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TechBusters: Saving as JPEG lowers quality.

Sunday, August 26th, 2012 by | Filed Under: Digital Photography
 
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Welcome to TechBusters from WorldStart, where I expose the truth behind technology myths and sayings.

In this article I’ll talk about the popular saying that if you save your images as JPEG over and over you’ll be lowering the image quality by a lot. This saying comes from the way jpegs compress the file. Each time you save a file the compression recalculates and the theory is after a lot of saves the file will be of noticeably inferior quality.

Let’s clear up one incorrect myth right off the bat: Opening the file does nothing to the image, so if you always open the original image file then save any edits as a new file the original image will not change. Only saving the file engages any changes/compression of the file.

So is this myth true? Let’s start by saying if you save at a low quality setting then you will produce low quality jpeg, so we’re going to test it with a medium-high quality of 70 percent. I tested this by starting with a high resolution 16 megapixel image converted from a RAW image file from a Nikon D7000 dSLR. I then proceeded to save this image 5, 15 and 25 times (opening and closing the image each time) and made 100% crops of an area of the image. Each save is at 70% quality jpeg (7/10 setting.)

Here is the re-sized full images of all 4 stages of the saving process.

Here are 100% views of a 300×450 area to compare the 4 stages of saving. This would be the equivalent of printing this image at 11×17 inches at 300 DPI.

Can you tell a difference from one to the other? I can’t. Is there a theoretical loss of information and jpeg artifacts introduced with each save you make? Yes. Do I think there is a visible difference in the image quality for the average person who may save an image a few times over? No way!

But like beauty maybe the truth of this myth is in the eye of the beholder – so you be the judge.

~Tim

 

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5 Responses to “TechBusters: Saving as JPEG lowers quality.”

  1. Jeff says:

    I’m not sure if you missed the point of this myth because you were not clear what you were saving. The myth states if you open file A.jpg, edit as you would like and save it to B.jpg (without resaving A.jpg) then A.jpg is never changed. This is true. Just like opening a word document and saving it as a new file doesn’t change the original file. You can look at dates and file sizes to check this myth as well. If you are going to make changes to an image it is always best to save it as a new file name before making any edits in case you accidently click Save and overwrite the original. Your example sounds like you are testing the degradation due to repeated jpeg compression.

  2. Hello, just wanted to say, I liked this article.
    It was practical. Keep on posting!

  3. Mike Loucks says:

    Thank you for clearing up a myth or two about jpeps!

  4. PWT says:

    I’m a photographer. I publish hundreds of shots each year in extremely high quality magazines for one of the world’s biggest publishing houses. At one stage I was having somewhere between 1000 and 1500 images pass across newsstands annually. If you’re worried about image degradation then save at the 100% quality setting in whatever program you’re using; you’ll never have a problem. Also, if you’re manipulating an image, save your work in the native file type of whatever program you’re using as your work progresses. Then, when you’ve finished editing, save it as a jpg. You’ll find that it’s probably bigger than the original image. If you work to these standards you will not have any problems. And don’t get me started on RAW.

  5. Nick says:

    I’m not certain about what you did. Did you make 25 separate copies of the original image, or did you make a copy of a copy of a copy, etc.? The latter process would be very interesting, and I hope you’ll give us a demonstration in your newsletter.

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