Vaizdas:Antialiased-sinc.png

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Antialiased-sinc.png (13 KB, MIME tipas: image/png)

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La bildo estas kopiita de wikipedia:en. La originala priskribo estas:

sinc filter antialiased chessboard


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If the current image is the same as when I (Loisel 23:40 14 Jul 2003 (UTC)) wrote this comment, the following Matlab code was used to generate the image:

function Z=filteredchessboard(n,a);
foo=(1:n)*128.0/n;
m=size(foo,2);
disp('Initializing X, Y')
for i=1:m
    X(:,i)=(foo-64.0)';
    Y(i,:)=foo;
end
disp('Generating unfiltered chessboard')
T=1.0./(Y/2048.0+0.001);
Z=T.*(X/128.0);
I0=floor(T);
J0=floor(Z);
K=I0+J0;
C=mod(K,2);
disp('Calculating Fhat')
Fhat=fft2(C);
f1=floor(m/a);
f2=n-f1;
f1=f1+1;
f2=f2+1;
disp('Zeroing middle frequencies')
Fhat(f1:f2,:)=0;
Fhat(:,f1:f2)=0;
disp('Inverse Fourier transform & output')
Z=real(ifft2(Fhat));

The returned matrix (e.g. from filteredchessboard(1024,20)) can be viewed with, eg,

image(10*Z')

I then clamped the image like so:

X=max(min(1,Z),0);

in Matlab. Then I took a submatrix of size 128 (e.g., X(1:10:(10*128),1:10:(10*128))) and I wrote it to a file using dlmwrite. Then I wrote a short C program to extract the floating point numbers and convert them into a .pgm file. Lastly, using Gimp, I converted the image to rotate the image 90 degrees and save it to png.

date/time username edit summary
19:21, 22 December 2004 en:User:Quadell (tagged)
00:21, 15 July 2003 en:User:Loisel (updated comments for updated image)
23:40, 14 July 2003 en:User:Loisel (signed)
23:39, 14 July 2003 en:User:Loisel (<tt> -> <pre>)
23:22, 14 July 2003 en:User:Loisel (howto reproduce image)
23:18, 14 July 2003 en:User:Loisel (<a href="/wiki/Sinc_filter" title="Sinc filter">sinc filter</a> antialiased chessboard)

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