But, you've probably heard horror stories about saving in jpeg format and loosing detail in your photos. It's true that when you save a photo as a jpeg over and over again it'll being loosing detail. That's because each time it says "well, these pixels are close enough to record as the same color" it'll include more and more pixels in that "close enough" category, which means where there were details before, after a lot of re-saving, you'll eventually loose it.
So, how many times can you re-save a .jpeg file? It depends on how many pixels you have to start with. ("Megapixels" describe how many MILLIONS of pixels your camera has.) But, with my 8 Megapixel camera, I often convert my RAW files to jpg, then de-noise and save it as a jpg again, then edit it in Gimp and save it once or twice more. That's up to 4 times for those who are counting and I've yet to see any ill effects, either on-screen at 100% or printed at up to 14x11, so I think some people are a bit over-dramatic about how much you loose. Still, though, if you can save in a "non-lossy" format you should.
Alternatives -I save as .jpg because it's the only way I can retain my EXIF data, but it's definitely recommended that you save as TIFF or .png instead if you can. TIFF is much like RAW -the files are big, but they record everything pixel-by-pixel. On the other hand, .png files are smaller because they record blocks of the same color together to save space just like .jpegs. BUT! unlike .jpg's, they don't loose data by recording blocks of similar colors as "close enough" to be recorded as being the same color
So, to summarize, try to save your photos as .png or as TIFF's while editing, especially if you tend to save and re-save a lot. TIFF's are larger, so you may want to stick with .png's since they have the best of both worlds -they are smaller, but you don't loose any data when saving the file over and over again.
- Jpeg's do not loose quality each time they are opened. They only loose quality when they are re-saved.
- Saving a file under a new name each time will not prevent data loss.
- Saving a file under a new name will not cause data loss on the original file.
- Renaming a jpeg will not cause data loss.
- Saving jpeg's at 100% quality does not mean you won't loose any data (or detail), you just won't loose as much.