Redundant Wavelet Transform - Sparse Image and Signal Processing - page 71

% Estimate noise std from diagonal band at finest scale.
hh = uwc(2*N+1:3*N,:);
sigma = MAD(hh(:));

% Hard-threshold UWT coeffs: finest scale at 4*sigma
% and other scales at 3*sigma.
% Finest:
uwc(1:3*N,:)

= HardThresh(uwc(1:3*N,:),4*sigma);

% Other scales:
uwc(3*N+1:end-N,:) = HardThresh(uwc(3*N+1:end-N,:),3*sigma);

% Hard-threshold DWT coeffs:
ll = wc(1:coarsest,1:coarsest);
% Finest vertical:
wc(N/2+1:N,1:N/2) = HardThresh(wc(N/2+1:N,1:N/2),4*sigma);

% Finest horizontal:
wc(1:N/2,N/2+1:N) = HardThresh(wc(1:N/2,N/2+1:N),4*sigma);

% Finest diagonal:
wc(N/2+1:N,N/2+1:N) = HardThresh(wc(N/2+1:N,N/2+1:N),4*sigma);
% Other scales:
wc(1:N/2,1:N/2) = HardThresh(wc(1:N/2,1:N/2),3*sigma);
wc(1:coarsest,1:coarsest) = ll;

% Reconstruct.
imdenuwt = IWT2_TI(uwc,coarsest,qmf);
imdendwt = IWT2_PO(wc,coarsest,qmf);

% Display.
subplot(221)
imagesc(img);axis image;axis off
set(gca,'FontSize',14);
title('(a)');
subplot(222)
imagesc(imn);axis image;axis off
set(gca,'FontSize',14);
title('(b)');
subplot(223)
imagesc(imdenuwt);axis image;axis off
set(gca,'FontSize',14);
title('(c)');
subplot(224)
imagesc(imdendwt);axis image;axis off
set(gca,'FontSize',14);
title('(d)');
colormap('gray')