Vision Framework Barcode detection for iOS 11 - barcode

Question

I've been implementing a test of the new Vision framework which Apple introduced in WWDC2017. I am specifically looking at the barcode detection - I've been able to get after scanning the image from Camera/Gallery that it's a barcode image or not. However, I can't see what the actual barcode value or the payload data when looking at the barcodeDescriptor. There appears to be nothing exposed on the https://developer.apple.com/documentation/coreimage/cibarcodedescriptor page to identify any of the properties.
I am getting these errors:
Cannot connect to remote service: Error Domain=NSCocoaErrorDomain Code=4097 "connection to service named
com.apple.BarcodeSupport.BarcodeNotificationService"
libMobileGestalt MobileGestalt.c:555: no access to InverseDeviceID (see problem/11744455>)
connection to service named com.apple.BarcodeSupport.BarcodeNotificationService Error
Domain=NSCocoaErrorDomain Code=4097
Is there any way to access the barcode value from the VNBarcodeObservation?
Any help would be greatly appreciated. Thank you!
Here is the code I am using:
#IBAction func chooseImage(_ sender: Any) {
imagePicker.allowsEditing = true
imagePicker.sourceType = .photoLibrary
present(imagePicker, animated: true, completion: nil)
}
#IBAction func takePicture(_ sender: Any) {
if(UIImagePickerController .isSourceTypeAvailable(UIImagePickerControllerSourceType.camera)){
imagePicker.sourceType = UIImagePickerControllerSourceType.camera
self .present(imagePicker, animated: true, completion: nil)
}
else{
let alert = UIAlertController(title: "Warning", message: "Camera not available", preferredStyle: UIAlertControllerStyle.alert)
alert.addAction(UIAlertAction(title: "Dismiss", style: UIAlertActionStyle.default, handler: nil))
self.present(alert, animated: true, completion: nil)
}
}
//PickerView Delegate Methods
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
imagePicker .dismiss(animated: true, completion: nil)
classificationLabel.text = "Analyzing Image…"
guard let pickedImage = info[UIImagePickerControllerOriginalImage] as? UIImage
else { fatalError("no image from image picker") }
guard let ciImage = CIImage(image: pickedImage)
else { fatalError("can't create CIImage from UIImage") }
imageView.image = pickedImage
inputImage = ciImage
// Run the rectangle detector, which upon completion runs the ML classifier.
let handler = VNImageRequestHandler(ciImage: ciImage, options: [.properties : ""])
DispatchQueue.global(qos: .userInteractive).async {
do {
try handler.perform([self.barcodeRequest])
} catch {
print(error)
}
}
}
func imagePickerControllerDidCancel(_ picker: UIImagePickerController){
picker .dismiss(animated: true, completion: nil)
print("picker cancel.")
}
lazy var barcodeRequest: VNDetectBarcodesRequest = {
return VNDetectBarcodesRequest(completionHandler: self.handleBarcodes)
}()
func handleBarcodes(request: VNRequest, error: Error?) {
guard let observations = request.results as? [VNBarcodeObservation]
else { fatalError("unexpected result type from VNBarcodeRequest") }
guard observations.first != nil else {
DispatchQueue.main.async {
self.classificationLabel.text = "No Barcode detected."
}
return
}
// Loop through the found results
for result in request.results! {
// Cast the result to a barcode-observation
if let barcode = result as? VNBarcodeObservation {
// Print barcode-values
print("Symbology: \(barcode.symbology.rawValue)")
if let desc = barcode.barcodeDescriptor as? CIQRCodeDescriptor {
let content = String(data: desc.errorCorrectedPayload, encoding: .utf8)
// FIXME: This currently returns nil. I did not find any docs on how to encode the data properly so far.
print("Payload: \(String(describing: content))\n")
print("Error-Correction-Level: \(desc.errorCorrectedPayload)\n")
print("Symbol-Version: \(desc.symbolVersion)\n")
}
}
}
}

Answer 1

Apparently, in the iOS 11 beta 5 Apple introduced new payloadStringValue property of VNBarcodeObservation. Now you can read info from QR-code with no problems
if let payload = barcodeObservation.payloadStringValue {
print("payload is \(payload)")
}

Answer 2

If Apple is not going to provide a library for this, something like the following will work:
extension CIQRCodeDescriptor {
var bytes: Data? {
return errorCorrectedPayload.withUnsafeBytes { (pointer: UnsafePointer<UInt8>) in
var cursor = pointer
let representation = (cursor.pointee >> 4) & 0x0f
guard representation == 4 /* byte encoding */ else { return nil }
var count = (cursor.pointee << 4) & 0xf0
cursor = cursor.successor()
count |= (cursor.pointee >> 4) & 0x0f
var out = Data(count: Int(count))
guard count > 0 else { return out }
var prev = (cursor.pointee << 4) & 0xf0
for i in 2...errorCorrectedPayload.count {
if (i - 2) == count { break }
let cursor = pointer.advanced(by: Int(i))
let byte = cursor.pointee
let current = prev | ((byte >> 4) & 0x0f)
out[i - 2] = current
prev = (cursor.pointee << 4) & 0xf0
}
return out
}
}
}
And then
String(data: descriptor.bytes!, encoding: .utf8 /* or whatever */)

Answer 3

If you want to get the raw Data from the VNBarcodeObservation directly without it having to conform to some string encoding you can strip of the first 2 and 1/2 bytes like this, and get actual data without the QR code header.
guard let barcode = barcodeObservation.barcodeDescriptor as? CIQRCodeDescriptor else { return }
let errorCorrectedPayload = barcode.errorCorrectedPayload
let payloadData = Data(bytes: zip(errorCorrectedPayload.advanced(by: 2),
errorCorrectedPayload.advanced(by: 3)).map { (byte1, byte2) in
return byte1 << 4 | byte2 >> 4
})