This all started out by trying to rapidly browse on a Mac the image files in the Photos application and turning them into jpeg files for later use in a web page.
The image files are stored in various subdirectories of "~/Pictures/Photos Library.photoslibrary/originals". It contains subdirectories named 1, 2, ... which contain jpeg and heic files. According to MacWorld: What is HEIC?
Apple has replaced the JPEG image format with the new HEIC alternative in iOS. ... HEIC is the file format name Apple has chosen for the new HEIF standard. HEIF stands for High Efficiency Image Format, and, as the name suggests, is a more streamlined way of storing image files.
Unfortunately, the standard Go image libraries cannot handle this format.
Furtunately, there is a C library for HEIF images called libheif.
libheif is an ISO/IEC 23008-12:2017 HEIF and AVIF (AV1 Image File Format) file format decoder and encoder. There is partial support for ISO/IEC 23008-12:2022 (2nd Edition) capabilities.
It also has a go API, but requires that the C library is installed, see libheif installation:
brew install cmake make pkg-config x265 libde265 libjpeg libtool
brew install libheif
I'm not sure whether the first line actually is required.
Then continue to install the go packages as usual:
go get "github.com/strukturag/libheif/go/heif"
I was wandering why image.Decode worked only after I had installed libheif/heif. It is because the initialization registers the format heif with image (see source code) in the package init() function.
func init() {
image.RegisterFormat("heif", "????ftypheic", decodeImage, decodeConfig)
image.RegisterFormat("heif", "????ftypheim", decodeImage, decodeConfig)
image.RegisterFormat("heif", "????ftypheis", decodeImage, decodeConfig)
image.RegisterFormat("heif", "????ftypheix", decodeImage, decodeConfig)
image.RegisterFormat("heif", "????ftyphevc", decodeImage, decodeConfig)
image.RegisterFormat("heif", "????ftyphevm", decodeImage, decodeConfig)
image.RegisterFormat("heif", "????ftyphevs", decodeImage, decodeConfig)
image.RegisterFormat("heif", "????ftypmif1", decodeImage, decodeConfig)
image.RegisterFormat("avif", "????ftypavif", decodeImage, decodeConfig)
image.RegisterFormat("avif", "????ftypavis", decodeImage, decodeConfig)
}To read the heif file, use:
import (
"bytes"
"image"
"image/jpeg"
"os"
"github.com/strukturag/libheif/go/heif"
)
ver := heif.GetVersion()
println(ver)
f, err := os.Open("sample.heic")
defer f.Close()
img, fmt, err := image.Decode(f)
println(fmt)To convert it to jpeg:
outf, _ := os.Create("sample.jpeg")
defer outf.Close()
var out bytes.Buffer
if err := jpeg.Encode(&out, img, &jpeg.Options{Quality: 80}); err != nil {
panic(err)
}
_, out := outf.Write(out.Bytes())
outf.Close()Another question is to get as much information about the image as possible. This information is stored in the image file in the Exchangeable image file format Exif. According to Wikipedia Exif:
Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications)[5] is a standard that specifies formats for images, sound, and ancillary tags used by digital cameras (including smartphones), scanners and other systems handling image and sound files recorded by digital cameras.
I found the Go library imagemeta to read this data.
import (
"github.com/evanoberholster/imagemeta"
)
exif, err := imagemeta.Decode(f)
println(exif.String())
/*
Exif
ImageType: image/heif
Make: Apple
Model: iPhone 13
LensMake: Apple
LensModel: iPhone 13 back dual wide camera 5.1mm f/1.6
CameraSerial:
LensSerial:
Image Size: 4032x3024
Orientation: Horizontal
ShutterSpeed: 1/577
Aperture: 1.60
ISO: 50
Flash: Off, Did not fire
Focal Length: 5.10mm
Fl 35mm Eqv: 26.00mm
Exposure Prgm: Program AE
Metering Mode: Multi-segment
Exposure Mode: Auto
Date Modified: 2023-10-18 15:39:18 -0500 -05:00
Date Created: 2023-10-18 15:39:18.681 -0500 -05:00
Date Original: 2023-10-18 15:39:18.681 -0500 -05:00
Date GPS: 2023-10-18 00:00:00 +0000 UTC
Artist:
Copyright:
Software: 16.6.1
Image Desc:
GPS Altitude: 185.04
GPS Latitude: 41.947917
GPS Longitude: -87.656342
*/- libheif: C library with Go API for heif images libheif
go-libheif: Go Wrapper for libheif at go-libheif - imagemeta: Go package to handle image EXIF metadata at imagemeta