Question about saving jpg file

Hi everyone,

I am doing a simple exercise of reading jpg file into Matlab
and writing it back to jpg file.

After writing the matrix to a new jpg file, the file size is
different. This is what I do:

A = imread('original.jpg');
imwrite(A, 'new.jpg', 'quality', 100);

The original jpg file is about 2 MB and the new jpg file is
about 3 MB.

I also tried this,

imwrite(A, 'new.jpg', 'quality', 75);

Now the new jpg is much smaller and about 500 kB.

So my question is that is it possible to write an image back
to file which is exactly identical to the original jpg file?

Thanks.
.

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