The interface in Graphic Converter is rather confusing, and so is the manual. (I just did a search for “lossless” in it…) It sounds like there are two rotate functions, one “Rotate” that the manual claims is “performed lossless on JPEGs” and one “Rotate depending on EXIF” that is only available through a JPEG submenu in a contextual menu in some situations. It’s hard to tell: 1) what the difference between the two is; 2) how GC manages to avoid any loss of data when: decompressing a JPEG picture -> rotating it -> recompressing it as a JPEG.

I agree, however, that it’s not all that relevant for people who are willing to use JPEG in the first place. I must admit, however, that, while I use the highest quality JPEG format on my digital camera, whenever I open a picture to work on it, I save it as a TIFF in order to avoid any further loss of data.

I don’t know what the JPEG rotation technology in GraphicConverter is, but it certainly claims to be lossless. It’s a separate function that says “lossless JPEG rotation”. Hey, maybe it’s EXIF rotation! I really don’t know. I could go look it up, but I’m much too lazy for that.

However, I still stand behind my point: anyone who is satisfied with a JPEG in the first place really can’t complain too much about lossy JPEG rotation — “ooh, I’ve sacrificed another 0.2% of my image data after already sacrificing 25%!” Frankly, I would much rather accept the (imperceptible) data loss than deal with the (inevitable) confusion and bugginess that the EXIF rotation is already causing.

OTOH, a “lossless rotation algorithm” is impossible with JPEGs. As soon as you rotate a JPEG, the algorithm to save it has to start all over again. So there is additional loss every time you do this. I don’t know what Graphic Converter does, but I doubt that they have a way to avoid this.

Basically, the EXIF rotation idea is good, but it has to be implemented properly and consistently. But of course that assumes that the various departments at Apple actually communicate with each other and with third party developers.

First, this functionality should not be disguised as conventional rotation. If the image is not actually being altered, that’s relevant information that I want to have: I want a choice in the Preferences or the UI to rotate my pictures by method A or method B. Display-only rotation is a fundamentally different approach to the task, with obvious and significant consequences for rendering the image in a presumably large number of EXIF-stupid applications… including, apparently, Apple’s own Mail! Furthermore, there is the very real possibility that this discrepenancy will cause significant confusion down the road. Is it rotated or not? Easy enough to figure out what’s going on in the short term, but what about after the trail is cold? I might eventually open EXIF rotated images in an EXIF-stupid app (iPhoto, perhaps?!), not realizing that I’d rotated them in Preview long ago, and then actually rotate them… resulting in what? An image that has now been lossily/actually rotated but still also is EXIF-rotated, resulting in something that once again appears to be disoriented back in EXIF-smart applications? Agh! I don’t know if this would really happen, but it’s an example of the kind of unintended consequences in computing that result from trying to be clever without telling the user what the hell is really going on.

Second, why not simply implement a lossless rotation algorithm? They exist. The venerable Graphic Converter uses one. It’s possible that lossless rotation isn’t perfect (I don’t know enough about the technology to say), but anyone who is content with JPEG lossyness in the first place surely isn’t going to quibble about the difference between “just barely lossy” and “only a tiny bit more lossy”. Really, if you care so much about lossyness that whatever ridiculously small amount of lossyness occurs with a lossless rotation algorithm, shouldn’t you be using RAW files anyway? Surely, the convenience of creating actually rotated images and never facing an unrotated image in an EXIF-ignorant application

Okay, TIFFs are a different matter. But I refer you back to my first point. Give us a choice, Apple… unless you think it will be too complicated for us simple-minded consumers!

Anyway, the lack of support for the EXIF or “virtual” rotation in Mail must be a bug, even if the failure of rotation to be rendered in EXIF-stupid applications is not! All in all, I have to give this whole issue a triple eye roll and a deep, weary sigh. Obviously, it’s going to be a long time before I can rotate an image in Preview and have it stay politely rotated in Mail.

The other question: What does the rotation in iPhoto do? Does it use the EXIF approach or actually change the picture itself? If it uses the EXIF approach (as I hope it does), then how come Mail is able to show the picture with the correct orientation the second time around?

We still have unanswered questions here…

Just for future reference:
http://docs.info.apple.com/article.html?artnum=302669