JPEG Original Exported By AE Differ From The True Original

A difference in file sizes between JPEG masters in Aperture and those exported by Aperture Exporter (AE) can occur for normal reasons, some unavoidable and others configurable.

Unavoidable Difference

Aperture may rewrite metadata within original files, including embedded preview icons. This produces smaller files than the original, though the image itself remains pixel-perfect.

Configurable Processing

AE performs additional processing on JPEG images to manage location data added in Aperture and orientation changes. When location metadata wasn't in the original file, AE recreates the image to include it, resulting in a new file size. While decompression and recompression cause minor fidelity loss, this is imperceptible in practice.

This extra processing can be disabled in advanced options, or XMP sidecar files can be created instead (though Lightroom won't read these for JPEGs).

Metadata Consideration

AE's processing may result in loss of camera-specific "Maker Notes" metadata, as OS X's Image I/O framework supports only a limited subset. Users can choose between retaining location data or preserving Maker Notes, or explore workarounds using XMP sidecars with external tools.

See also: Embedding XMP Sidecar metadata into JPEGs.