ExifInterface gives me wrong rotation

Question

I would like to convert a landscape format into a portrait format. For this I use the following code. The problem is that the rotation in the end is not right, see second picture. What do I have to change?

private fun checkRotation(savedUri: Uri) {

    val path =  getRealPathFromURI(savedUri,this@NewStore)

    val exif = ExifInterface(path!!)
    val rotation =
        exif.getAttributeInt(ExifInterface.TAG_ORIENTATION, ExifInterface.ORIENTATION_UNDEFINED)
    val rotationInDegrees: Int = exifToDegrees(rotation)
    val matrix = Matrix()
    if (rotation != 0) {
        matrix.postRotate(rotationInDegrees.toFloat())
    }

    val sourceBitmap = MediaStore.Images.Media.getBitmap(contentResolver, savedUri)
    
    val rotatedBitmap =
        Bitmap.createBitmap(sourceBitmap, 0, 0, sourceBitmap.width, sourceBitmap.height, matrix, true)


    val bitmap =  rotatedBitmap.compress(Bitmap.CompressFormat.JPEG, 100, FileOutputStream(path!!))

    sourceBitmap.recycle()
    rotatedBitmap.recycle()
}

//exifOrientation has the value 6 here
private fun exifToDegrees(exifOrientation: Int): Int {
    val rotationInDegrees = when (exifOrientation) {
        ExifInterface.ORIENTATION_ROTATE_90 -> 90
        ExifInterface.ORIENTATION_ROTATE_180 -> 180
        ExifInterface.ORIENTATION_ROTATE_270 -> 270
        ExifInterface.ORIENTATION_TRANSVERSE -> -90
        ExifInterface.ORIENTATION_TRANSPOSE -> -270
        else -> 0
    }

    return rotationInDegrees
 }

This is the original shot in landscape format

And that's after I did the rotation with ExifInterface

Answer 1

First, the rotation in the orientation tag is clockwise.

See: https://exiftool.org/TagNames/EXIF.html

While the rotation that android.graphics.Matrix performs is counterclockwise.

So you should rotate -90 degrees for ORIENTATION_ROTATE_90 for example.

Second, ORIENTATION_TRANSPOSE and ORIENTATION_TRANSVERSE require rotation and flipping. You can combine rotation and scale in the same matrix for this.

Third, you are not handling some of the possible orientations: ORIENTATION_FLIP_HORIZONTAL, ORIENTATION_FLIP_VERTICAL. This can be done by scaling either X or Y by -1.