About every seven minutes a question comes up on the Apple Aperture support forum that boils down to "How do I put text on images using Aperture". If I happen to see it I usually will try to walk the poor hapless victim through using the Aperture book feature to do it. I felt it might be useful for me to do that here for a couple of reasons. The first being - putting text on images with Aperture, the second and probably more important is perhaps getting people to think outside the box regarding how you might wire together a couple of Aperture's features to suit your own needs. Third - I love the book feature.
Let's say the task at hand is to put some of your hard won metadata that you have like captions on a bunch of images that will end up as JPGs posted on the web or sent out via email or something like that. Not really a book at all. Start by creating a new empty book with a custom theme. I happened to specify a page size of 8in by 12in so that the aspect ratio would fit my 3:2 DSLR images with no border. I also zeroed out all the margins so that there would be no binding offset.
Next I got rid of most of the pages that Aperture will generate for your new custom theme and clicked on the "Edit Layout" button on one of the pages that were left. I added a metadata text box, mine defaulted to caption, if you would like to put different metadata on the page make sure that the appropriate text box is selected and choose the metadata field you want from the drop-down menu.
Before going back to the "Edit Content" book view save your shiny new page with full bleed image and text box to a new master page using the little gear box drop down in the lower left area.
A great idea at this point is to use that same little gear box menu to "show master pages" and rename your page to something intelligent or at least something that you will remember what it does.
As many may already know and I continue to harp on about - Aperture does not save all this stuff in the "custom theme" it exists only in the actual book that you created the new master page in. Not a big deal but you do have to be pretty organized about where and when you change page layouts and save them as master pages to reuse. If you have pages in different instances of books it is nearly impossible to put them together again without redoing the layout work or something just as time consuming. I do all my custom page layouts in one instance of a book that I keep in a blue folder containing all the book themes, sizes, and layouts that I have modified over time. When I need a new book I just go to that folder, duplicate the book that has exactly the page layouts I want, and drag it into the project where it will be used.
Getting down to business let's use the new book with the new custom page layout. Just duplicate it, drag it to a project that has the images with the captions that you need, select the images that you would like and drag them into the book. Technically you do not need to drag the book anywhere special but to stay organized it's better to do it now than have a bunch of stuff laying around where it doesn't belong.
Here is a nice little short cut that even the Aperture book initiated might benefit from. Inside of the book select all of the images targeted to have their captions emblazoned on the front of them. Remember the "Show master pages" where we renamed our custom page layout? Make sure that it is displayed and select that page. Down on the lower right hand side choose "Add New Pages From Master"->"With Selected Images". Aperture will put all of those selected images in a new pages using the master page of your choice. This is a real time saver if you have a book or page layout library that fits what products you have to deliver. You can of course use it to generate all types of pages using various selections and then rearrange the pages by dragging them around.
The last step is to render the book to images. Choose File->Print book. From the wondrous little PDF menu in the print dialog you will probably want something like "Save PDF to Aperture" or choose one that suits your purposes. You can even make new ones that do exactly what you want, checkout an earlier article in the series for details. "Save PDF to Aperture" is a pretty cool one because at the end it shows you a dialog with a bunch of options for image format, where to put the images in your library, etc. Once the images are in your library with the captions you can publish them to a web journal, mobile me, export them using a plug-in to flickr, whatever. You get the idea.
Hopefully this gives you some new ideas about how you might be able to use the Aperture book feature to make you life a little bit easier or do something you might not have thought about before.
Of course you could just use something like the free BorderFX plug-in here, to do something like this but that would take all the fun out of it.