vision.swift

//: A UIKit based Playground to present user interface
  
import UIKit
import Vision
import PlaygroundSupport

class ViewController : UIViewController {
    let imageView = UIImageView()
    let overlayImageView = UIImageView()

    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        imageView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        imageView.frame = view.bounds
        imageView.contentMode = .scaleAspectFit
        view.addSubview(imageView)

        overlayImageView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        overlayImageView.frame = view.bounds
        overlayImageView.contentMode = .scaleAspectFit
        view.addSubview(overlayImageView)

        self.view = view
    }
}

let viewController = ViewController()

let image = #imageLiteral(resourceName: "sample02.jpg")

viewController.imageView.image = image

guard let cgImage = image.cgImage else {
    fatalError()
}

let size = image.size

let request = VNDetectTextRectanglesRequest { request, error in
    guard error == nil else {
        fatalError()
    }

    guard let observations = request.results as? [VNDetectedObjectObservation] else {
        fatalError()
    }

    let renderer = UIGraphicsImageRenderer(size: size)
    let boxes = observations
        .map({ $0.boundingBox.applying(CGAffineTransform(scaleX: size.width, y: size.height)) })
    viewController.overlayImageView.image = renderer.image { context in
        UIColor.red.setStroke()

        for box in boxes {
            var newBox = box
            newBox.origin.y = size.height - box.maxY
            context.stroke(newBox)
        }
    }
}

let handler = VNImageRequestHandler(cgImage: cgImage, options: [:])
try! handler.perform([request])

PlaygroundPage.current.liveView = viewController