Vision Framework Barcode detection for iOS 11

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 af

Answer 1

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 2

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
            })

Answer 3

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)")
}