Does Saving a JPEG Multiple Times Reduce Image Quality?

Click to enlarge. There is no noticeable difference in the two pictures even though there is clearly a theoretical difference.

This article is an in-depth explanation from my article “12 Photography Myths Every Photography Should Know.”

When photographers start debating the advantages of shooting RAW rather than JPEG, I inevitably hear that one advantage of shooting in RAW is that you can save it multiple times without reducing image quality.

In theory, this is absolutely true.  Every time a JPEG image is saved, compression algorithms are run to reduce the file size.  This means that some data is lost every time you make a change to the photo and save it.  In contrast, RAW is what is called a lossless format.  It makes no difference how many times you edit a RAW file, it will always contain the exact same data.

Even zoomed in to 100%, you can see that there is no difference in the quality of the photos.

Without any doubt, the RAW format offers clear advantages over shooting JPEG.  The most important of those advantages is the latitude to edit exposure and picture style.  The added information in a RAW file makes editing much more successful.

However, I often find that photographers take this too far and imagine that saving a JPEG multiple times is doing more harm that it actually is.  To see just exactly how much the pixels are altered buy saving a JPEG multiple times, I got one image and saved it out running compression on the image.  Then I painted one pixel white on the file just so it wouldn’t leave the file untouched, and then I took the resulting JPEG and repeated the process.  In all, I saved the original photo 30 times.

Even after saving the photo 30 times, I found no noticeable reduction in image quality.  None.

Granted, this test would certainly have turned out very differently if the test were performed while saving out lower quality JPEG images upon each save.  In my testing, I saved the photo out as the maximum quality JPEG to prove my point.  Clearly, this would not hold true if you save the photo in low quality.

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Comments from the I.P. Community

  1. says

    You don’t really say, but can we assume that each time you saved the file, you closed it, and then opened the previously saved file? Lather, Rinse, Repeat.

    Because, of course, if all you did was save the same image from memory 30 times you didn’t actually test anything.

    I also have to wonder what the effect would be of making broader changes to the file each time, rather than just 1 pixel.

    In general, I agree with you, though, that multiple saves don’t have a large impact on image quality if those saves are at low levels of compression (or High Quality, as Photoshop likes to say).

  2. says

    A more realistic test would be to make a small global change to the picture – like adjust exposure or contrast or whatever a tad – save and reopen and adjust back. Repeat this until the image degrades. Touching one pixel will change the area around it after compression, but the change will be mostly confined to the area around that single pixel, given the way the compression algorithm works.

  3. says

    “In my testing, I saved the photo out as the maximum quality JPEG to prove my point”

    Duh, if the image is being saved at maximum quality (i.e. no compression) each time then no information is being lost. What are you trying to prove?

    The default settings of most photo editing programs have the JPG quality between 90% and 95% – so for Joe Public the story about repeated saves meaning a loss of quality is not a myth.

  4. says

    You must have done something wrong. I took your comparison picture above, opened it in Photoshop, painted one white pixel, and saved it in JPEG format with maximum quality. I then closed it, opened it again, painted another white pixel in the exact same spot just to change the file, and repeated the process. I got tired after the 15th time, but by then the image had deteriorated noticeably. Have a look at the result:
    http://img827.imageshack.us/img827/7339/7bd7yegc15.jpg
    Here is the original image from the article:
    http://improvephotography.com/wp-content/uploads/2011/11/zoomManySaves.jpg

  5. says

    Victor: JPEG at maximum quality is not lossless.

    Martin: You did not make a global change, which is why there were no degradation.

    Look, guys (an this includes the writer of the article). None of this is news. Have a little faith in the experts. It was all explained 10 years ago in the JPEG FAQ: Multiple re-compressions at the same quality level and with local changes to the image does not degrade image quality. Global changes and/or changes to compression does.

    http://www.faqs.org/faqs/jpeg-faq/part1/section-10.html

  6. says

    Most of whatever you articulate is astonishingly legitimate and that makes me ponder the reason why I had not looked at this in this light before. This piece really did switch the light on for me as far as this subject goes. But at this time there is just one issue I am not too comfy with so while I try to reconcile that with the actual main idea of the position, permit me see exactly what all the rest of the readers have to say.Nicely done.

  7. says

    I can see that myth having it’s roots in the old days, when the Jpeg compression algorythm was not so advanced. i remember having my computer graphic and design courses around 2001 and being told that saving jpeg multiple times could give me quality loss… Nowaday, i’d be surprised to se any difference. Thanks for the infos though, cause i was still old-school !

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