Thank you to Robert Watcher of finchandchimps and Robert Watcher Photography for this interesting guest post answering the question, “Does opening and resaving jpeg images over and over really degrade the image quality of your photos?”
I have long been fascinated with the claim that resaving your images files will degrade the image. Even with a simple file name change and resave as Jpeg there will be a generation of degradation. Now I am not disputing that that is what takes place – – – but what I have taken notice of is the feeling by most photographers that they cannot resave as a jpeg or else they will end up with a blocky unusable image.
Well several years ago, I did a test by opening and resaving a jpeg file without doing any processing in between, and saving again at the highest quality. Contrary to what I had been led to believe (that opening and saving even once or twice would be detrimental), there was not a significant degrading of the image I was using where I wouldn’t be able to use or recognize the image or print a good quality of print – even after opening and resaving I believe it was 20 times before I started noticing serious degrading particularly in sky areas.
So my conclusion back then as it is today – is that we needn’t worry excessively about resaving a few times at the highest jpeg quality. How much one could resave of course would depend on the image content and the application. In most cases however, we generally would go back to the original image file to keep doing extensive changes instead of opening and processing and saving as jpeg over and over again.
How I personally do it with my jpeg files from the camera (same if I used raw for that matter) is to save my processed image files as .psd or .bmp or some other lossless file format and then there is really not an issue with degradation as I continue to reprocess and resave. But if necessary, I would not hesitate to resave even as a high quality jpeg – and have done so many times where I have saved a processed file as a jpeg for printing and later wanted to tweak things a little without starting fresh.
So I thought that I would revisit this test that I did those many years ago – and decided to use a file from my Olympus E-3 that contained a variety of subject matter – but importantly I wanted an image that would also include large smooth blue sky areas which are the type of content that shows break up of the image and compression artifacts most significantly. My process was to to open the original jpeg file and Rename the file while saving as a Jpeg quality “12” and then close the file in Photoshop. I then reopened the newly saved file and Renamed the file while saving as a Jpeg quality “12” and then closed that file in Photoshop. I repeated this Open/Save/Close process to build up the number of generations.
This is the original file image:
And this is the 10’th generation image after resaving as Jpeg quality 12 in Photoshop:
For all practical purposes, even with this extreme number of resaves, the 10’th generation could still be used for web and print, although I doubt that anyone would need to resave 3 or 4 times let alone 10 or more times.
I have taken a 100% crop from the original file, 5’th generation file, and 10’th generation file for comparison, and resaved them for the web at 100% quality to make the comparison more accurate.
600×450 pixel crop from Original file:
600×450 pixel crop from 5’th generation file:
600×450 pixel crop from 10’th generation file:
There is no doubt that smooth sky areas begin to show the effects of jpeg compression by resaving over and over, but they are the worst hit (that is why I included them in my test image) and even with this file would likely only be noticed when viewing 100% on a monitor and not when printing or resizing for use on the web (the most common applications). Other areas of the scene however, show far less if any degrading even after many saves. My purpose again is not to say that resaving many times as a jpeg file is the ideal thing to do. But by testing with ones own content and application, it may not be nearly as big an issue as many make it out to be – and may even prove practical the odd time when needed.