

[Alejandro Stepnik]

Hi, I am new to image processing and i need to filter some grayscale images with low and high frequency band filters.
Your code works fine but I still don't quite understand the parameter P. If I had to filter the image so that only frequencies < 6 cycles per degree where displayed on the image when viewed form 80 cm distance, then don't know how to calculate the accurate P value.
Could you give me a hint on this? I would really apreciate it

Thank you very much

[Adam Baker]

File exchange could do without this kind of submission. No explanation at all.

[Ricardo Barrios]

 

[steppenwolf Nayak]

thanks a lot.. could you clarify about the parameter P?