For solving the problem of displacement estimation for out-of-focus blurred images

the method of image registration based on phase-only correlation is introduced. The method is based on the translation characteristics of Fourier transform to search translation between images

the inverse Fourier transform of the normalized cross power spectrum of pairs images is a two dimension impulse function

and the translation displacement between images can be finely retrieved from the location of the correlation peak. The method of image registration of phase-only correlation combined with degradation model of spatially variant blur

the mathematical expression of PSF and OTF for out-of-focus blur is described

and the effect of blur on registration is discussed. The relation between variance of normalized cross power spectrum and degradation of blurred images is demonstrated

which is only dependent on the displacement between images and not on the blur in image.The experimental result shows that this method can detect sub-pixel-level shift parameters accurately and efficiently

the maximum error of registration is only 0.339-pixel. It is efficient and satisfies the system requirements.