Why the same data yielding different values?

Code:

abc=reshape( rate, size(CoverImage));

imageasbytes = typecast(abc(:), 'uint8');

imwrite(abc, 'exchan.jpg');

ss=imread('exchan.jpg');

imageasbytes2 = typecast(ss(:), 'uint8');

Both

imageasbytes2 and imageasbytes are giving different values inspite of the fact that I wrote that data ;

when i read the same file, values changed.

Why are they giving different values??

Answer 1

[Walter Roberson]

The JPEG image format uses lossy compression unless you specifically ask for lossless compression.