iOS 相机面部跟踪（Swift 3 Xcode 8）

Question

我正在尝试制作一个简单的摄像头应用程序，前置摄像头可以检测人脸。 这应该很简单：

• 创建一个继承自 UIImage 的 CameraView 类并将其放置在 UI 中。确保它实现了 AVCaptureVideoDataOutputSampleBufferDelegate 以便实时处理来自相机的帧。

  class CameraView: UIImageView, AVCaptureVideoDataOutputSampleBufferDelegate 
  

• 在实例化 CameraView 时调用的函数 handleCamera 中，设置 AVCapture 会话。添加来自相机的输入。

  override init(frame: CGRect) {
      super.init(frame:frame)
  
      handleCamera()
  }
  
  func handleCamera () {
      camera = AVCaptureDevice.defaultDevice(withDeviceType: .builtInWideAngleCamera,
                                             mediaType: AVMediaTypeVideo, position: .front)
      session = AVCaptureSession()
  
      // Set recovered camera as an input device for the capture session
      do {
          try input = AVCaptureDeviceInput(device: camera);
      } catch _ as NSError {
          print ("ERROR: Front camera can't be used as input")
          input = nil
      }
  
      // Add the input from the camera to the capture session
      if (session?.canAddInput(input) == true) {
          session?.addInput(input)
      }
  

• 创建输出。创建一个串行输出队列以传递数据，然后由 AVCaptureVideoDataOutputSampleBufferDelegate（在本例中为类本身）处理该数据。将输出添加到会话。

      output = AVCaptureVideoDataOutput()
  
      output?.alwaysDiscardsLateVideoFrames = true    
      outputQueue = DispatchQueue(label: "outputQueue")
      output?.setSampleBufferDelegate(self, queue: outputQueue)
  
      // add front camera output to the session for use and modification
      if(session?.canAddOutput(output) == true){
          session?.addOutput(output)
      } // front camera can't be used as output, not working: handle error
      else {
          print("ERROR: Output not viable")
      }
  

• 设置相机预览视图并运行会话

      // Setup camera preview with the session input
      previewLayer = AVCaptureVideoPreviewLayer(session: session)
      previewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
      previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.portrait
      previewLayer?.frame = self.bounds
      self.layer.addSublayer(previewLayer!)
  
      // Process the camera and run it onto the preview
      session?.startRunning()
  

• 在委托运行的 captureOutput 函数中，将接收到的样本缓冲区转换为 CIImage 以检测人脸。如果找到人脸，请提供反馈。

  func captureOutput(_ captureOutput: AVCaptureOutput!, didDrop sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
  
  let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)
  let cameraImage = CIImage(cvPixelBuffer: pixelBuffer!)
  
  
  let accuracy = [CIDetectorAccuracy: CIDetectorAccuracyHigh]
  let faceDetector = CIDetector(ofType: CIDetectorTypeFace, context: nil, options: accuracy)
  let faces = faceDetector?.features(in: cameraImage)
  
  for face in faces as! [CIFaceFeature] {
  
        print("Found bounds are \(face.bounds)")
  
        let faceBox = UIView(frame: face.bounds)
  
        faceBox.layer.borderWidth = 3
        faceBox.layer.borderColor = UIColor.red.cgColor
        faceBox.backgroundColor = UIColor.clear
        self.addSubview(faceBox)
  
        if face.hasLeftEyePosition {
            print("Left eye bounds are \(face.leftEyePosition)")
        }
  
        if face.hasRightEyePosition {
            print("Right eye bounds are \(face.rightEyePosition)")
        }
    }
  }
  

我的问题：我可以让相机运行，但是我从互联网上尝试了许多不同的代码，我从来没有能够让 captureOutput 来检测人脸。要么应用程序没有进入函数，要么由于变量不起作用而崩溃，最常见的情况是 sampleBuffer 变量为 nul。 我做错了什么？

Answer 1

您需要将 captureOutput 函数参数更改为以下内容：func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!)

您的captureOutput 函数在缓冲区丢失时调用，而不是在从相机获取时调用。