Why imwrite compressed same size mat with different entropy to the same size (16bits)

For example there are two matrix which are the same size, but one are all zeros another isn't, when i try to compress them use imwrite with jp2, the result file size are the same. some times The mattrix are 16bit int.

[Walter Roberson]

I do not know, but I find this interesting remark at http://jpeg2000wellcomelibrary.blogspot.ca/2010/08/as-result-of-our-decision-to-go-lossy.html

"An interesting point to make about the very high experimental compression rates of 25:1 and above, was that output file sizes were essentially homogeneous across all the images, where as at 10:1 and lower, file sizes ranged from 1.5 Mb to 11.5 Mb."

What compression ratio were you requesting?

Answer 1

[Vidya Viswanathan]

I was unable to reproduce the behavior you described. I used the following code snippet to generate two images and save it in "jp2" format.

I=zeros([640 480]);
I2=rand([640 480]);
imwrite(I,'fig1.jp2');
imwrite(I2,'fig2.jp2');

This uses a default compression ratio of 1. The resultant images had significantly different sizes. The first one was just 1KB whereas "fig2" was of size 326 KB. Hence, I believe that this behavior is not consistent. Could you share the data for which you are observing this behavior?