Swift5: obtain brightness/light level from the camera

Question

I have this code, which is an extension of AVCaptureMetadataOutputObjectsDelegate:

internal func metadataOutput(_ output: AVCaptureMetadataOutput, didOutput metadataObjects: [AVMetadataObject], from connection: AVCaptureConnection) {
        guard let captureSession = captureSession else { return }
        captureSession.stopRunning()
        if let metadataObject = metadataObjects.first {
            guard let readableObject = metadataObject as? AVMetadataMachineReadableCodeObject else { return }
            guard let stringValue = readableObject.stringValue else { return }
            AudioServicesPlaySystemSound(SystemSoundID(kSystemSoundID_Vibrate))
            found(code: stringValue)
        }
    }

And is called when it 'views' a qr code:

let metadataOutput = AVCaptureMetadataOutput()
        
        if (captureSession.canAddOutput(metadataOutput)) {
            captureSession.addOutput(metadataOutput)
            metadataOutput.setMetadataObjectsDelegate(self, queue: DispatchQueue.main)
            metadataOutput.metadataObjectTypes = [.qr]

What I want to do is to add a new functionality, which is, as soon as I open the camera, to know what is the luminosity of the back camera.

I found everywhere that they use this:

func captureOutput(_ output: AVCaptureOutput, 
                  didOutput sampleBuffer: CMSampleBuffer, 
                       from connection: AVCaptureConnection)

But it seems to me that it is not in AvFoundation anymore.

Answer 1

I assume the "luminosity" of camera you mention is some kind of a light level metric. I know several ways to measure it.

I imagine, there must already be defined a videoDevice somewhere in your code: let videoDevice: AVCaptureDevice. If you don't store it separately, get it from videoInput.videoDevice.

• Check videoDevice.iso. The lower is value - the brighter lighting conditions are. It's a KVO property, so you can observe it's change in realtime.

• Check videoDevice.exposureDuration. Same: lower value → brighter lighting conditions. Exposure duration is basically what the iOS system camera adjusts for better night mode shots.

• As you mentioned, you could also get a realtime pixel buffer from your camera to analyze. Like to build a histogram and compare light pixels to dark etc.

In your camera class:

/// You already have the session
private let session = AVCaptureSession()

/// Define a video output (probably you did that already, 
/// otherwise how would your camera scan QRs at all)
private let videoOutput = AVCaptureVideoDataOutput()

/// Define a queue for sample buffer
private let videoSampleBufferQueue = DispatchQueue(label: "videoSampleBufferQueue")

Then add output to session:

if session.canAddOutput(videoOutput){
    session.addOutput(videoOutput)
}
videoOutput.setSampleBufferDelegate(self, queue: videoSampleBufferQueue)

And implement AVCaptureVideoDataOutputSampleBufferDelegate:

func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
    guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return }
    // Handle the pixelBuffer the way you like
}