  In order to improve speckle noise denoising of block matching 3d filtering
(BM3D) method, an image frequency-domain multi-layer fusion enhancement method
(MLFE-BM3D) based on nonsubsampled contourlet transform (NSCT) has been
proposed. The method designs a NSCT hard threshold denoising enhancement to
preprocess the image, then uses fusion enhancement in NSCT domain to fuse the
preliminary estimation results of images before and after the NSCT hard
threshold denoising, finally, BM3D denoising is carried out with the fused
image to obtain the final denoising result. Experiments on natural images and
medical ultrasound images show that MLFE-BM3D method can achieve better visual
effects than BM3D method, the peak signal to noise ratio (PSNR) of the denoised
image is increased by 0.5dB. The MLFE-BM3D method can improve the denoising
effect of speckle noise in the texture region, and still maintain a good
denoising effect in the smooth region of the image.
