I had a bit of a 'light bulb' moment yesterday in my endeavours to migrate my back-catalogue of photos from Lightroom (LR) to Aperture, and I thought I would share here, in case anybody else is trying to do the same thing as me.
When I decided to make the switch from LR to Aperture, my immediate concern was how to migrate the image collection I had built up in LR over to Aperture. I had already decided that I wanted only one archive moving forward, but I had a stack of photos from 2010 (when I bought my first SLR) up to 2012 that needed to be moved. Since mid-2011 I have shot almost exclusively in RAW, so for every image I have a RAW master version, and a JPEG 'final' version, including all of the adjustments I made in LR.
The adjustments made in LR cannot be converted into Aperture adjustments, and vice-versa. When I started out with my archiving, I thought that the best I could do would be to import the RAW file and its corresponding JPEG edit as two separate images, and link them together in Aperture using Stacks.
However, Aperture does have a much neater way to import RAW+JPEG 'pairs'. The option can be found in the Import Dialog (see image). I believe it was originally intended for photographers who use the dual RAW+JPEG capture mode in their camera when taking photos, but it works just as well for this purpose too.
You will need to save a JPEG copy of each of your RAW images in LR, which includes all of the adjustments you have made. This JPEG must reside in the same folder on your hard drive as the original RAW file (for some reason, if it resides in a different folder then this process doesn't work).
Using this option means that your RAWs and JPEGs are linked together in Aperture, and will retain any metadata changes that you made in LR. If you make additional metadata changes in Aperture (for example, you add a new keyword), that will be applied to both versions simultaneously. Aperture treats the pair like it does any other master/version pairing.
This is not an article about why you should choose Aperture over LR, or vice-versa. I have tried both programs. I used to use LR on my Windows laptop, but about a year ago I bought a Mac and at that time I decided to give Aperture a try. I found I liked it, it works great for me and my workflow, and I have been using Aperture ever since, to catalogue, develop and export my images. The tide of opinion at the moment does seem to be very much in LR's favour, but for those who are contemplating Aperture, here is an excellent article on the benefits of Aperture over LR.