J = VL_IMWHITEN(I,ALPHA) approximatively whitens the power spectrum of the natural image I. The algorithm assumes that the modulus of the spectrum decays as 1/f^ALPHA (f is the frequency).

VL_IMWHITEN(I) uses ALPHA=1 (a typical value for natural images).

VL_IMWHITEN(I,ALPHA,CUTOFF) also applies a low-pass filter with cutoff frequency equal to CUTOFF x FN, where FN is the Nyquist frequency (half of the sampling frequency).