How to detect barcode using Apple Vision in CGRect only? - ios

Question

I have an app that uses a CGRect(x: 0, y: 0, width: 335, height: 150) to show the camera for barcode scanning. However when presented a barcode off camera (not in the CGRect) will get scanned. How can I limit the area for scanning to the CGRect in my preview layer? This is using Vision.
let captureSession = AVCaptureSession()
var previewLayer: AVCaptureVideoPreviewLayer!
var activeInput: AVCaptureDeviceInput!
lazy var detectBarcodeRequest = VNDetectBarcodesRequest { request, error in
guard error == nil else {
print("Barcode Error: \(String(describing: error?.localizedDescription))")
return
}
self.processBarCode(request)
}
override func viewDidLoad() {
super.viewDidLoad()
setupSession()
setupPreview()
startSession()
}
func setupSession() {
guard let camera = AVCaptureDevice.default(for: .video) else {
return
}
do {
let videoInput = try AVCaptureDeviceInput(device: camera)
for input in [videoInput] {
if captureSession.canAddInput(input) {
captureSession.addInput(input)
}
}
activeInput = videoInput
} catch {
print("Error setting device input: \(error)")
return
}
let captureOutput = AVCaptureVideoDataOutput()
captureOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)]
captureOutput.setSampleBufferDelegate(self, queue: DispatchQueue.global(qos: DispatchQoS.QoSClass.default))
captureSession.addOutput(captureOutput)
}
func setupPreview() {
previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
previewLayer.videoGravity = .resizeAspectFill
previewLayer.connection?.videoOrientation = .portrait
previewLayer.frame = CGRect(x: 0, y: 0, width: 335, height: 150)
view.layer.insertSublayer(previewLayer, at: 0)
}//setupPreview
func startSession() {
if !captureSession.isRunning {
DispatchQueue.global(qos: .default).async { [weak self] in
self?.captureSession.startRunning()
}
}
}
// MARK: - processBarCode
func processBarCode(_ request: VNRequest) {
DispatchQueue.main.async {
guard let results = request.results as? [VNBarcodeObservation] else {
return
}
if let payload = results.first?.payloadStringValue, let symbology = results.first?.symbology {
print("payload is \(payload) \(symbology) ")
}
}
}//processBarCode
Edit:
// MARK: - AVCaptureVideoDataOutputSampleBufferDelegate
extension CameraViewController: AVCaptureVideoDataOutputSampleBufferDelegate {
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return }
let imageRequestHandler = VNImageRequestHandler(
cvPixelBuffer: pixelBuffer,
orientation: .up)
do {
try imageRequestHandler.perform([detectBarcodeRequest])
} catch {
print(error)
}
}//captureOutput
}//extension

Answer 1

extension AVCaptureVideoPreviewLayer {
func rectOfInterestConverted(parentRect: CGRect, fromLayerRect: CGRect) -> CGRect {
let parentWidth = parentRect.width
let parentHeight = parentRect.height
let newX = (parentWidth - fromLayerRect.maxX)/parentWidth
let newY = 1 - (parentHeight - fromLayerRect.minY)/parentHeight
let width = 1 - (fromLayerRect.minX/parentWidth + newX)
let height = (fromLayerRect.maxY/parentHeight) - newY
return CGRect(x: newX, y: newY, width: width, height: height)
}
}
Usage:
if let rect = videoPreviewLayer?.rectOfInterestConverted(parentRect: self.view.frame, fromLayerRect: scanAreaView.frame) {
captureMetadataOutput.rectOfInterest = rect
}

Answer 2

In func captureOutput(_:didOutput:from:) you most likely passing whole image into VNImageRequestHandler.
Instead you need to crop image to your visible rect.
Another approach would be lock Vision to only visible part of image via regionOfInterest as #HurricaneOnTheMoon proposed below.

Answer 3

You can use a property regionOfInterest of VNDetectBarcodesRequest to setup a detection region.
The default value is { { 0, 0 }, { 1, 1 } } according to the Apple documentation