pro freq_ana
;Example in p.122-123. Frequency analysis
S=100 ;Spatial Frequency
N=250 & M=350 ;Array dimensions
;h=Replicate(1.0/81,9,9) ;3x3 averaging array
;h=[[-1,0,1],[-2,0,2],[-1,0,1]]; Sobel
;h=[[-1,0,1],[-1,0,1],[-1,0,1]]; Prewitt
;h=[[0,1,0],[1,-4,1],[0,1,0]]; Laplacian
h=[[-1,-1,-1],[-1,8,-1],[-1,-1,-1]]; Isotropic Laplacian
hp=ZeroPad(h,N,M) ;Pad to size NxM
HF=FFT(hp)
HM=ABS(HF*M*N) ; Find normalized magnitude
fx=Findgen(N)/N*S ;Horizontal frequency scale
fy=Findgen(M)/M*S ; Vertical frequency scale
Window,/Free, Xsize=350, Ysize=250
Shade_surf,HM
Window,1,/Free,Xsize=350,Ysize=250
Shade_surf,shift(HM,125,175)
End