Existing frequency-domain-oriented methods of parameter identification for uniform linear motion blur (ULMB) images usually dealt with special scenarios.For example,blur-kel directions were horizontal or vertical,or degraded images were of foursquare dimension.This excludes those identification methods from being applied to real images,especially to estimate undersized or oversized blur kels.Pointing against the limitations of blur-kel identifications,discrete Fourier transform (DFT)-based blur-kel estimation methods are proposed in this paper.We analyze in depth the Fourier frequency response of generalized ULMB kels,demonstratc in detail its related phase form and properties thereof,and put forward the concept of quasi-cepstrum.On this basis,methods of estimating ULMB-kel parameters using amplitude spectrum and quasi-cepstrum are presented,respectively.The quasi-cepstrum-oriented approach incresses the identifiable blur-kel length,up to a maximum of half the diagonal length of the image.Meanwhile,directing toward the image of undersized ULMB,an improved method based on quasi-cepstrum is presented,which ameliorates the identification quality of undersized ULMB kels.The quasi-cepstrum-oriented approach popularizes and applies the simulation-experiment-focused DFT theory to the estimation of real ULMB images.Compared against the amplitude-spectrum-oriented method,the quasi-cepstrum-oriented approach is more convenient and robust,with lower identification errors and of better noiseimmunity.