Lossless JPG editor?

Does anyone know of a freeware lossless JPG editor? I need to do a little more than rotating.

Lossless? You re-save a JPG and you only lose more quality. To not lose even more quality after editing it, you'd have to save in PNG.

Though due to it having previously been in JPG the image would be littered with many tiny artifacts, which would bloat the PNG filesize.

http://en.wikipedia.org/wiki/Lossless_JPEG

There is no such thing as a lossless JPEG editor, since JPEG uses a lossy compression algorithm. The solution is to save to PNG to prevent further loss (and lose any compression savings the JPEG format had), or max the JPEG compression quality settings and hope it doesn't hurt the image too much. I stand corrected, lolwhoops. How does it compare to PNG?

Now, as far as freeware editors that do a "little more than rotating", there's Paint.NET or GIMP (if the format doesn't open initially, there are plugins out there). I prefer Photoshop, but it's not exactly free, durr.

Well, I don't know how accurate their claims are, but BetterJPEG claims it can, for example, losslessly crop a JPG image, which doesn't sound too far-fetched, given that mp3DirectCut can do similar things to MP3s.

However, I'm looking for something freeware..

I think he is referring to some software that does lossless transformation on JPEG, like the JPEG rotation some apps have integrated (which doesn't decode anything but transforms the encoded data).

As far as I know the algorithms behind JPEG there should be some more lossless operations you can perform on the picture data (because of the block-based structure). But it strongly depends on what you want to do.
And I doubt there is a lot of software out there that will do this kind of transformation for you.

You could try using the jpeglib yourself (I you can code), but I suspect this could be overkill...

If you're going to be editing a picture, don't do it in JPG. Convert it to a lossless format (Photoshop or GIMP's in-house formats, PNG, whatever), do all your editing, and then save it as a JPG. Preferrably start from a RAW image from your camera, so you only have to convert to a lossy format once.