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使用Swift编写一个MRZ扫描应用
2024年7月10日

Dynamsoft Label Recognizer是一个用于识别区域文本的SDK。其主要用例是读取护照、身份证件上的MRZ（机器可读区域）。

在本文中，我们将使用Dynamsoft Label Recognizer和Swift编写一个iOS MRZ扫描应用。

最终结果的演示视频：

新建项目

打开Xcode并创建一个新的基于UIKit和Swift的应用项目。

由于我们将以代码方式操作UI，因此可以删除Main.storyboard和SceneDelegate.swift并更新项目和Info.plist。

添加依赖项

在这里，我们使用CocoaPods来管理依赖项。

  1. 在项目文件夹中初始化pod。

    pod init

  2. 将以下行添加到Podfile。

    pod "DynamsoftCore", "= 2.0.2"
pod "DynamsoftLabelRecognizer", '= 2.2.20'

  3. 运行pod install

添加权限

将以下内容添加到Info.plist，以获得访问摄像头的权限。

<key>NSCameraUsageDescription</key>
<string>For camera usage</string>

初始化Dynamsoft Label Recognizer的许可证

在AppDelegate.swift中，添加以下内容以初始化Dynamsoft Label Recognizer的许可证。可以在此处申请一个30天试用许可证。

@main
class AppDelegate: UIResponder, UIApplicationDelegate, LicenseVerificationListener  {
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        let trialLicense = "DLS2eyJoYW5kc2hha2VDb2RlIjoiMjAwMDAxLTE2NDk4Mjk3OTI2MzUiLCJvcmdhbml6YXRpb25JRCI6IjIwMDAwMSIsInNlc3Npb25QYXNzd29yZCI6IndTcGR6Vm05WDJrcEQ5YUoifQ=="; //one-day public trial
        DynamsoftLicenseManager.initLicense(trialLicense,verificationDelegate:self)
        return true
    }

    func licenseVerificationCallback(_ isSuccess: Bool, error: Error?) {
        var msg:String? = ""
        if isSuccess {
            print("license valid")
        }
        if(error != nil)
        {
            let err = error as NSError?
            if err?.code == -1009 {
                msg = "Dynamsoft Label Recognizer is unable to connect to the public Internet to acquire a license. Please connect your device to the Internet or contact support@dynamsoft.com to acquire an offline license."
            }else{
                msg = err!.userInfo[NSUnderlyingErrorKey] as? String
                if(msg == nil)
                {
                    msg = err?.localizedDescription
                }
            }
            print(msg ?? "")
        }
    }
}

接下来，我们将分步实现页面。有两个页面：主页和摄像头页面。

主页

添加Scan MRZ按钮以导航到摄像头页面。

class ViewController: UIViewController {
    var button: UIButton!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.

        self.button = UIButton(frame: .zero)
        self.button.setTitle("Scan MRZ", for: .normal)
        self.button.setTitleColor(.systemBlue, for: .normal)
        self.button.setTitleColor(.lightGray, for: .highlighted)

        self.button.addTarget(self,
                         action: #selector(buttonAction),
                         for: .touchUpInside)
        self.navigationItem.title = "Home"

        self.view.backgroundColor = UIColor.white
        self.view.addSubview(self.button)
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        if let button = self.button {
            let width: CGFloat = 300
            let height: CGFloat = 50
            let x = view.frame.width/2 - width/2
            let y = view.frame.height - 100
            button.frame = CGRect.init(x: x, y: y, width: width, height: height)
        }
    }

    @objc
    func buttonAction() {
        self.navigationController?.pushViewController(CameraController(), animated: true)
    }
}

由于我们没有使用storyboard，因此需要在AppDelegate.swift中使用以下代码显示主页。

@main
class AppDelegate: UIResponder, UIApplicationDelegate, LicenseVerificationListener  {
    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        window = UIWindow(frame: UIScreen.main.bounds)
        let vc = ViewController()
        let navController = UINavigationController(rootViewController: vc)
        window?.rootViewController = navController
        window?.makeKeyAndVisible()
        //...
        return true
    }
}

摄像头页面

创建一个名为CameraController.swift的新的视图控制器。然后，我们将在此页面启动摄像头并扫描MRZ。

使用AVFoundation启动摄像头

  1. 创建名为PreviewView的视图来显示摄像头预览。

    import UIKit

//https://developer.apple.com/documentation/avfoundation/capture_setup/setting_up_a_capture_session?language=objc#2958852
class PreviewView: UIView {
    override class var layerClass: AnyClass {
        return AVCaptureVideoPreviewLayer.self
    }
    /// Convenience wrapper to get layer as its statically known type.
    var videoPreviewLayer: AVCaptureVideoPreviewLayer {
        return layer as! AVCaptureVideoPreviewLayer
    }
}

  2. 将PreviewView添加到摄像头控制器。

    var previewView: PreviewView!
override func viewDidLoad() {
    super.viewDidLoad()
    self.previewView = PreviewView()
    self.view.addSubview(self.previewView)
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    if let previewView = self.previewView {
        let width: CGFloat = view.frame.width
        let height: CGFloat = view.frame.height
        let x: CGFloat = 0.0
        let y: CGFloat = 0.0
        previewView.frame = CGRect.init(x: x, y: y, width: width, height: height)
    }
}

  3. 打开摄像头并开始捕获会话。

    var captureSession: AVCaptureSession!
func startCamera(){
    // Create the capture session.
    self.captureSession = AVCaptureSession()

    // Find the default video device.
    guard let videoDevice = AVCaptureDevice.default(for: .video) else { return }

    do {
        // Wrap the video device in a capture device input.
        let videoInput = try AVCaptureDeviceInput(device: videoDevice)
        // If the input can be added, add it to the session.
        if self.captureSession.canAddInput(videoInput) {
            self.captureSession.addInput(videoInput)
            self.previewView.videoPreviewLayer.session = self.captureSession

            //set the camera preview's resolution
            self.captureSession.sessionPreset = AVCaptureSession.Preset.hd1920x1080

            self.captureSession.startRunning()
        }
    } catch {
        // Configuration failed. Handle error.
    }
}

从相机预览扫描MRZ

  1. 导入库。

    import DynamsoftCore
import DynamsoftLabelRecognizer

  2. 创建Label Recognizer实例。

    var recognizer:DynamsoftLabelRecognizer = DynamsoftLabelRecognizer();

  3. 加载MRZ模型。

    1. 将MRZ模型文件夹以reference的形式添加。可以在此处找到这些文件。

      将模型添加到项目

    2. 使用代码加载模型文件。

      func loadModel(){
    let modelFolder = "MRZ"
    let modelFileNames = ["MRZ"]

    for model in modelFileNames {

        guard let prototxt = Bundle.main.url(
            forResource: model,
            withExtension: "prototxt",
            subdirectory: modelFolder
        ) else {
            print("model not exist")
            return
        }

        let datapro = try! Data.init(contentsOf: prototxt)
        let txt = Bundle.main.url(forResource: model, withExtension: "txt", subdirectory: modelFolder)
        let datatxt = try! Data.init(contentsOf: txt!)
        let caffemodel = Bundle.main.url(forResource: model, withExtension: "caffemodel", subdirectory: modelFolder)
        let datacaf = try! Data.init(contentsOf: caffemodel!)
        DynamsoftLabelRecognizer.appendCharacterModel(model, prototxtBuffer: datapro, txtBuffer: datatxt, characterModelBuffer: datacaf)
        print("load model %@", model)
    }
}

  4. 更新Label Recognizer的设置以识别MRZ。

    let template = "{\"CharacterModelArray\":[{\"DirectoryPath\":\"\",\"Name\":\"MRZ\"}],\"LabelRecognizerParameterArray\":[{\"Name\":\"default\",\"ReferenceRegionNameArray\":[\"defaultReferenceRegion\"],\"CharacterModelName\":\"MRZ\",\"LetterHeightRange\":[5,1000,1],\"LineStringLengthRange\":[30,44],\"LineStringRegExPattern\":\"([ACI][A-Z<][A-Z<]{3}[A-Z0-9<]{9}[0-9][A-Z0-9<]{15}){(30)}|([0-9]{2}[(01-12)][(01-31)][0-9][MF<][0-9]{2}[(01-12)][(01-31)][0-9][A-Z<]{3}[A-Z0-9<]{11}[0-9]){(30)}|([A-Z<]{0,26}[A-Z]{1,3}[(<<)][A-Z]{1,3}[A-Z<]{0,26}<{0,26}){(30)}|([ACIV][A-Z<][A-Z<]{3}([A-Z<]{0,27}[A-Z]{1,3}[(<<)][A-Z]{1,3}[A-Z<]{0,27}){(31)}){(36)}|([A-Z0-9<]{9}[0-9][A-Z<]{3}[0-9]{2}[(01-12)][(01-31)][0-9][MF<][0-9]{2}[(01-12)][(01-31)][0-9][A-Z0-9<]{8}){(36)}|([PV][A-Z<][A-Z<]{3}([A-Z<]{0,35}[A-Z]{1,3}[(<<)][A-Z]{1,3}[A-Z<]{0,35}<{0,35}){(39)}){(44)}|([A-Z0-9<]{9}[0-9][A-Z<]{3}[0-9]{2}[(01-12)][(01-31)][0-9][MF<][0-9]{2}[(01-12)][(01-31)][0-9][A-Z0-9<]{14}[A-Z0-9<]{2}){(44)}\",\"MaxLineCharacterSpacing\":130,\"TextureDetectionModes\":[{\"Mode\":\"TDM_GENERAL_WIDTH_CONCENTRATION\",\"Sensitivity\":8}],\"Timeout\":9999}],\"LineSpecificationArray\":[{\"BinarizationModes\":[{\"BlockSizeX\":30,\"BlockSizeY\":30,\"Mode\":\"BM_LOCAL_BLOCK\",\"MorphOperation\":\"Close\"}],\"LineNumber\":\"\",\"Name\":\"defaultTextArea->L0\"}],\"ReferenceRegionArray\":[{\"Localization\":{\"FirstPoint\":[0,0],\"SecondPoint\":[100,0],\"ThirdPoint\":[100,100],\"FourthPoint\":[0,100],\"MeasuredByPercentage\":1,\"SourceType\":\"LST_MANUAL_SPECIFICATION\"},\"Name\":\"defaultReferenceRegion\",\"TextAreaNameArray\":[\"defaultTextArea\"]}],\"TextAreaArray\":[{\"Name\":\"defaultTextArea\",\"LineSpecificationNameArray\":[\"defaultTextArea->L0\"]}]}"
try? recognizer.initRuntimeSettings(template)

  5. 添加视频输出，以便我们可以获取相机预览的数据。

    func startCamera(){
    // Create the capture session.
    self.captureSession = AVCaptureSession()

    // Find the default video device.
    guard let videoDevice = AVCaptureDevice.default(for: .video) else { return }

    do {
        // Wrap the video device in a capture device input.
        let videoInput = try AVCaptureDeviceInput(device: videoDevice)
        // If the input can be added, add it to the session.
        if self.captureSession.canAddInput(videoInput) {
            self.captureSession.addInput(videoInput)
            self.previewView.videoPreviewLayer.session = self.captureSession

            //set the camera preview's resolution
            self.captureSession.sessionPreset = AVCaptureSession.Preset.hd1920x1080

+           self.videoOutput = AVCaptureVideoDataOutput.init()
+           if self.captureSession.canAddOutput(self.videoOutput) {
+               self.captureSession.addOutput(videoOutput)
+           }
+           
+           var queue:DispatchQueue
+           queue = DispatchQueue(label: "queue")
+           self.videoOutput.setSampleBufferDelegate(self as AVCaptureVideoDataOutputSampleBufferDelegate, queue: queue)
+           self.videoOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey : kCVPixelFormatType_32BGRA] as [String : Any]

            self.captureSession.startRunning()
        }
    } catch {
        // Configuration failed. Handle error.
    }
}

+ func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection){
+    print("capture output")
+ }

  6. 将CMSampleBuffer转换为iImageData，然后使用Dynamsoft Label Recognizer扫描MRZ。

    //convert CMSampleBuffer to iImageData
let imageBuffer:CVImageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
CVPixelBufferLockBaseAddress(imageBuffer, .readOnly)
let baseAddress = CVPixelBufferGetBaseAddress(imageBuffer)
let bufferSize = CVPixelBufferGetDataSize(imageBuffer)
let width = CVPixelBufferGetWidth(imageBuffer)
let height = CVPixelBufferGetHeight(imageBuffer)
let bpr = CVPixelBufferGetBytesPerRow(imageBuffer)
CVPixelBufferUnlockBaseAddress(imageBuffer, .readOnly)
let buffer = Data(bytes: baseAddress!, count: bufferSize)

let imageData = iImageData.init()
imageData.bytes = buffer
imageData.width = width
imageData.height = height
imageData.stride = bpr
imageData.format = .ARGB_8888

//recognize text from the image data
let results = try? recognizer.recognizeBuffer(imageData)

处理方向

摄像头传感器的自然方向是当手机处于横向右（主页按钮在右侧）时的方向。如果我们以纵向握持手机，视频帧的方向不会改变，但预览可以被旋转以配合显示。我们需要处理方向，以便Label Recognizer能够识别文本。

  1. 添加一个监听器来监听方向的变化。

    override func viewDidLoad() {
    NotificationCenter.default.addObserver(self, selector: #selector(rotated), name: UIDevice.orientationDidChangeNotification, object: nil)
}

  2. 更新预览视图的边界，并根据设备的方向更新视频方向。

    @objc func rotated() {
    let bounds = view.bounds
    self.previewView.frame = bounds
    if UIDevice.current.orientation == UIDeviceOrientation.portrait {
        self.previewView.videoPreviewLayer.connection?.videoOrientation = .portrait
    }else if UIDevice.current.orientation == UIDeviceOrientation.landscapeLeft {
        self.previewView.videoPreviewLayer.connection?.videoOrientation = .landscapeRight
    }else if UIDevice.current.orientation == UIDeviceOrientation.landscapeRight {
        self.previewView.videoPreviewLayer.connection?.videoOrientation = .landscapeLeft
    }
}

  3. 设置图像数据的方向属性，以便Label Recognizer可以正确处理方向。

    if self.previewView.videoPreviewLayer.connection?.videoOrientation == .portrait {
    imageData.orientation = 90
}else if self.previewView.videoPreviewLayer.connection?.videoOrientation == .landscapeLeft {
    imageData.orientation = 180
}

验证识别结果

单帧的识别结果可能包含错误识别的字符。我们可以存储连续识别到的结果，并检查结果是否彼此匹配，以确保我们得到可靠的结果。

以下是执行此操作的代码：

var scannedResults:[String] = []
func isSteady(results:[iDLRResult]) -> Bool {
    let str = getMRZString(results: results)
    if scannedResults.count == 5 {
        var correctNumber = 0
        for scannedResult in scannedResults {
            if str == scannedResult {
                correctNumber = correctNumber + 1
            }
        }
        if correctNumber >= 2 { // among 5 results, at least 2 are the same
            return true
        }else{
            scannedResults.remove(at: 0)
            scannedResults.append(str)
        }
    }else{
        scannedResults.append(str)
    }
    return false
}

func getMRZString(results:[iDLRResult]) -> String{
    var MRZString = ""
    for lineResult in results[0].lineResults! {
        print(lineResult.text!)
        MRZString = MRZString + lineResult.text! + "\n"
    }
    return MRZString
}

解析MRZ

最后，我们可以使用第三方解析器来解析结果。

import QKMRZParser

var mrzLines:[String] = []
for lineResult in results![0].lineResults! {
    mrzLines.append(lineResult.text!)
}

let mrzParser = QKMRZParser(ocrCorrection: true)
let result = mrzParser.parse(mrzLines: mrzLines)

var parsed = ""
parsed = parsed + "No.: " + result!.documentNumber + "\n"
parsed = parsed + "Country.: " + result!.countryCode + "\n"
parsed = parsed + "Given names: " + result!.givenNames + "\n"
parsed = parsed + "Surname: " + result!.surnames + "\n"
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "d.M.yyyy"
parsed = parsed + "Date of birth: " + dateFormatter.string(from: result!.birthdate!) + "\n"
self.label.text = parsed

源代码

欢迎下载源代码并尝试使用：https://github.com/tony-xlh/iOS-MRZ-Scanner

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