Swift：同时自动对焦/曝光和连续自动对焦/曝光？

Question

现在，在我的相机应用程序中，我让用户触摸任意位置来设置焦点和曝光，但我怎样才能像 Apple 的相机应用程序一样获得两全其美的效果呢？

例如，用户可能希望通过触摸来关注前景中的某物，但如果场景变化足够大，它应该返回到连续自动对焦。同样，如果用户将相机对准灯光，它应该改变曝光以使其正确显示，然后当相机返回场景时，它应该再次修复曝光，使其不会太暗。但是，他们仍然可以选择将其调亮或调暗，具体取决于他们在相机视野中触摸的内容。

现在，当视图出现时，我将默认设置设置为屏幕中心：

func setDefaultFocusAndExposure() {

    let focusPoint = CGPoint(x:0.5,y:0.5)

    if let device = AVCaptureDevice.default(for:AVMediaType.video) {
        do {
            try device.lockForConfiguration()
            if device.isFocusPointOfInterestSupported {
                print(focusPoint)
                device.focusPointOfInterest = focusPoint
                device.focusMode = AVCaptureDevice.FocusMode.autoFocus
            }
            if device.isExposurePointOfInterestSupported {
                device.exposurePointOfInterest = focusPoint
                device.exposureMode = AVCaptureDevice.ExposureMode.autoExpose
            }
            device.unlockForConfiguration()

        } catch {
            // Handle errors here
            print("There was an error focusing the device's camera")
        }
    }

}

我还让用户根据他们触摸的位置设置焦点和曝光：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

    let bounds = UIScreen.main.bounds

    let touchPoint = touches.first! as UITouch
    let screenSize = bounds.size
    let focusPoint = CGPoint(x: touchPoint.location(in: view).y / screenSize.height, y: 1.0 - touchPoint.location(in: view).x / screenSize.width)

    if let device = AVCaptureDevice.default(for:AVMediaType.video) {
        do {
            try device.lockForConfiguration()
            if device.isFocusPointOfInterestSupported {
                device.focusPointOfInterest = focusPoint
                device.focusMode = AVCaptureDevice.FocusMode.autoFocus
            }
            if device.isExposurePointOfInterestSupported {
                device.exposurePointOfInterest = focusPoint
                device.exposureMode = AVCaptureDevice.ExposureMode.autoExpose
            }
            device.unlockForConfiguration()

        } catch {
            // Handle errors here
            print("There was an error focusing the device's camera")
        }
    }
}

Answer 1

想通了。首先我在 myViewDidAppear 上调用一个方法来设置我的默认焦点和曝光模式：

@objc func setDefaultFocusAndExposure() {

    if let device = AVCaptureDevice.default(for:AVMediaType.video) {
        do {
            try device.lockForConfiguration()
                device.isSubjectAreaChangeMonitoringEnabled = true
                device.focusMode = AVCaptureDevice.FocusMode.continuousAutoFocus
                device.exposureMode = AVCaptureDevice.ExposureMode.continuousAutoExposure
            device.unlockForConfiguration()

        } catch {
            // Handle errors here
            print("There was an error focusing the device's camera")
        }
    }
}

这里的诀窍是不要将自动对焦与连续自动对焦混淆。默认情况下，它会不断观察场景并设置焦点和曝光。另外 isSubjectAreaChangeMonitorEnabled 是一个非常重要的位。这使您可以注册通知以在场景更改焦点或曝光时调用函数，以便您可以切换焦点模式。稍后会详细介绍。

在触摸屏上可以根据一个点设置焦点和曝光：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

    let bounds = UIScreen.main.bounds

    let touchPoint = touches.first! as UITouch
    let screenSize = bounds.size
    let focusPoint = CGPoint(x: touchPoint.location(in: view).y / screenSize.height, y: 1.0 - touchPoint.location(in: view).x / screenSize.width)

    if let device = AVCaptureDevice.default(for:AVMediaType.video) {
        do {
            try device.lockForConfiguration()
            if device.isFocusPointOfInterestSupported {
                device.focusPointOfInterest = focusPoint
                device.focusMode = AVCaptureDevice.FocusMode.autoFocus
            }
            if device.isExposurePointOfInterestSupported {
                device.exposurePointOfInterest = focusPoint
                device.exposureMode = AVCaptureDevice.ExposureMode.autoExpose
            }
            device.unlockForConfiguration()

        } catch {
            // Handle errors here
            print("There was an error focusing the device's camera")
        }
    }
}

在 viewDidLoad 中注册通知以将焦点和曝光模式设置为连续。这里我只是调用了设置连续默认设置的函数：

    NotificationCenter.default.addObserver(self,
                                           selector: #selector(self.setDefaultFocusAndExposure),
                                           name: NSNotification.Name.AVCaptureDeviceSubjectAreaDidChange,
                                           object: nil)

不要忘记在 NotificationCenter 中移除观察者：

deinit {
    NotificationCenter.default.removeObserver(self)
}