IPhoto changes my dpi while editing - what to do?

Question

Hello!
I have iPhoto 6 and have taken over 500 pictures for a wedding. Now they want to print bigger photos (A4) from my photos. All of a sudden we notice that all of the photos that I have taken with my Nikon D70, that are vertical have the dpi 70 instead of 300 needed for good quality print. Some of these pictures I have cropped but not all. I also have not turned all of them around. Most of them where taken the "right way" already with my camera. What I have done is that I have edited the colour or exposure in iPhoto. So why has iPhoto changed the dpi and why does it not ever notify me about this? Is there some way in how to prevent this from happening? Or change the dpi later in iPhoto? I can't possibly start re-editing each vertical photo in Photoshop, that is absurd! How can I prevent this from happening again?
Thank you for your help!

Answer 1

lkaranko:
Welcome to the Apple Discussions. The resolution has not been changed. It's the pixel dimension of the image that is the more important factor. If you take a 1600 x 1200 image at 72 dpi it will give you a 22" x 16.6" print. But if you take that same file and print at 300 dpi you'll get a 5.3 x 4" print.
iPhoto just reports the resolution at 72 dpi which, if printed at that resolution would give you a very large print. If you select a print size iPhoto will squeeze the available pixels into those dimensions. The smaller the print size the larger the resolution will be.
In rotating the files a new jpg file is created and when it's saved there will be some jpg compression applied. The original file is left intact and can be recovered by selecting the photo and using the Photo->Revert to Original menu option.
The bottom line is: as long as the number of pixels do not change (or by very much) the inherent resolution of the file is not changed.
Do you Twango?
TIP: For insurance against the iPhoto database corruption that many users have experienced I recommend making a backup copy of the Library6.iPhoto database file and keep it current. If problems crop up where iPhoto suddenly can't see any photos or thinks there are no photos in the library, replacing the working Library6.iPhoto file with the backup will often get the library back. By keeping it current I mean backup after each import and/or any serious editing or work on books, slideshows, calendars, cards, etc. That insures that if a problem pops up and you do need to replace the database file, you'll retain all those efforts. It doesn't take long to make the backup and it's good insurance.
I've written an Automator workflow application (requires Tiger), iPhoto dB File Backup, that will copy the selected Library6.iPhoto file from your iPhoto Library folder to the Pictures folder, replacing any previous version of it. You can download it at Toad's Cellar. Be sure to read the Read Me pdf file.