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How do I change from Square to CIrcle?

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This fresnel diffraction simulation for a square aperture. I need to change it to work with a circle aperture. I need to help to change this step:
u0(257-w*20:256+w*20,257-w*20:256+w*20)=1; % setup aperture
This for a square and how i convert it to a circle?
Thank you.
The code is:
2d propagation from square apertures
ii=sqrt(-1) lambda= .365; % wavelenght [µm] z=1; % distance [µm] w=1; % width of slit is 2*w [µm]
x=-12.75:0.05:12.8; % setup spatial axis [µm] freqx=-10:20/512:10-1/512; % setup frequency axis [1/µm] freqy=freqx;
u0=zeros(512); % field at z=0 a0=zeros(512); % angular spectrum at z=0 H=zeros(512); % transfer function az=zeros(512); % angular spectrum at z=z uz=zeros(512); % field at z=z
for nx=1:512 % setup transfer function for ny=1:512 H(nx,ny)=exp(ii*2*pi*(z/lambda)*... sqrt(1-(lambda*freqx(nx))^2-(lambda*freqy(ny))^2)); end end
u0(257-w*20:256+w*20,257-w*20:256+w*20)=1; % setup aperture a0=(fftshift(fft2(u0))); % fourier transform az=a0.*H; % multiply with transfer function uz=ifft2(fftshift(az)); % inverse fourier transform p=uz.*conj(uz);
figure(1) plot(x, p(:,256)); % plot of cross-section of intensity at z xlabel('x'); ylabel('I');
figure(2) imagesc(x, x, p); %diffraction pattern at z xlabel('x'); ylabel('y'); colormap(gray); colorbar;

Accepted Answer

Image Analyst
Image Analyst on 3 May 2014
See code examples for creating a circle in the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F. You can adapt them as needed.
  8 Comments
Image Analyst
Image Analyst on 14 Mar 2020
Where is your new question (so we don't keep sending Maitham emails)? Your link above no longer works.
yellowMask = rgbImage(:,:,1) == 255 & rgbImage(:,:,2) == 255 & rgbImage(:,:,3) == 0;
yellowMask = imfill(yellowMask, 'holes');
yellowMask = bwareafilt(yellowMask, 1);
props = regionprops(yellowMask, 'Centroid', 'EquivDiameter');
viscircles(props.Centroid, props.EquivDiameter/2);
Dina Abd El-twab
Dina Abd El-twab on 14 Mar 2020
this code didn't give me what i want ,could you please open this link , Iam gonna attach what happened in this link now to contact there

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