Golang some images are rotating on image upload - go

Question

I am facing a rather weird problem, I am using Golang as a backend restful API and I upload images and resize them with Go . I have an app for I-phone that I am testing and if I upload an image using my real device the image gets saved in my s3 account sideways. For some reason resizing my image is rotating it, however if I upload the image from my Xcode IDE then the image gets saved correctly without rotation . I am thinking that maybe something is getting stripped however I have no idea what that could, my code is this
func UploadStreamImage(w http.ResponseWriter, r *http.Request) {
r.ParseForm()
var buff bytes.Buffer
var result string
wg := sync.WaitGroup{}
print("Exoler-Streams")
wg.Add(1)
go func() {
defer wg.Done()
sess, _ := 's3 credentials'
svc := s3.New(sess)
file, handler, err := r.FormFile("file")
if err != nil {
fmt.Println("Error Uploading Image")
return
}
defer file.Close()
// resize image
img,err := imaging.Decode(file)
if err != nil {
print("Imaging Open error")
}
new_image := imaging.Resize(img, 300, 300, imaging.Lanczos)
var buf bytes.Buffer
err = imaging.Encode(&buf,new_image, imaging.JPEG)
if err != nil {
log.Println(err)
return
}
// end resize
r := bytes.NewReader(buf.Bytes())
read_file,err := ioutil.ReadAll(r)
if err != nil {
fmt.Println("Error Reading file")
}
// s3 specific code
}
The library I am using is this https://github.com/disintegration/imaging and I am just thinking that something is being stripped when uploading the image from my real device thus it is messing up the rotation . The code on the front-end is all the same for my real device and Xcode .

Answer 1

The image is not being rotated in the process, the original image was shown in some image view software in rotated mode depending on the image orientation tag (val x00112) in the Exif part of the file. When you strip the Exif part, as image package does, you lose that information and the image is shown in standard camera orientation format (landscape).

Answer 2

Old question but i thought i would add some extra information here to help anyone who is confused about what Exif is.
When an image is uploaded from a phone it stays in the orientation that it was taken in. However meta data is then added to that image under the key Orientation to tell you which way the image was taken. Phone libaries can then use this to show you the image the correct way around and so can you. It can be a number between 0 - 8. The only orientation numbers you will need to worry about is 3 (rotate 180), 6 (rotate 270) and 8 (rotate 90).
To get a hold of the meta information on an image you can use something like github.com/rwcarlsen/goexif/exif. Here is a snippet on how you can then get the rotation from that.
x, err := exif.Decode(openedFileExif)
var rotation float64 = 0
if err == nil {
orientationRaw, err := x.Get("Orientation")
if err == nil {
orientation := orientationRaw.String()
if orientation == "3" {
rotation = 180
} else if orientation == "6" {
rotation = 270
} else if orientation == "8" {
rotation = 90
}
}
}
Now that you have the rotation required you just need to rotate the image by that amount and you will have your normally oriented picture.
You can use something like github.com/disintegration/imaging for that. uploadedImage needs to be golang image.Image
if rotation != 0 {
uploadedImage = imaging.Rotate(uploadedImage, rotation, color.Gray{})
}