XMP Sidecar files can optionally be generated for JPEGs via an advanced option. While there are many advantages to storing metadata in these sidecar files there is one big drawback. Adobe's Lightroom does not read them for JPEGs.

This is typically not an issue as in its default configuration Aperture Exporter embeds metadata directly into JPEGs. This approach works well in most situations for most people using most cameras. However, when issues do arise it becomes most apparent when examining the "originals" that were exported via AE and the "originals" that are either referenced or managed by Aperture. For details about what can go wrong see our support page entitled JPEG Original Exported By AE Differ From The True Original. Note that this issue is not limited to AE. It is also a problem when using Aperture's built in feature that Writes IPTC Metadata To Original.

The following describes a method of ensuring that the maximum amount of metadata is retained from the true "original" while merging in other metadata added or modified in Aperture is also retained. In summary you will configure Aperture Exporter to generate XMP Sidecars for JPEGs in advanced options. Now go ahead and export your images using Aperture Exporter.

In the next step we will take the XMP Sidecars and embed their metadata back into the JPEGs, thus making it compatible with Lightroom. This will require the use of a command line tool called exiftool.

ExifTool is a platform-independent Perl library plus a command-line application for reading, writing and editing meta information in a wide variety of files. ExifTool supports many different metadata formats including EXIF, GPS, IPTC, XMP, JFIF, GeoTIFF, ICC Profile, Photoshop IRB, FlashPix, AFCP and ID3, as well as the maker notes of many digital cameras by Canon, Casio, FLIR, FujiFilm, GE, HP, JVC/Victor, Kodak, Leaf, Minolta/Konica-Minolta, Nikon, Nintendo, Olympus/Epson, Panasonic/Leica, Pentax/Asahi, Phase One, Reconyx, Ricoh, Samsung, Sanyo, Sigma/Foveon and Sony.

It is freely available from http://owl.phy.queensu.ca/~phil/exiftool/

I've done some work with exiftool looking for an easy workflow to ingest the XMP sidecars into the JPEGs. It is very feasible. To do so I do the following:

  1. Backup the folder to which you exported your Aperture library. You might consider this to be optional because if something goes wrong you could always perform another export using AE.
  2. Open terminal.app

  3. Use the following command in terminal.app

    exiftool -overwrite_original -tagsfromfile %d%f.XMP -all:all -ext jpg -ext JPG -r DIR

    Where DIR is the root directory you want exiftool to start working on. For example: /path/to/your/AE_EXPORT_DIR

    This command line tells exiftool to process all the JPEG images in the exported folder and subfolders. It will read the metadata in an XMP sidecar, then write it to the metadata structure of the JPEG. Note that this does not affect the image itself, so you don't need to worry about loss due to recompression. In my experiments this provided excellent results, maintaining the existing metadata and adding/modifying the metadata as reflected in the XMP sidecar.

    Let me know if you try this tip out and if it works out well for you.