Image:Antialiased-sinc.png
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Antialiased-sinc.png (128 × 128 pixel, file size: 13 KB, MIME type: image/png)
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.
File history
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- (del) (cur) 13:34, 30 September 2005 . . Riumplus (Talk | contribs) . . 128×128 (12,995 bytes) (Losslessly recompressed the image, shrinking file size by 2%)
- (del) (rev) 01:01, 15 July 2003 . . Loisel (Talk | contribs) . . 128×128 (13,271 bytes) (bugfix)
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