Merge branch 'main' into studipsync

6 files were unmodified
5 files were created

lecture/3. Signal Processing/code_signal_processing.jl

@@ -0,0 +1,46 @@
+using Images
+using PyPlot
+using FFTW
+
+N = 64
+x = shepp_logan(N)
+
+figure(1)
+clf()
+subplot(2,2,1)
+imshow(x)
+
+X = fft(x)
+subplot(2,2,2)
+imshow(abs.(X))
+
+Y = fftshift(X)
+subplot(2,2,3)
+imshow(abs.(Y))
+
+Y[1:div(N,4)+1,:] .= 0.0
+Y[3*div(N,4):end,:] .= 0.0
+Y[:,1:div(N,4)+1] .= 0.0
+Y[:,3*div(N,4):end] .= 0.0
+
+subplot(2,2,4)
+imshow(abs.(Y))
+
+
+figure(2)
+clf()
+imshow(abs.(ifft(ifftshift(Y))))
+
+
+
+function mydft(x)
+  N = length(x)
+  y = zeros(ComplexF64,N)
+
+  for l=1:N
+    for n=1:N
+      y[l] += x[n]*exp(-2*pi*im*(n-1)*(l-1)/N)
+    end   
+  end
+  return y
+end