Though I shoot exclusively in RAW and edit all within the same Lightroom/Photoshop platform, at some point I end up saving my files to jpg. Whilst I’ve always understood that that first save to jpg inflicts some pixel damage to the image, I hadn’t fully appreciated that the loss of quality stacks with each subsequent save to jpg. A little while back, having been told about the effect, I thought I’d run a test – repeatedly saving, reloading and resaving a series of my images to jpg to see what happened.
The white figures indicate the number of repeated jpg saves.
At this scale the artifacts weren’t obvious for the first few saves. Seen at 100% or greater areas of the sky had become unacceptably degraded by as few as five saves, exhibiting the kind of level of damage seen at 10 saves in examples of this scale. The damage is a result of the jpg’s compressed nature. Keeping files in RAW, PSD or other non-compressed file formats will preserve quality and prevent this kind of degradation.