JPEG, TIFF, PSD, Successive Save, Save As, and more how?
There’s often confusion about what makes a JPEG and other files degrade, so I though it was time to do a real world test. First let me say that simply copying, or viewing a file does not cause any degradation as some believe. If you copy and paste a file it’s simply a bit for bit copy, and there’s no loss.
When you open, and then re-save a file is when things usually change. When you do this, even if you save at the highest quality JPEG settings you have still uncompressed the file, and it gets re-compressed when you save again. Unless or course your using an uncompressed file format to start with.
So how bad is a file damaged each time you successively save it. Well lets just say you should keep your originals folks. Below we’re going to look at the same image submitted to various torturous conditions. You can then judge for yourself.
Actual images were 700px wide. Click any version to see full size, or download all the images (plus a few extras) to compare them. Images that were opened and saved with “Save As” rather than “Save” commands are noted as such. If you want to join the discussion beyond comments here is the forum topic on this.
Original File.
Open / Save / Close / 100x
Here we simply opened the file and saved it again 100 times. No pixel edits were done to the image, we just made a type layer, and then deleted it so that PS would allow us to save. Apparently PS could tell that no pixels were edited and did not overwrite the unchanged pixels. Minimal or no degradation here.
Open / Edit / Save / Close /100x
To get results for actual pixel modifying edits we opened the file, added 5 brightness, saved, & closed. Then opened again, reduced 5 brightness, saved, & closed. Total 100 saves. We can see notable pix lossy degradation with this test.
Bright +5 / Bright- 5 / 100x
This is the same as above except that no save was made in between brighten 5, then darken 5. No loss in quality here. Just the brightness tool 100 times didn’t hurt the image. It’s seems saving kills those pixels, not the edit itself.
Resize / Revert 100x
Now admittedly most of us don’t do this but the test proved interesting. The 700px wide image was resized to 701, and then reverted to 700 . We did this 100 times. No save was done in between resizes. The huge quality loss is just from the resize and revert. Needless to say it’s hard on an image to resize it much. On the other hand we may have discovered a new aryistic effect!
Open / Save As / Close / 100x
No edit done here. We just did a Save As 100 times at the highest JPEG quality.
Results are pretty scary. 100 saves and the image is shot to pixels.
Open / Save As / Close / 25x
No edit done here either. We just did a Save As same as above but only 25 times. Even at 25 saves the image is pretty too bad to print.
PSD /Open / Save As / Close / 100x
So it’s clear that editing and re saving a JPEG is destructive. What about a PSD. We saved the orig JPEG as a PSD, then did open, and Save As & close 100 times. Little or no file degradation here. Obviously PSD is makes a larger file, but it does work well, and you can also save in layers. 
Tiff / LZW / Save As / Close / 100x
Tiff fared well. We did the Save As command 100 times using Tiffs LZW compression. Degradation was barley noticeable. Granted the file size came out about 2 times larger with Tiff, but quality stayed strong.
Conclusion.
It’s clear that saving in JPEG is destructive. Using the Save As command is especially hard on image quality. Granted one or two saves won;t trash your image, but degradation increases with each save sequence.
The bottom line is that we should always keep the original file. If you have an image you expect to be working on, and saving a lot of times them make it a PSD, or at least a Tiff and save the final edit from the that.
We also are aware there are other current file formats, as well as up and coming ones. What do you think is the best quality for the space? Or does space really matter anymore?
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Article & Children’s Photography by Gavin Seim
Wow - those are some scary results! I’m glad I shoot in RAW and use LR and PS to avoid this kind of thing. Having said that would I really open and save a jpeg 100 times?
It would also be interesting to see how the degradation evolved with the “save as…” and “resize” options. These were clearly the processes which generated the worst images, and if you had one picture which was “saved as” 10 times, one “saved as” 20 times, one “saved as” 30 times, etc. we could se if there was a critical point where an abrupt degradation ocurred or if the process degraded the picture linearly with only small changes from 10-fold to 10-fold “save as…” actions.
Thanks for testing this and sharing this. I was most surprised by the resizing by 1 pixel image.