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How to use OpenCV in Swift (1)

November 06, 2016

I try to use OpenCV library in Swift today.

Let’s convert an picture by camera to a black-and-white image.

Environment

  • iOS9.3.4
  • Xcode8.1 (Swift3.0.1)
  • OpenCV (3.1.0.1)

Step 1

First, create a project in Xcode, and do pod init at the project top directory.

After that, edit Podfile like this.

platform :ios, '9.0'

target 'OpenCVTest' do
  use_frameworks!
  pod 'OpenCV'
end

And, install OpenCV library by pod install and open the project.

Step 2

Put an image view and a button on the first view.

The image view is for showing an image of camera, and the button is for taking a shot.

After putting, storyboard is like this.

Storyboard

Step 3

Next, get the backside camera device, and show its image in the image view you prepared.

// ViewController.swift
import UIKit
import AVFoundation

class ViewController: UIViewController, AVCaptureVideoDataOutputSampleBufferDelegate {

    @IBOutlet weak var imageView: UIImageView!

    var session : AVCaptureSession!
    var device : AVCaptureDevice!
    var output : AVCaptureVideoDataOutput!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        if initCamera() {
            session.startRunning()
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func take(_ sender: Any) {
        // when button is tapped, this method is called
    }

    func initCamera() -> Bool {
        session = AVCaptureSession()
        session.sessionPreset = AVCaptureSessionPresetMedium

        let devices = AVCaptureDevice.devices()

        for d in devices! {
            if((d as AnyObject).position == AVCaptureDevicePosition.back){
                device = d as! AVCaptureDevice
            }
        }
        if device == nil {
            return false
        }

        do {
            let myInput: AVCaptureDeviceInput?
            try myInput = AVCaptureDeviceInput(device: device)

            if session.canAddInput(myInput) {
                session.addInput(myInput)
            } else {
                return false
            }

            output = AVCaptureVideoDataOutput()
            output.videoSettings = [ kCVPixelBufferPixelFormatTypeKey as AnyHashable: Int(kCVPixelFormatType_32BGRA) ]

            try device.lockForConfiguration()
            device.activeVideoMinFrameDuration = CMTimeMake(1, 15)
            device.unlockForConfiguration()

            let queue: DispatchQueue = DispatchQueue(label: "myqueue", attributes: [])
            output.setSampleBufferDelegate(self, queue: queue)

            output.alwaysDiscardsLateVideoFrames = true
        } catch let error as NSError {
            print(error)
            return false
        }

        if session.canAddOutput(output) {
            session.addOutput(output)
        } else {
            return false
        }

        for connection in output.connections {
            if let conn = connection as? AVCaptureConnection {
                if conn.isVideoOrientationSupported {
                    conn.videoOrientation = AVCaptureVideoOrientation.portrait
                }
            }
        }

        return true
    }

    func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!,
                       from connection: AVCaptureConnection!) {
        DispatchQueue.main.async(execute: {
            let image: UIImage = CameraUtil.imageFromSampleBuffer(buffer: sampleBuffer)
            self.imageView.image = image;
        })
    }
}

The last method, captureOutput is called in every frames, and the argument, sampleBuffer has the data of camera.

Let’s convert the data to image by creating the follwing util class, and show it in imageView.

// CameraUtil.swift
import Foundation
import UIKit
import AVFoundation

class CameraUtil {
    class func imageFromSampleBuffer(buffer: CMSampleBuffer) -> UIImage {
        let pixelBuffer: CVImageBuffer = CMSampleBufferGetImageBuffer(buffer)!

        let ciImage = CIImage(cvPixelBuffer: pixelBuffer)

        let pixelBufferWidth = CGFloat(CVPixelBufferGetWidth(pixelBuffer))
        let pixelBufferHeight = CGFloat(CVPixelBufferGetHeight(pixelBuffer))
        let imageRect: CGRect = CGRectMake(0, 0, pixelBufferWidth, pixelBufferHeight)
        let ciContext = CIContext.init()
        let cgimage = ciContext.createCGImage(ciImage, from: imageRect )

        let image = UIImage(cgImage: cgimage!)
        return image
    }

    class func CGRectMake(_ x: CGFloat, _ y: CGFloat, _ width: CGFloat, _ height: CGFloat) -> CGRect {
        return CGRect(x: x, y: y, width: width, height: height)
    }
}

Step 4

Let’s check temporarily.

If the camera image is shown in the image view, then it means it works fine.

I’ll write the left steps in the next post.