ezw_decode.m

EZW implementation which will use wavelet transforms and do the compression decompression using EZW

%*********************************%   

%*********EZW decoder*************%

%*********************************%

function ezw_decode_x=ezw_decode(X,LEVEL,DD,L1,SS,L2)
Y0=max(X);
Y1=max(Y0); %找到像素中最大值

%设最初门限制
     for i=0:20;
         if 2^i<=Y1 & 2^i>0.5*Y1;
             threshold=2^i;
             initialthreshold=threshold;
             laststeplevel=i+1;
             break;
         end;
     end;
     
global N;
[m,n]=size(N);     % the size of initial image, m is the pixels of initial image
XX=zeros(sqrt(m));      % initialize the reconstructured image to zero;
threshold=initialthreshold;    % initial theshold ;
sublist=[];       % sublist is the new position matrix for all significant coefficients 'p' and 'n';
f=min(laststeplevel,LEVEL);  
for level=1:f, 
    RR=zeros(size(XX));
    b=L1(level+1);
    
  % dominant pass
  i=1; j=1;
  while i<=m;
      if j>b; % b is the length of dominant pass vector
          break;
      end
      if RR(N(i,1),N(i,2))==1;
          i=i+1;
      else
          if DD(j+sum(L1(1:level)))=='p';
              XX(N(i,1),N(i,2))=threshold;
              RR(N(i,1),N(i,2))=1;
              sublist=[sublist;N(i,1),N(i,2)];
          end
          if DD(j+sum(L1(1:level)))=='n';
              XX(N(i,1),N(i,2))=-threshold;
              RR(N(i,1),N(i,2))=1;
              sublist=[sublist;N(i,1),N(i,2)];
          end
          if DD(j+sum(L1(1:level)))=='z';
              RR(N(i,1),N(i,2))=1;
          end
          if  DD(j+sum(L1(1:level)))=='t';
              RR(N(i,1),N(i,2))=1;
              RR=checkchildren(i,RR);% all zerotree's descendants are set to 1.
          end
          i=i+1;j=j+1;
      end
  end

  % subordinate pass
  [xx,yy]=size(sublist);
  threshold=threshold/2;
  for i=1:xx;
      if level==laststeplevel |threshold==0.5;
          break;
      end
      if SS(i+sum(L2(1:level)))==1;
          if  XX(sublist(i,1),sublist(i,2))>0;
              XX(sublist(i,1),sublist(i,2))= XX(sublist(i,1),sublist(i,2))+ threshold;
          else 
              XX(sublist(i,1),sublist(i,2))= XX(sublist(i,1),sublist(i,2))-threshold;
          end
      end
  end 
end 
ezw_decode_x=XX;