Originally posted by Peter Zack That's right. Anything you do to a Jpeg is destructive to the image. Even just a simple rotation from Landscape to portrait and then saving. But not if the image is RAW and you edit that way saving the final edited version to a Jpeg.
Wow, that's wrong in three ways! (EDIT: okay, two and a half.
)
1) 90°/180°/270° rotations to JPEG files can be done absolutely losslessly with a simple transform. However, it's true that if you do it within most image editors it won't be done without recompression. Use a tool which explicitly says it can do lossless JPEG rotation — if you're not sure, try
jhead.
2) if you rotate your RAW image at anything other than the "square" angles, it certainly does cause the loss I described before. (EDIT: obviously not to the original file unless you delete or overwrite that; sorry, I missed what you were saying on first read.)
3) And finally, saving your RAW to a final edited JPEG is of course a lossy step too. (But I suspect in many cases causing less
visible image degradation than #2.)