difference in compression ratio for same wname..

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 when 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);

, 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??

Answer 1

[Wayne King]

I get exactly the same. Can you try to reproduce with an image from MATLAB

    imdata = imread('ngc6543a.jpg');
    [C,S] = wavedec2(imdata,3,'josh');
    [C1,S1] = wavedec2(imdata,3,'db4');
    thr=1.0000;
    [Xcomp,CXC,LXC,PERF01,PERFL2] =wdencmp('gbl',C,S,'db4',2,thr,'h',1);
    [Xcomp,CXC,LXC,PERF02,PERFL2] =wdencmp('gbl',C,S,'josh',2,thr,'h',1);

I get 80.4151 for a compression score in both cases.

Perhaps you have entered the filter coefficients in your M-file without the full resolution that they are stored in MATLAB?