3

This isn't a problem I'm currently facing, rather just a curious thought.

I know that every time you open and resave a jpeg it will lose information, How many time could you do this until there is a noticeable difference? 10/100/1000 times?

  • 2
    define 'noticeable'? I guess this is really dependent upon the kind of image you're using. A photograph of eg. a person would suffer way less than, say, those marriage equality equals signs a couple years hence. – Vincent Mar 17 '15 at 12:26
  • @Vincent Well as it was just a thought I can't really define. Let's say portrait photo; roughly how many times could you resave until you looked at them side by side and know that the quality has dropped. – SaturnsEye Mar 17 '15 at 12:29
  • 3
    If you have a good enough display and eyesight, once. – Ilmari Karonen Mar 17 '15 at 14:00
  • This reminds me of a technique in audio signal processing called "noise floor distortion", whereby an audio signal is repeatedly attenuated and amplified back to original volume. It yields some interesting effects :) – MattDavey Mar 17 '15 at 19:49
7

I've seen a video featuring this. I'm not sure what it was anymore, but check out these 3 videos (from YouTube and Vimeo):

(The images aren't hyperlinked. Instead, there are linked texts at the bottom of each.)

Jpeg degradation by Connecticut State Library
1-Jpeg degradation by Connecticut State Library

JPG artifact test 1000 saves by Martin Flucka
2-JPG artifact test 1000 saves by Martin Flucka

Generation Loss by hadto
3-Generation Loss by hadto This last one by hadto on Vimeo also has a code (for the programming language "Processing") to achieve the same. http://hadto.net/sketchbook/generation-loss/

I'm sure there are more out there.

  • Thank you! a clear indication of how an images lowers quality – SaturnsEye Mar 17 '15 at 12:57
  • You're welcome @SaturnsEye :) Just sharing what others have done. – Lorgen GR Magpantay Mar 19 '15 at 19:52
7

There is no simple answer - each compression event dumps some data, it tends to dump less with subsequent saves as most of the disposable data has already been disposed of. Factors include the compression level, the size of the image, it's content, your personal threshold of "noticeable" and the quality of your monitor.

0

I once worked for a multimedia company where a graphic-artist was tasked with this exact question. Her findings were:

  1. A jpeg can be compressed up to 1/10 of the original bitmap (bmp) without any distinguishable* changes.
  2. Such a jpeg can be re-saved up to three times at the same compression level, without any distinguishable* artifacts.

*distinguishable: to a 'normal' 'regular' human viewer, without magnifying the image.

0

It depends...

  • on the image
  • the resolution of the image
  • the software saving the JPG
  • the amount of compression you are using on the JPG
  • the opinion of the person looking at the image

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