Title: Is compression lossless? Visual differences appear
Last modified: August 24, 2016

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# Is compression lossless? Visual differences appear

 *  Resolved [Lyk](https://wordpress.org/support/users/lyk-1/)
 * (@lyk-1)
 * [11 years, 1 month ago](https://wordpress.org/support/topic/is-compression-lossless-visual-differences-appear/)
 * Hello,
 * While I strongly appreciate the effort to keep providing for free part of your
   API, I had some weird results.
 * Smushing made the colors appear “washed-out” (as if brightness changes) in a 
   very obvious way.
 * I upload the photo 2 times. I smush the 1st and then compare with the 2nd. The
   smushed one appears brighter.
 * I see the same result with both Firefox and Chrome. Safari shows no difference
   between them(!)
    Saving the images from Firefox results in files looking the 
   same(!)
 * It is like Firefox and Chrome render the smushed image in some way that makes
   it look different(?!)
 * For the tests, I opened the online images directly (i.e. the .jpg files), so 
   no weird css could interfere or something.
 * Any clues? Never had issues with smushit or ewww optimizer before.
 * The tests were made on a retina MBP.
 * EDIT: Check on a non-retina device with firefox. Everything looks as expected(
   images looking exactly the same)
 * I am **really** confused…
 * [https://wordpress.org/plugins/wp-smushit/](https://wordpress.org/plugins/wp-smushit/)

Viewing 4 replies - 1 through 4 (of 4 total)

 *  Plugin Author [WPMU DEV – Your All-in-One WordPress Platform](https://wordpress.org/support/users/wpmudev/)
 * (@wpmudev)
 * [11 years, 1 month ago](https://wordpress.org/support/topic/is-compression-lossless-visual-differences-appear/#post-6016966)
 * Lossless is lossless. For jpg files we simply strip the meta and rearrange the
   compressed data (DCT coefficients), without ever fully decoding the image. Therefore,
   its transformations are lossless: there is no image degradation at all. We also
   render progressive if that improves size.
 * It sounds like something specific to your system (and maybe retina display) that
   is rendering the image different for you. Maybe you could give us a link to your
   original file so we can try to recreate?
 *  Thread Starter [Lyk](https://wordpress.org/support/users/lyk-1/)
 * (@lyk-1)
 * [11 years, 1 month ago](https://wordpress.org/support/topic/is-compression-lossless-visual-differences-appear/#post-6016988)
 * Thanks for replying.
 * Yeap, I agree with what lossless is, that’s why I wrote
 * > It is like Firefox and Chrome render the smushed image in some way that makes
   > it look different(?!)
 * Moreover, I mentioned that saving the images and checking them, proves that the
   images are indeed identical visually.
 * It has to be an issue with the Firefox, Chrome jpg rendering on retinas or something.
   It may worth some further investigations and maybe a report to the firefox/chrome
   teams.
 * I used the Medium 640 image from here [http://foter.com/photo/abandoned-buildings/](http://foter.com/photo/abandoned-buildings/)
 * [Here](http://imgur.com/IFw6OGL) is a split view (via a screenshot) of the differences
   between smushed and non-smushed images, as they are presented by firefox
 *  [Aaron Edwards](https://wordpress.org/support/users/uglyrobot/)
 * (@uglyrobot)
 * [11 years ago](https://wordpress.org/support/topic/is-compression-lossless-visual-differences-appear/#post-6017060)
 * I can see the same thing, but the diff is a lot more minor than it sounds like.
   Lossy does the same thing. I’d have to leave it at something to do with the original
   encoding.
 *  Thread Starter [Lyk](https://wordpress.org/support/users/lyk-1/)
 * (@lyk-1)
 * [11 years ago](https://wordpress.org/support/topic/is-compression-lossless-visual-differences-appear/#post-6017061)
 * I guess you mean on a retina screen right?
 * I initially noticed the issue with other, normal images of my blog. (images from
   dslr)
 * It is not a huge difference, but I randomly noticed when I saw a picture of a
   person being noticeably washed out. Then I started testing.
 * I guess the original encoding has nothing to do, since the original pic -when
   uploaded- looks as expected

Viewing 4 replies - 1 through 4 (of 4 total)

The topic ‘Is compression lossless? Visual differences appear’ is closed to new 
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 * 4 replies
 * 3 participants
 * Last reply from: [Lyk](https://wordpress.org/support/users/lyk-1/)
 * Last activity: [11 years ago](https://wordpress.org/support/topic/is-compression-lossless-visual-differences-appear/#post-6017061)
 * Status: resolved