TAILIEUCHUNG - Biosignal and Biomedical Image Processing MATLAB-Based Applications phần 7

Tham khảo tài liệu 'biosignal and biomedical image processing matlab-based applications phần 7', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Wavelet Analysis 201 Figure Application of the dyadic wavelet transform to nonlinear filtering. After subband decomposition using an analysis filter bank a threshold process is applied to the two highest resolution highpass subbands before reconstruction using a synthesis filter bank. Periodic convolution was used so that there is no phase shift between the input and output signals. an analyze1 x h0 4 Set the threshold times to equal resolution highpass subbands. threshold var an N 4 N for i N 4 N Decompose signal analytic filter bank of level 4 the variance of the two higher Examine the two highest resolution highpass subbands if an i threshold an i 0 end end sy synthesize1 an h0 4 figure fig2 plot t x k t sy-5 k axis xlabel Reconstruct original signal Plot signals Time sec Copyright Marcel Dekker Inc. All rights reserved. Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 TLFeBOOK 202 Chapter 7 The routines for the analysis and synthesis filter banks differ slightly from those used in Example in that they use circular convolution. In the analysis filter bank routine anaiysisi the data are first extended using the periodic or wraparound approach the initial points are added to the end of the original data sequence see Figure . This extension is the same length as the filter. After convolution these added points and the extra points generated by convolution are removed in a symmetrical fashion a number of points equal to the filter length are removed from the initial portion of the output and the remaining extra points are taken off the end. Only the code that is different from that shown in Example is shown below. In this code symmetric elimination of the additional points and downsampling are done in the same instruction. function an anaiyzei x h0 L for i 1 L a_ext an an 1 if Q. ipf conv a_ext h0 hpf conv a_ext hi ipfd ipf if 2 if ix-1 hpfd hpf if 2 if ix-1 Q. an 1 ix ipfdhpfd Ox Ox Ox Extend data for periodic convoiution .

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