what is the compression ratio?? if i compare 'db' compression ratio with my designed filter..is it should be low or high to be efficient?

Answer 1

[Wayne King]

The compression ratio in the wavelet domain is usually expressed as the number of wavelet coefficients that are zero divided by the total number of wavelet coefficients.

This means that the closer the ratio is to 1, the better. If for some reason you're taking the log of that the the closer the log is to 0, the better.

You can use wdencmp() to obtain the compression score, the output argument PERF0.

[tamanna]

i use the code

 image2=('C:\Users\hp\Desktop\data\1 (2).JPG');
 wavemngr('del','josh');
 WAVEMNGR('add','shivjoshi','josh',1,'','newwavelet.m')
 OUT1 = WAVEMNGR('read') 
 [C,S] = wavedec2(image2,2,'josh');
 thr=1.0000;
 [Xcomp,CXC,LXC,PERF0,PERFL2] =wdencmp('gbl',C,S,'josh',2,thr,'h',1);

and compression ration i got is 0. Retained Energy is 100

PSNR value of decompressed image is 20.7744

and for 'db4' i used the code

 image=rgb2gray(imread('C:\Users\hp\Desktop\data\1 (2).jpg'));
 K=image;
% wavelet decomposition

 [C,S] = wavedec2(image,3,'db4');
thr=1.0000;
[Xcomp,CXC,LXC,PERF0,PERFL2] =wdencmp('gbl',C,S,'db4',2,thr,'h',1);

here The compression ratio is 55.0297

Retained Energy is 99.9997

PSNR value of decompressed image is 117.8089

is my designed filter better??

Answer 2

[Wayne King]

No, Unfortunately, the db4 wavelet filters is doing much better than yours.

A compression ratio of 0 means that none of the wavelet coefficients are being set to zero, which means you have no compression. That finding is backed up by the fact that you have retained all the energy. In compression you should not retain all the energy.

On the other hand, with the db4 wavelet filter, you have more than 1/2 the wavelet coefficients being set to zero.

[tamanna]

k..it means i need to work on my filters coefficient

one more question when i used this code

 image2=('C:\Users\hp\Desktop\data\1 (2).JPG');
  wavemngr('del','josh');
 WAVEMNGR('add','shivjoshi','josh',1,'','newwavelet.m')
 OUT1 = WAVEMNGR('read')
 [C,S] = wavedec2(image2,2,'josh');
 thr=1.0000;
 [Xcomp,CXC,LXC,PERF0,PERFL2] =wdencmp('gbl',C,S,'josh',2,thr,'h',1);

and put the value in function 'newwavelet' same as value of 'db4',i.e. [-0.0106 0.0329 0.0308 -0.1870 -0.0280 0.6309 0.7148 0.2304] i am getting different results. e.g. in this code, m getting

The compression ratio is 58.8000

Retained Energy is 99.9999

PSNR value of decompressed image is 91.1471

and in above 'db4' code, m getting

The compression ratio is 55.0297

Retained Energy is 99.9997

PSNR value of decompressed image is 117.8089

why the results are varying??