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

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TIAN FENG
TIAN FENG 2016-1-29
关闭： MATLAB Answer Bot 2021-8-20
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.
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Walter Roberson
Walter Roberson 2016-1-29
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?

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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?

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