[2] Teramoto A, Horiba I, Sugie N. Improvement of image quality in MR image using adaptive K-nearest neighbor averaging filter[A]. Proceedings of 1997 International Conference on Information, Communications and Signal Processing[C]. 1997,1(4): 190-194.
[3] Czerwinski R N, Jones D L, O'Brien W D Jr. Ultrasound speckle reduction by directional median filtering[A]. International Conference on Image Processing[C]. 1995,1(10): 358-361.
[4] Davies E R. Image distortions produced by mean, median and mode filters[A]. IEE Colloquium on Non-Linear Signal and Image Processing[C]. 1998,6.1-5.