Feb 16, '05 09:22:00AM • Contributed by: jaysoffian
When you import photos, iPhoto creates a thumbnail for each image. This thumbnail is 240 pixels wide by however many pixels high are appropriate to retain the original aspect ratio. You'll find these files in the iPhoto Library/YYYY/MM/DD/Thumbs folder, and you can open them in Preview to see their size. What I finally realized is that when you're in the Organize view of iPhoto, if you keep the photo size slider so that the images are no larger than the thumbnails (about 3/4ths of the way over), iPhoto is *much* faster than if you move the slider further over.
What I figure is that as long as you keep your displayed photos smaller than the thumbnails, iPhoto loads the thumbnail files and scales those down to the requested size. But as soon as you move the slider to larger than that, iPhoto has to load the original images and then scale them down in order to display the requested size. With the size of my library and my 6 megapixel images, this was causing my machine to start swapping like mad as iPhoto attempted to read in and scale all those images. Since the GUI slider isn't very precise, I played around with setting it to different values via the iPhoto preference file. e.g.:
defaults write com.apple.iphoto ThumbnailSize .80
Ideally you could set this to a value such that iPhoto wouldn't need to scale the thumbnails at all and could just display them as they are on disk, but I was unable to figure out the magic value. It's somewhere between .8495 and .85 though. On my machine, it's pretty obvious whether iPhoto is scaling from the thumbnail file or from the original image.
So anyway, with ThumbnailSize at .8495, iPhoto is fast enough that I'm happy even with my original library of 10k images. Your mileage may vary, of course.
[robg adds: A previous hint for speeding up iPhoto still seems to hold true in iPhoto5 -- get rid of the shadows.]
