Focus points

Why ExifTool for Focus Points?

RawCull uses Apple’s ImageIO framework (CGImageSourceCopyPropertiesAtIndex) to extract standard EXIF metadata from Sony ARW files — shutter speed, aperture, ISO, focal length, lens model, and camera body are all read natively through Core Graphics. This works well because these fields follow the standard EXIF/TIFF specification.

Focus point data is different. Sony stores autofocus information — specifically the Sony:FocusLocation tag — deep inside a proprietary MakerNote block in the EXIF metadata. Apple’s ImageIO treats MakerNote as an opaque binary blob; it does not parse or expose vendor-specific tags within it. There is no kCGImageProperty key for Sony focus locations, and no Apple framework provides decoded access to this data.

ExifTool, by Phil Harvey, contains camera-vendor-specific parsers that understand Sony’s internal MakerNote structure and can decode FocusLocation into usable coordinates (sensor width, sensor height, x, y). RawCull reads a pre-generated JSON file produced by:

cd catalogARWfiles/
exiftool -Sony:FocusLocation *.ARW -j >> focuspoints.json

In the catalog where the ARW files are stored, the recommended procedure is to copy all ARW files to a temporary catalog before the culling process begins. Subsequently, execute the command provided within that catalog to generate the JSON file, which is automatically imported into RawCull if it exists in the catalog where the ARW files are stored.

RawCull is a sandboxed application, and executing the above command within it is prohibited due to restrictions. Consequently, it is necessary to execute the command and generate the JSON file outside of RawCull.

For the example picture (_DSC5220.ARW) the focus points extracted by ExifTool is:

...
{
  "SourceFile": "_DSC5219.ARW",
  "FocusLocation": "8640 5760 5292 2880"
},
{
  "SourceFile": "_DSC5220.ARW",
  "FocusLocation": "8640 5760 5778 2880"
},
{
  "SourceFile": "_DSC5221.ARW",
  "FocusLocation": "8640 5760 5548 2628"
},
...

This gives RawCull the focus point coordinates it needs to overlay AF point markers on thumbnails and zoomed views — something that simply isn’t possible using Apple’s default frameworks alone.

If the file focuspoints.json is present in the catalog for ARW files and contains valid focus points data, RawCull will notify the user of its existence, a yellow mark in the button row.