Image:Antialiased-sinc.png
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sinc filter antialiased chessboard
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) |
[edit] Historio de la dosiero
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- (del) (cur) 13:34, 30 September 2005 . . en:User:Riumplus Riumplus ( en:User_talk:Riumplus Talk) . . 128x128 (12995 bytes) (Losslessly recompressed the image, shrinking file size by 2%)
- (del) (rev) 01:01, 15 July 2003 . . en:User:Loisel Loisel ( en:User_talk:Loisel Talk) . . 128x128 (13271 bytes) (bugfix)
File history
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| Date/Time | Dimensions | User | Comment | |
|---|---|---|---|---|
| current | 16:53, 18 March 2006 | 128×128 (13 KB) | Maksim | (La bildo estas kopiita de wikipedia:en. La originala priskribo estas: sinc filter antialiased chessboard {{GFDL}} If the current image is the same as when I (Loisel 23:40 14 Jul 2003 (UTC)) wrote this comment, the following Matlab co) |
