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how the compression ratio is calculated

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FIR
FIR on 24 Dec 2012
i have a code
X=imread(file);
wavelet='haar'
level=2;
[c,s] = wavedec2(X,2,wavelet);
alpha = 1.5; m = 2.7*prod(s(1,:));
[thr,nkeep] = wdcbm2(c,s,alpha,m)
[xd,cxd,sxd,perf0,perfl2] = wdencmp('lvd',c,s,wname,n,thr,'h');
disp('Compression Ratio');disp(perf0);
the size of xd and X is same,plz tell how compression ratio is calculated
both images look like same ,how we can say it is compressed ny 84%
perf0 is 84%

Accepted Answer

Wayne King
Wayne King on 24 Dec 2012
perf0 is the percentage of zeros in the wavelet coefficients. So 84% indicates that 84 percent of the wavelet coefficients have been set to 0.
perfl2 is the ratio (as a percentage) between the L2 norm of the compressed wavelet coefficients and the original (before compression) wavelet coefficients.
Yes, the output compressed image is of course the same size as the input, the point is that it is constructed from a much smaller set of wavelet coefficients
  5 Comments
FIR
FIR on 24 Dec 2012
Wayne i sthere any compression that can make the image into smaller size, as of 3 to 4 lines as above,i tried huffman but matlab crashes

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