Focused on the frequency aliasing and shift-variance of contourlet transform,a shift-invariant (non-subsampled) non-aliasing contourlet transform(NS-NACT) is proposed based on non-subsampled non-aliasing pyramidal filter banks(NS-NPFB) and undecimated directional filter banks(UDFB).Based on the NS-NACT,an adaptive-threshold denoising algorithm is designed.Experimental results show that this algorithm can raise the PSNR about 0.65 dB and 3.47 dB (when noise variance is 30),respectively,and effectively elimin...