ios - 将 Vision boundingBox 从 VNFaceObservation 转换为矩形以在图像上绘制

Question

我正在尝试使用新的 Vision API 中的 VNDetectFaceRectanglesRequest 来检测图像上的人脸。然后，我在每个检测到的脸上画一个红色矩形。

但我在将 boundingBox 从 VNFaceObservation 转换为 CGRect 时遇到问题。看来我唯一的问题是 y 来源。

---

这是我的代码:

let request=VNDetectFaceRectanglesRequest{request, error in
    var final_image=UIImage(ciImage: image)
    if let results=request.results as? [VNFaceObservation]{
        for face_obs in results{
          UIGraphicsBeginImageContextWithOptions(final_image.size, false, 1.0)
          final_image.draw(in: CGRect(x: 0, y: 0, width: final_image.size.width, height: final_image.size.height))

          var rect=face_obs.boundingBox
/*/*/*/ RESULT 2 is when I uncomment this line to "flip" the y  /*/*/*/
          //rect.origin.y=1-rect.origin.y
          let conv_rect=CGRect(x: rect.origin.x*final_image.size.width, y: rect.origin.y*final_image.size.height, width: rect.width*final_image.size.width, height: rect.height*final_image.size.height)

          let c=UIGraphicsGetCurrentContext()!
          c.setStrokeColor(UIColor.red.cgColor)
          c.setLineWidth(0.01*final_image.size.width)
          c.stroke(conv_rect)

          let result=UIGraphicsGetImageFromCurrentImageContext()
          UIGraphicsEndImageContext()

          final_image=result!
        }
    }
    DispatchQueue.main.async{
        self.image_view.image=final_image
    }
}


let handler=VNImageRequestHandler(ciImage: image)
DispatchQueue.global(qos: .userInteractive).async{
    do{
        try handler.perform([request])
    }catch{
        print(error)
    }
}

---

这是目前的结果。

结果 1(不翻转 y)

结果 2(翻转 y)

---

---

解决方案

我自己为 rect 找到了解决方案。

let rect=face_obs.boundingBox
let x=rect.origin.x*final_image.size.width
let w=rect.width*final_image.size.width
let h=rect.height*final_image.size.height
let y=final_image.size.height*(1-rect.origin.y)-h
let conv_rect=CGRect(x: x, y: y, width: w, height: h)

但是，我将@wei-jay 的回答标记为好回答，因为它更优雅。

Answer 1

有内置方法可以为您完成。要从规范化形式转换，请使用:

func VNImageRectForNormalizedRect(_ normalizedRect: CGRect, _ imageWidth: Int, _ imageHeight: Int) -> CGRect

反之亦然:

func VNNormalizedRectForImageRect(_ imageRect: CGRect, _ imageWidth: Int, _ imageHeight: Int) -> CGRect

积分的类似方法:

func VNNormalizedFaceBoundingBoxPointForLandmarkPoint(_ faceLandmarkPoint: vector_float2, _ faceBoundingBox: CGRect, _ imageWidth: Int, _ imageHeight: Int) -> CGPoint
func VNImagePointForNormalizedPoint(_ normalizedPoint: CGPoint, _ imageWidth: Int, _ imageHeight: Int) -> CGPoint