Reading QRCodes with AVCaptureSession - ios

Question

We have implemented reading QRCodes on a receipt using AVCaptureSession. One issue that we have noticed is that it is rather finicky in our hit rate of it reading the QRCode. You really have to work at it to get it to recognize that there is a QRCode on the receipt. I have paddled/googled around trying to see if anyone has published material on how to increase the hit rate. I have implemented AutoFocus and that has helped marginally.
I did take a look at: Reading on QRCodes on iOS with AVCaptureSession -- alignment issues? but there was no actionable suggestions there.
Any thoughts on other approaches?
Here is the reader code:
import UIKit
import AVFoundation
final class BarcodeReader: NSObject {
fileprivate var captureSession: AVCaptureSession?
fileprivate var videoPreviewLayer: AVCaptureVideoPreviewLayer?
fileprivate unowned let barcodeReaderDelegate: BarcodeReaderDelegate
init(barcodeReaderDelegate: BarcodeReaderDelegate) {
self.barcodeReaderDelegate = barcodeReaderDelegate
}
func start(in view: UIView) throws {
if captureSession == nil {
captureSession = try configuredCaptureSession()
}
if videoPreviewLayer == nil {
videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession!)
videoPreviewLayer!.videoGravity = AVLayerVideoGravityResizeAspectFill
videoPreviewLayer!.frame = view.layer.bounds
view.layer.addSublayer(videoPreviewLayer!)
}
captureSession!.startRunning()
}
fileprivate func configuredCaptureSession() throws -> AVCaptureSession {
let captureSession = AVCaptureSession()
// NOTE: Remember to add a message in your Info.plist file under the
// key NSCameraUsageDescription or this will crash the app.
let device = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
// make sure that auto focus is turned on
if (device?.isFocusModeSupported(.continuousAutoFocus))! {
try device?.lockForConfiguration()
device?.focusMode = .continuousAutoFocus
device?.unlockForConfiguration()
}
let input = try AVCaptureDeviceInput(device: device)
captureSession.addInput(input)
let output = AVCaptureMetadataOutput()
captureSession.addOutput(output)
output.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
output.metadataObjectTypes = [AVMetadataObjectTypeQRCode]
return captureSession
}
func stop() {
captureSession?.stopRunning()
}
}
extension BarcodeReader: AVCaptureMetadataOutputObjectsDelegate {
func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputMetadataObjects metadataObjects: [Any]!, from connection: AVCaptureConnection!) {
guard let metadataObject = metadataObjects.first as? AVMetadataMachineReadableCodeObject else { return }
guard metadataObject.type == AVMetadataObjectTypeQRCode else { return
}
stop()
barcodeReaderDelegate.barcodeReader(self, found: metadataObject.stringValue)
}
}
protocol BarcodeReaderDelegate: class {
func barcodeReader(_ barcodeReader: BarcodeReader, found code: String)
}