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 62474 19054 ns/op 4218 B/op 188 allocs/op
BenchmarkDecodeCompareWithGoexif/bep/imagemeta/exif/jpeg/orientation-10 309145 3723 ns/op 352 B/op 8 allocs/op
BenchmarkDecodeCompareWithGoexif/rwcarlsen/goexif/exif/jpg/alltags-10 21987 50195 ns/op 175548 B/op 812 allocs/opLooking at some more extensive tests, testing different image formats and tag sources, we see that the current XMP implementation leaves a lot to be desired (you can provide your own XMP handler if you want).
BenchmarkDecode/png/exif-10 39164 30783 ns/op 4231 B/op 189 allocs/op
BenchmarkDecode/png/all-10 5617 206111 ns/op 48611 B/op 310 allocs/op
BenchmarkDecode/webp/all-10 3069 379637 ns/op 144181 B/op 2450 allocs/op
BenchmarkDecode/webp/xmp-10 3291 359133 ns/op 139991 B/op 2265 allocs/op
BenchmarkDecode/webp/exif-10 47028 25788 ns/op 4255 B/op 191 allocs/op
BenchmarkDecode/jpg/exif-10 58701 20216 ns/op 4223 B/op 188 allocs/op
BenchmarkDecode/jpg/iptc-10 135777 8725 ns/op 1562 B/op 80 allocs/op
BenchmarkDecode/jpg/iptc/category-10 215674 5393 ns/op 456 B/op 15 allocs/op
BenchmarkDecode/jpg/iptc/city-10 192067 6201 ns/op 553 B/op 17 allocs/op
BenchmarkDecode/jpg/xmp-10 3244 386336 ns/op 139861 B/op 2263 allocs/op
BenchmarkDecode/jpg/all-10 2874 389489 ns/op 145700 B/op 2523 allocs/op
BenchmarkDecode/tiff/exif-10 2065 566786 ns/op 214089 B/op 282 allocs/op
BenchmarkDecode/tiff/iptc-10 16761 71003 ns/op 2603 B/op 133 allocs/op
BenchmarkDecode/tiff/all-10 1267 933321 ns/op 356878 B/op 2668 allocs/opThe 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
HandleXMPoption) 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 ./genNote that you need a working exiftool and updated binary in your PATH for this to work. This was tested OK with:
exiftool -ver
12.76
Debuggin tips:
exiftool testdata/goexif_samples/has-lens-info.jpg -htmldump > dump.html