Among Mac users, Apple’s iPhoto for Mac is a very popular tool for storing and managing photographs: it’s easy to use, has a pretty decent set of features, and it comes bundled with every Mac.

However, it does have some quirks, and one in particular can have quite an impact if you are shooting high-quality photographs such as the TIFFs or MAX-quality JPEGs produced by 645 PRO.

You might think that when you import your photos into iPhoto—either directly from your iPhone’s Camera Roll or a folder on your Mac—that iPhoto simply places a straight copy of the original file in its Library. And, sometimes, you’d be right—but not always.

Sometimes the image you see in your iPhoto Library is the original image, copied straight across. On other occasions, however, the image has been modified by iPhoto before being re-saved (always as a JPEG, whatever the original format). To see this in action, we’ll import two TIFF images taken with 645 PRO and saved to Camera Roll. The first image is in landscape format (wider than it is tall) and the second in portrait (taller than it is wide).

Once the import has been completed, we’ll select the landscape image and click the Info button at the bottom of the window. What we see is what we’d expect to see:

We have a TIFF file that’s 7.5 MB in size (when 645 PRO saves TIFFs to Camera Roll it compresses them from their original 24 MB using the lossless LZW algorithm). Now let’s take a look at the info for the portrait image:

What’s going on here? The TIFF has turned into a JPEG of one-third the size! This means its been through quite a bit of lossy JPEG compression, as well as changing format.

It seems that iPhoto is very picky about the specifications of the files it stores in its Library. If an image doesn’t quite meet those specifications (whatever they may be), iPhoto “fixes” it and then saves the modified file as a JPEG with Apple’s standard level of compression.

However, all is not lost (it’s just very well hidden). While iPhoto’s own Library contains this modified image, iPhoto has actually copied and saved the original too. To find it, select the File menu and then Reveal in Finder. If the file has been modified by iPhoto you’ll be able to choose whether to reveal the original or the modified file. Select Original File to open up a Finder window with your unmodified file selected, ready for you to open it in an editor that—unlike iPhoto—will only change your image when you tell it to.

Note: check ALL files!

It’s important to note that iPhoto doesn’t just modify portrait-oriented TIFFs from 645 PRO. It sometimes even changes landscape-format JPEGs, and it changes images from other apps and digital cameras too. If you’re putting the effort into maximizing the quality of the images you take, it’s an idiosyncrasy worth knowing about!