Writing is not supported, and never will.

I welcome PRs with fixes, but please raise an issue first if you want to add new features.

Extracting EXIF performs well, ref. the benhcmark below. Note that you can get a significant boost if you only need a subset of the fields (e.g. only the Orientation). The last line is with the library that Hugo used before it was replaced with this.

BenchmarkDecodeCompareWithGoexif/bep/imagemeta/exif/jpeg/alltags-10                68658             15825 ns/op            3034 B/op        128 allocs/op
BenchmarkDecodeCompareWithGoexif/bep/imagemeta/exif/jpeg/orientation-10           444249              2567 ns/op             501 B/op         11 allocs/op
BenchmarkDecodeCompareWithGoexif/rwcarlsen/goexif/exif/jpg/alltags-10              27206             44110 ns/op          141977 B/op        816 allocs/op

The output of this library is tested against exiftool -n -json. This means, for example, that:

• We use f-numbers and not APEX for aperture values.
• We use seconds and not APEX for shutter speed values.
• EXIF field definitions are fetched from this table: https://exiftool.org/TagNames/EXIF.html
• IPTC field definitions are fetched from this table: https://exiftool.org/TagNames/IPTC.html
• The XMP handling is currently very simple, you can supply your own XMP handler (see the HandleXMP option) if you need more.

There are some subtle differences in output:

• Exiftool prints rationale number arrays as space formatted strings with a format/precision that seems unnecessary hard to replicate, so we use strconv.FormatFloat(f, 'f', -1, 64) for these.

Many of the tests depends on generated golden files. To update these, run:

 go generate ./gen

Note that you need a working exiftool and identify(ImageMagick) in your PATH for this to work. This was tested OK with:

exiftool -ver
12.76

Debugging tips:

 exiftool testdata/goexif_samples/has-lens-info.jpg -htmldump > dump.html