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TechBusters: Saving as JPEG lowers quality.

Posted By Tim On August 26, 2012 @ 12:00 PM In Digital Photography | 5 Comments

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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