Face detection swift vision kit - face-detection

Question

I am trying Vision kit for iOS 11. I can use Vision and I can find boundbox values face. But I don't know how can I draw a rectangle using this points. I hope so my question is clear.

Answer 1

Hope you were able to use VNDetectFaceRectanglesRequest and able to detect faces. To show rectangle boxes there are lots of ways to achieve it. But simplest one would be using CAShapeLayer to draw layer on top your image for each face you detected.
Consider you have VNDetectFaceRectanglesRequest like below
let request = VNDetectFaceRectanglesRequest { [unowned self] request, error in
if let error = error {
// somthing is not working as expected
}
else {
// we got some face detected
self.handleFaces(with: request)
}
}
let handler = VNImageRequestHandler(ciImage: ciImage, options: [:])
do {
try handler.perform([request])
}
catch {
// catch exception if any
}
You can implement a simple method called handleFace for each face detected and use VNFaceObservation property to draw a CAShapeLayer.
func handleFaces(with request: VNRequest) {
imageView.layer.sublayers?.forEach { layer in
layer.removeFromSuperlayer()
}
guard let observations = request.results as? [VNFaceObservation] else {
return
}
observations.forEach { observation in
let boundingBox = observation.boundingBox
let size = CGSize(width: boundingBox.width * imageView.bounds.width,
height: boundingBox.height * imageView.bounds.height)
let origin = CGPoint(x: boundingBox.minX * imageView.bounds.width,
y: (1 - observation.boundingBox.minY) * imageView.bounds.height - size.height)
let layer = CAShapeLayer()
layer.frame = CGRect(origin: origin, size: size)
layer.borderColor = UIColor.red.cgColor
layer.borderWidth = 2
imageView.layer.addSublayer(layer)
}
}
More info can be found here in Github repo iOS-11-by-Examples

Answer 2

Here is easy and simple way to draw boxes.
let faceRequest = VNDetectFaceRectanglesRequest(completionHandler:self.faceDetection)
func faceDetection (request: VNRequest, error: Error?) {
guard let observations = request.results as? [VNFaceObservation]
else { print("unexpected result type from VNFaceObservation")
return }
guard observations.first != nil else {
return
}
// Show the pre-processed image
DispatchQueue.main.async {
self.resultImageView.subviews.forEach({ (subview) in
subview.removeFromSuperview()
})
for face in observations
{
let view = self.CreateBoxView(withColor: UIColor.red)
view.frame = self.transformRect(fromRect: face.boundingBox, toViewRect: self.analyzedImageView)
self.analyzedImageView.image = self.originalImageView.image
self.resultImageView.addSubview(view)
}
}
}
//MARK - Instance Methods
func boxView(withColor : UIColor) -> UIView {
let view = UIView()
view.layer.borderColor = withColor.cgColor
view.layer.borderWidth = 2.0
view.backgroundColor = UIColor.clear
return view
}
//Convert Vision Frame to UIKit Frame
func transformRect(fromRect: CGRect , toViewRect :UIView) -> CGRect {
var toRect = CGRect()
toRect.size.width = fromRect.size.width * toViewRect.frame.size.width
toRect.size.height = fromRect.size.height * toViewRect.frame.size.height
toRect.origin.y = (toViewRect.frame.height) - (toViewRect.frame.height * fromRect.origin.y )
toRect.origin.y = toRect.origin.y - toRect.size.height
toRect.origin.x = fromRect.origin.x * toViewRect.frame.size.width
return toRect
}