POWER SPECTRUM of IMAGES in IDL

PRO POWER_SPECTRUM_EX
im = [64,64]
file = FILEPATH('abnorm.dat',SUBDIRECTORY =['examples','data'])
f = READ_BINARY(file,DATA_DIM=im)
sz = 2*im
DEVICE, DECOMPOSED = 0
loadct, 0
f1 = FFT(f)
center = im/2 + 1
fs = SHIFT(F1,center)
ps = ABS(fs)^2
sps = ALOG10(ps)
WINDOW,0,XSIZE = SZ[0],YSIZE = SZ[1],TITLE = 'POWER SPECTRUM'
TVSCL,CONGRID(sps,sz[0],sz[1])
END