y-axis are still inverted despite using fftshift

3 次查看（过去 30 天）
Nishant Pathak
Nishant Pathak 2021-11-20
评论： Dave B 2021-11-20
I have used the Matlab codes for simulating a phase screen. However, as you can see in the figure, y-axis are still inverted despite using fftshift. Please resolve this issue.
M = 3001;
a=3;
d = (M-1)/2; fx = (-d:d);
kx = (ones(2*d+1,1)*fx).^2; K = sqrt(kx+transpose(kx));
D = K.^(-a);
D(d+1,d+1) = 0;
R = randn(2*d+1)+1i*randn(2*d+1);
PS = (fft2(fftshift(sqrt(D).*R)));
figure(1); imagesc(abs(PS)); colormap(gray);title('Phase screen');

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回答（1 个）

Dave B
Dave B 2021-11-20
编辑：Dave B 2021-11-20
Your code doesn't run and you didn't include an image, but in general, when you call imagesc it will plot in ij coordinates, meaning that 0,0 is at the top left corner of the axes. To switch to traditional xy coordinates, simple use:
axis xy
(after calling image)
Alternatively, you can control the YDir property on the axes:
set(gca,'YDir','normal')
  2 个评论
Dave B
Dave B 2021-11-20
Ran in:
I just added my answer to the bottom of your code, is this not what you're looking for?
M = 3001;
a=3;
d = (M-1)/2;
fx = (-d:d);
kx = (ones(2*d+1,1)*fx).^2;
K = sqrt(kx+transpose(kx));
D = K.^(-a);
D(d+1,d+1) = 0;
R = randn(2*d+1)+1i*randn(2*d+1);
PS = (fft2(fftshift(sqrt(D).*R)));
figure(1); imagesc(abs(PS));
colormap(gray);
title('Phase screen');
axis xy

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