Scale and Orient Image

scaleAndOrient.swift

  func scaleAndOrient(image: UIImage) -> UIImage {

      // Set a default value for limiting image size.
      let maxResolution: CGFloat = 640

      guard let cgImage = image.cgImage else {
          print("UIImage has no CGImage backing it!")
          return image
      }

      // Compute parameters for transform.
      let width = CGFloat(cgImage.width)
      let height = CGFloat(cgImage.height)
      var transform = CGAffineTransform.identity

      var bounds = CGRect(x: 0, y: 0, width: width, height: height)

      if width > maxResolution ||
          height > maxResolution {
          let ratio = width / height
          if width > height {
              bounds.size.width = maxResolution
              bounds.size.height = round(maxResolution / ratio)
          } else {
              bounds.size.width = round(maxResolution * ratio)
              bounds.size.height = maxResolution
          }
      }

      let scaleRatio = bounds.size.width / width
      let orientation = image.imageOrientation
      switch orientation {
      case .up:
          transform = .identity
      case .down:
          transform = CGAffineTransform(translationX: width, y: height).rotated(by: .pi)
      case .left:
          let boundsHeight = bounds.size.height
          bounds.size.height = bounds.size.width
          bounds.size.width = boundsHeight
          transform = CGAffineTransform(translationX: 0, y: width).rotated(by: 3.0 * .pi / 2.0)
      case .right:
          let boundsHeight = bounds.size.height
          bounds.size.height = bounds.size.width
          bounds.size.width = boundsHeight
          transform = CGAffineTransform(translationX: height, y: 0).rotated(by: .pi / 2.0)
      case .upMirrored:
          transform = CGAffineTransform(translationX: width, y: 0).scaledBy(x: -1, y: 1)
      case .downMirrored:
          transform = CGAffineTransform(translationX: 0, y: height).scaledBy(x: 1, y: -1)
      case .leftMirrored:
          let boundsHeight = bounds.size.height
          bounds.size.height = bounds.size.width
          bounds.size.width = boundsHeight
          transform = CGAffineTransform(translationX: height, y: width).scaledBy(x: -1, y: 1).rotated(by: 3.0 * .pi / 2.0)
      case .rightMirrored:
          let boundsHeight = bounds.size.height
          bounds.size.height = bounds.size.width
          bounds.size.width = boundsHeight
          transform = CGAffineTransform(scaleX: -1, y: 1).rotated(by: .pi / 2.0)
      }

      return UIGraphicsImageRenderer(size: bounds.size).image { rendererContext in
          let context = rendererContext.cgContext

          if orientation == .right || orientation == .left {
              context.scaleBy(x: -scaleRatio, y: scaleRatio)
              context.translateBy(x: -height, y: 0)
          } else {
              context.scaleBy(x: scaleRatio, y: -scaleRatio)
              context.translateBy(x: 0, y: -height)
          }
          context.concatenate(transform)
          context.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: height))
      }
  }

the code is from https://developer.apple.com/documentation/vision/detecting_objects_in_still_images