AVCaptureDevice Camera Zoom

Question

I have a simple AVCaptureSession running to get a camera feed in my app and take photos. How can I implement the 'pinch to zoom' functionality using a UIGestureRecognizer for the camera?

Answer 1

The accepted answer is actually outdated and I'm not sure it will actually take the photo of the zoomed in image. There is a method to zoom in like bcattle answer says. The problem of his answer is that it does not take in charge the fact that the user can zoom in and then restart from that zoom position. His solution will create some kind of jumps that are not really elegant.

The easiest and most elegant way of doing this is to use the velocity of the pinch gesture.

-(void) handlePinchToZoomRecognizer:(UIPinchGestureRecognizer*)pinchRecognizer {
    const CGFloat pinchVelocityDividerFactor = 5.0f;

    if (pinchRecognizer.state == UIGestureRecognizerStateChanged) {
        NSError *error = nil;
        if ([videoDevice lockForConfiguration:&error]) {
            CGFloat desiredZoomFactor = device.videoZoomFactor + atan2f(pinchRecognizer.velocity, pinchVelocityDividerFactor);
            // Check if desiredZoomFactor fits required range from 1.0 to activeFormat.videoMaxZoomFactor
            device.videoZoomFactor = MAX(1.0, MIN(desiredZoomFactor, device.activeFormat.videoMaxZoomFactor));
            [videoDevice unlockForConfiguration];
        } else {
            NSLog(@"error: %@", error);
        }
    }
}

I found that adding the arctan function to the velocity will ease the zoom in zoom out effect a bit. It is not exactly perfect but the effect is good enough for the needs. There could probably be another function to ease the zoom out when it almost reaches 1.

NOTE: Also, the scale of a pinch gesture goes from 0 to infinite with 0 to 1 being pinching in (zoom out) and 1 to infinite being pinching out (zoom in). To get a good zoom in zoom out effect with this you'd need to have a math equation. Velocity is actually from -infinite to infinite with 0 being the starting point.

EDIT: Fixed crash on range exception. Thanks to @garafajon!

Answer 2

Many have tried to do this by setting the transform property on the layer to CGAffineTransformMakeScale(gesture.scale.x, gesture.scale.y); See here for a full fledged implementation of pinch-to-zoom.

Answer 3

Since iOS 7 you can set the zoom directly with the videoZoomFactor property of AVCaptureDevice.

Tie the scale property of the UIPinchGestureRecognizer to thevideoZoomFactor with a scaling constant. This will let you vary the sensitivity to taste:

-(void) handlePinchToZoomRecognizer:(UIPinchGestureRecognizer*)pinchRecognizer {
    const CGFloat pinchZoomScaleFactor = 2.0;

    if (pinchRecognizer.state == UIGestureRecognizerStateChanged) {
        NSError *error = nil;
        if ([videoDevice lockForConfiguration:&error]) {
            videoDevice.videoZoomFactor = 1.0 + pinchRecognizer.scale * pinchZoomScaleFactor;
            [videoDevice unlockForConfiguration];
        } else {
            NSLog(@"error: %@", error);
        }
    }
}

Note that AVCaptureDevice, along everything else related to AVCaptureSession, is not thread safe. So you probably don't want to do this from the main queue.

Answer 4

Swift 4
Add a pinch gesture recognizer to the front-most view and connect it to this action (pinchToZoom). captureDevice should be the instance currently providing input to the capture session. pinchToZoom provides smooth zooming for both front&back capture devices.

  @IBAction func pinchToZoom(_ pinch: UIPinchGestureRecognizer) {

    guard let device = captureDevice else { return }

    func minMaxZoom(_ factor: CGFloat) -> CGFloat { return min(max(factor, 1.0), device.activeFormat.videoMaxZoomFactor) }

    func update(scale factor: CGFloat) {
      do {
        try device.lockForConfiguration()
        defer { device.unlockForConfiguration() }
        device.videoZoomFactor = factor
      } catch {
        debugPrint(error)
      } 
    }

    let newScaleFactor = minMaxZoom(pinch.scale * zoomFactor)

    switch sender.state {
      case .began: fallthrough
      case .changed: update(scale: newScaleFactor)
      case .ended:
        zoomFactor = minMaxZoom(newScaleFactor)
        update(scale: zoomFactor)
     default: break
   }
 }

It'll be useful to declare zoomFactor on your camera or vc. I usually put it on the same singleton that has AVCaptureSession. This will act as a default value for captureDevice's videoZoomFactor.

var zoomFactor: Float = 1.0