>20Mb JPG file - VERY grainy in iPhoto book

I recently made an 8 1/2 x 11 hardcover photo book in iPhoto, using the files given to me by my wedding photographer. When the book arrived, most of the prints were excellent. However, three (out of 90) were quite grainy. It looked as if they had been fed into Photoshop 3 and converted to 256 colors using a smart dither. Not grainy, so much as a very, very noticeable 256-color-seeming wandering dither. I went back to the original files I used to submit the album, and I noticed that, for whatever reason, the three "grainy" photos were all about 25Mb jpg files. The other 87 pictures, which were extremely clear, were all jpg files under 10Mb. I also noticed that when the album was sent to Apple upon creation, only about 86Mb was uploaded even though the pictures were all about 6-8 Mb apiece (other than The Big Three). So it would seem that when the book is being assembled, iPhoto is creating temporary down-sampled versions of the pictures on each page for upload. If you've got a JPG file that's too big, it would seem that it makes a very bad down-sampled image, which is then reflected on the printed page.

This first wedding book was for my mom. I've already ordered a second book for my wife's grandmother (I KNEW I should have waited for my mom's book to arrive first!). I'll try tinkering with the three 25Mb JPG files to get them down to 8Mb or so, and then put them in the book.

The upshot of the story is -- keep your JPG files well under 20Mb if you're going to include them in iPhoto print books!

BTW this was in iPhoto 2009.