how the compression ratio is calculated

FIR
2012 12 24
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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%

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Wayne King
Wayne King 2012-12-24

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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

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FIR
FIR 2012-12-24
so can we tell that the image is compressed to 84%
Wayne King
Wayne King 2012-12-24
yes, by that metric
FIR
FIR 2012-12-24
编辑：FIR 2012-12-24
nnz(perf0) gives as 1
Wayne i sthere any compression that can make the image into smaller size,the code used me as of 3 to 4 lines as above,
Wayne King
Wayne King 2012-12-24
perf0 is just a scalar, so why would you use nnz() on that and expect something other than a 1?
FIR
FIR 2012-12-24
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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